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Title: A History of Science — Volume 3

Author: Henry Smith Williams
Edward Huntington Williams

Release date: April 1, 1999 [eBook #1707]
Most recently updated: January 29, 2013

Language: English

Other information and formats: www.gutenberg.org/ebooks/1707

Credits: Produced by Charles Keller, and David Widger

*** START OF THE PROJECT GUTENBERG EBOOK A HISTORY OF
SCIENCE — VOLUME 3 ***

A HISTORY OF SCIENCE

BY HENRY SMITH WILLIAMS, M.D., LL.D.

ASSISTED BY EDWARD H. WILLIAMS, M.D.

IN FIVE VOLUMES

VOLUME III.

CONTENTS

DETAILED CONTENTS

BOOK III. MODERN DEVELOPMENT OF THE
PHYSICAL SCIENCES

I. THE SUCCESSORS OF NEWTON IN ASTRONOMY
II. THE PROGRESS OF MODERN ASTRONOMY
III. THE NEW SCIENCE OF PALEONTOLOGY

IV. THE ORIGIN AND DEVELOPMENT OF MODERN
GEOLOGY
V. THE NEW SCIENCE OF METEOROLOGY
VI. MODERN THEORIES OF HEAT AND LIGHT
VII. THE MODERN DEVELOPMENT OF ELECTRICITY
AND MAGNETISM
VIII. THE CONSERVATION OF ENERGY
IX. THE ETHER AND PONDERABLE MATTER
APPENDIX

CONTENTS
BOOK III
CHAPTER I. THE SUCCESSORS OF NEWTON IN
ASTRONOMY
The work of Johannes Hevelius—Halley and Hevelius—
Halley's observation
of the transit of Mercury, and his method of determining the
parallax of
the planets—Halley's observation of meteors—His inability
to
explain these bodies—The important work of James Bradley
—Lacaille's
measurement of the arc of the meridian—The determination
of the
question as to the exact shape of the earth—D'Alembert and
his
influence upon science—Delambre's History of Astronomy—
The
astronomical work of Euler.
CHAPTER II. THE PROGRESS OF MODERN
ASTRONOMY
The work of William Herschel—His discovery of Uranus—
His discovery
that the stars are suns—His conception of the universe—His
deduction
that gravitation has caused the grouping of the heavenly
bodies—The
nebula, hypothesis,—Immanuel Kant's conception of the
formation of the
world—Defects in Kant's conception—Laplace's final
solution of the
problem—His explanation in detail—Change in the mental
attitude of the

world since Bruno—Asteroids and satellites—Discoveries of
Olbersl—The
mathematical calculations of Adams and Leverrier—The
discovery of the
inner ring of Saturn—Clerk Maxwell's paper on the stability
of Saturn's
rings—Helmholtz's conception of the action of tidal friction
—Professor
G. H. Darwin's estimate of the consequences of tidal action
—Comets
and meteors—Bredichin's cometary theory—The final
solution of the
structure of comets—Newcomb's estimate of the amount of
cometary dust
swept up daily by the earth—The fixed stars—John
Herschel's studies
of double stars—Fraunhofer's perfection of the refracting
telescope—Bessel's measurement of the parallax of a star,—
Henderson's
measurements—Kirchhoff and Bunsen's perfection of the
spectroscope—Wonderful revelations of the spectroscope—
Lord Kelvin's
estimate of the time that will be required for the earth to
become
completely cooled—Alvan Clark's discovery of the
companion star of
Sirius—The advent of the photographic film in astronomy—
Dr. Huggins's
studies of nebulae—Sir Norman Lockyer's "cosmogonic
guess,"—Croll's
pre-nebular theory.
CHAPTER III. THE NEW SCIENCE OF PALEONTOLOGY
William Smith and fossil shells—His discovery that fossil
rocks are
arranged in regular systems—Smith's inquiries taken up by
Cuvier—His
Ossements Fossiles containing the first description of hairy

elephant—His contention that fossils represent extinct
species
only—Dr. Buckland's studies of English fossil-beds—
Charles Lyell
combats catastrophism,—Elaboration of his ideas with
reference to
the rotation of species—The establishment of the doctrine of
uniformitarianism,—Darwin's Origin of Species—Fossil
man—Dr.
Falconer's visit to the fossil-beds in the valley of the
Somme—Investigations of Prestwich and Sir John Evans—
Discovery of the
Neanderthal skull,—Cuvier's rejection of human fossils—
The finding
of prehistoric carving on ivory—The fossil-beds of America
—Professor
Marsh's paper on the fossil horses in America—The Warren
mastodon,—The
Java fossil, Pithecanthropus Erectus.
CHAPTER IV. THE ORIGIN AND DEVELOPMENT OF
MODERN GEOLOGY
James Hutton and the study of the rocks—His theory of the
earth—His
belief in volcanic cataclysms in raising and forming the
continents—His
famous paper before the Royal Society of Edinburgh, 1781
—-His
conclusions that all strata of the earth have their origin at
the bottom
of the sea—-His deduction that heated and expanded matter
caused the
elevation of land above the sea-level—Indifference at first
shown this
remarkable paper—Neptunists versus Plutonists—Scrope's
classical work
on volcanoes—Final acceptance of Hutton's explanation of
the origin

of granites—Lyell and uniformitarianism—Observations on
the gradual
elevation of the coast-lines of Sweden and Patagonia—
Observations on
the enormous amount of land erosion constantly taking
place,—Agassiz
and the glacial theory—Perraudin the chamois-hunter, and
his
explanation of perched bowlders—De Charpentier's
acceptance of
Perraudin's explanation—Agassiz's paper on his Alpine
studies—His
conclusion that the Alps were once covered with an ice-sheet
—Final
acceptance of the glacial theory—The geological ages—The
work of
Murchison and Sedgwick—Formation of the American
continents—Past,
present, and future.
CHAPTER V. THE NEW SCIENCE OF METEOROLOGY
Biot's investigations of meteors—The observations of
Brandes and
Benzenberg on the velocity of falling stars—Professor
Olmstead's
observations on the meteoric shower of 1833—Confirmation
of Chladni's
hypothesis of 1794—The aurora borealis—Franklin's
suggestion that
it is of electrical origin—Its close association with
terrestrial
magnetism—Evaporation, cloud-formation, and dew—
Dalton's demonstration
that water exists in the air as an independent gas—Hutton's
theory of
rain—Luke Howard's paper on clouds—Observations on
dew, by Professor
Wilson and Mr. Six—Dr. Wells's essay on dew—His

observations
on several appearances connected with dew—Isotherms and
ocean
currents—Humboldt and the-science of comparative
climatology—His
studies of ocean currents—Maury's theory that gravity is the
cause
of ocean currents—Dr. Croll on Climate and Time—
Cyclones and
anti-cyclones,—Dove's studies in climatology—Professor
Ferrel's
mathematical law of the deflection of winds—Tyndall's
estimate of
the amount of heat given off by the liberation of a pound of
vapor—Meteorological observations and weather
predictions.
CHAPTER VI. MODERN THEORIES OF HEAT AND
LIGHT
Josiah Wedgwood and the clay pyrometer—Count Rumford
and the vibratory
theory of heat—His experiments with boring cannon to
determine the
nature of heat—Causing water to boil by the friction of the
borer—His
final determination that heat is a form of motion—Thomas
Young and the
wave theory of light—His paper on the theory of light and
colors—His
exposition of the colors of thin plates—Of the colors of thick
plates, and of striated surfaces,—Arago and Fresnel
champion the wave
theory—opposition to the theory by Biot—The French
Academy's tacit
acceptance of the correctness of the theory by its admission
of Fresnel
as a member.
CHAPTER VII. THE MODERN DEVELOPMENT OF

ELECTRICITY AND MAGNETISM
Galvani and the beginning of modern electricity—The
construction of
the voltaic pile—Nicholson's and Carlisle's discovery that
the galvanic
current decomposes water—Decomposition of various
substances by Sir
Humphry Davy—His construction of an arc-light—The
deflection of the
magnetic needle by electricity demonstrated by Oersted—
Effect of
this important discovery—Ampere creates the science of
electro-dynamics—Joseph Henry's studies of electromagnets
—Michael
Faraday begins his studies of electromagnetic induction—
His famous
paper before the Royal Society, in 1831, in which he
demonstrates
electro-magnetic induction—His explanation of Arago's
rotating disk—The search for a satisfactory method of
storing
electricity—Roentgen rays, or X-rays.
CHAPTER VIII. THE CONSERVATION OF ENERGY
Faraday narrowly misses the discovery of the doctrine of
conservation—Carnot's belief that a definite quantity of
work can be
transformed into a definite quantity of heat—The work of
James Prescott
Joule—Investigations begun by Dr. Mayer—Mayer's paper
of 1842—His
statement of the law of the conservation of energy—Mayer
and
Helmholtz—Joule's paper of 1843—Joule or Mayer—Lord
Kelvin and the
dissipation of energy-The final unification.
CHAPTER IX. THE ETHER AND PONDERABLE MATTER
James Clerk-Maxwell's conception of ether—Thomas Young

and
"Luminiferous ether,"—Young's and Fresnel's conception of
transverse
luminiferous undulations—Faraday's experiments pointing
to the
existence of ether—Professor Lodge's suggestion of two
ethers—Lord
Kelvin's calculation of the probable density of ether—The
vortex theory
of atoms—Helmholtz's calculations in vortex motions—
Professor
Tait's apparatus for creating vortex rings in the air—-The
ultimate
constitution of matter as conceived by Boscovich—Davy's
speculations
as to the changes that occur in the substance of matter at
different
temperatures—Clausius's and Maxwell's investigations of
the
kinetic theory of gases—Lord Kelvin's estimate of the size of
the
molecule—Studies of the potential energy of molecules—
Action of gases
at low temperatures.
APPENDIX

A HISTORY OF SCIENCE

BOOK III. MODERN DEVELOPMENT OF THE
PHYSICAL SCIENCES
With the present book we enter the field of the distinctively modern.
There is no precise date at which we take up each of the successive stories,
but the main sweep of development has to do in each case with the
nineteenth century. We shall see at once that this is a time both of rapid
progress and of great differentiation. We have heard almost nothing hitherto
of such sciences as paleontology, geology, and meteorology, each of which
now demands full attention. Meantime, astronomy and what the workers of
the elder day called natural philosophy become wonderfully diversified and
present numerous phases that would have been startling enough to the star-
gazers and philosophers of the earlier epoch.
Thus, for example, in the field of astronomy, Herschel is able, thanks to
his perfected telescope, to discover a new planet and then to reach out into
the depths of space and gain such knowledge of stars and nebulae as
hitherto no one had more than dreamed of. Then, in rapid sequence, a whole
coterie of hitherto unsuspected minor planets is discovered, stellar distances
are measured, some members of the starry galaxy are timed in their flight,
the direction of movement of the solar system itself is investigated, the
spectroscope reveals the chemical composition even of suns that are
unthinkably distant, and a tangible theory is grasped of the universal cycle
which includes the birth and death of worlds.
Similarly the new studies of the earth's surface reveal secrets of planetary
formation hitherto quite inscrutable. It becomes known that the strata of the
earth's surface have been forming throughout untold ages, and that
successive populations differing utterly from one another have peopled the
earth in different geological epochs. The entire point of view of thoughtful
men becomes changed in contemplating the history of the world in which
we live—albeit the newest thought harks back to some extent to those days
when the inspired thinkers of early Greece dreamed out the wonderful
theories with which our earlier chapters have made our readers familiar.

In the region of natural philosophy progress is no less pronounced and no
less striking. It suffices here, however, by way of anticipation, simply to
name the greatest generalization of the century in physical science—the
doctrine of the conservation of energy.

I. THE SUCCESSORS OF NEWTON IN
ASTRONOMY
HEVELIUS AND HALLEY
STRANGELY enough, the decade immediately following Newton was
one of comparative barrenness in scientific progress, the early years of the
eighteenth century not being as productive of great astronomers as the later
years of the seventeenth, or, for that matter, as the later years of the
eighteenth century itself. Several of the prominent astronomers of the later
seventeenth century lived on into the opening years of the following
century, however, and the younger generation soon developed a coterie of
astronomers, among whom Euler, Lagrange, Laplace, and Herschel, as we
shall see, were to accomplish great things in this field before the century
closed.
One of the great seventeenth-century astronomers, who died just before
the close of the century, was Johannes Hevelius (1611-1687), of Dantzig,
who advanced astronomy by his accurate description of the face and the
spots of the moon. But he is remembered also for having retarded progress
by his influence in refusing to use telescopic sights in his observations,
preferring until his death the plain sights long before discarded by most
other astronomers. The advantages of these telescope sights have been
discussed under the article treating of Robert Hooke, but no such
advantages were ever recognized by Hevelius. So great was Hevelius's
reputation as an astronomer that his refusal to recognize the advantage of
the telescope sights caused many astronomers to hesitate before accepting
them as superior to the plain; and even the famous Halley, of whom we
shall speak further in a moment, was sufficiently in doubt over the matter to
pay the aged astronomer a visit to test his skill in using the old-style sights.
Side by side, Hevelius and Halley made their observations, Hevelius with
his old instrument and Halley with the new. The results showed slightly in
the younger man's favor, but not enough to make it an entirely convincing
demonstration. The explanation of this, however, did not lie in the lack of
superiority of the telescopic instrument, but rather in the marvellous skill of

the aged Hevelius, whose dexterity almost compensated for the defect of his
instrument. What he might have accomplished could he have been induced
to adopt the telescope can only be surmised.
Halley himself was by no means a tyro in matters astronomical at that
time. As the only son of a wealthy soap-boiler living near London, he had
been given a liberal education, and even before leaving college made such
novel scientific observations as that of the change in the variation of the
compass. At nineteen years of age he discovered a new method of
determining the elements of the planetary orbits which was a distinct
improvement over the old. The year following he sailed for the Island of St,
Helena to make observations of the heavens in the southern hemisphere.
It was while in St. Helena that Halley made his famous observation of the
transit of Mercury over the sun's disk, this observation being connected,
indirectly at least, with his discovery of a method of determining the
parallax of the planets. By parallax is meant the apparent change in the
position of an object, due really to a change in the position of the observer.
Thus, if we imagine two astronomers making observations of the sun from
opposite sides of the earth at the same time, it is obvious that to these
observers the sun will appear to be at two different points in the sky. Half
the angle measuring this difference would be known as the sun's parallax.
This would depend, then, upon the distance of the earth from the sun and
the length of the earth's radius. Since the actual length of this radius has
been determined, the parallax of any heavenly body enables the astronomer
to determine its exact distance.
The parallaxes can be determined equally well, however, if two observers
are separated by exactly known distances, several hundreds or thousands of
miles apart. In the case of a transit of Venus across the sun's disk, for
example, an observer at New York notes the image of the planet moving
across the sun's disk, and notes also the exact time of this observation. In
the same manner an observer at London makes similar observations.
Knowing the distance between New York and London, and the different
time of the passage, it is thus possible to calculate the difference of the
parallaxes of the sun and a planet crossing its disk. The idea of thus
determining the parallax of the planets originated, or at least was developed,
by Halley, and from this phenomenon he thought it possible to conclude the

dimensions of all the planetary orbits. As we shall see further on, his views
were found to be correct by later astronomers.
In 1721 Halley succeeded Flamsteed as astronomer royal at the
Greenwich Observatory. Although sixty-four years of age at that time his
activity in astronomy continued unabated for another score of years. At
Greenwich he undertook some tedious observations of the moon, and
during those observations was first to detect the acceleration of mean
motion. He was unable to explain this, however, and it remained for
Laplace in the closing years of the century to do so, as we shall see later.
Halley's book, the Synopsis Astronomiae Cometicae, is one of the most
valuable additions to astronomical literature since the time of Kepler. He
was first to attempt the calculation of the orbit of a comet, having revived
the ancient opinion that comets belong to the solar system, moving in
eccentric orbits round the sun, and his calculation of the orbit of the comet
of 1682 led him to predict correctly the return of that comet in 1758.
Halley's Study of Meteors.
Like other astronomers of his time he was greatly puzzled over the well-
known phenomena of shooting-stars, or meteors, making many
observations himself, and examining carefully the observations of other
astronomers. In 1714 he gave his views as to the origin and composition of
these mysterious visitors in the earth's atmosphere. As this subject will be
again referred to in a later chapter, Halley's views, representing the most
advanced views of his age, are of interest.
"The theory of the air seemeth at present," he says, "to be perfectly well
understood, and the differing densities thereof at all altitudes; for supposing
the same air to occupy spaces reciprocally proportional to the quantity of
the superior or incumbent air, I have elsewhere proved that at forty miles
high the air is rarer than at the surface of the earth at three thousand times;
and that the utmost height of the atmosphere, which reflects light in the
Crepusculum, is not fully forty-five miles, notwithstanding which 'tis still
manifest that some sort of vapors, and those in no small quantity, arise
nearly to that height. An instance of this may be given in the great light the
society had an account of (vide Transact. Sep., 1676) from Dr. Wallis,
which was seen in very distant counties almost over all the south part of
England. Of which though the doctor could not get so particular a relation

as was requisite to determine the height thereof, yet from the distant places
it was seen in, it could not but be very many miles high.
"So likewise that meteor which was seen in 1708, on the 31st of July,
between nine and ten o'clock at night, was evidently between forty and fifty
miles perpendicularly high, and as near as I can gather, over Shereness and
the buoy on the Nore. For it was seen at London moving horizontally from
east by north to east by south at least fifty degrees high, and at Redgrove, in
Suffolk, on the Yarmouth road, about twenty miles from the east coast of
England, and at least forty miles to the eastward of London, it appeared a
little to the westward of the south, suppose south by west, and was seen
about thirty degrees high, sliding obliquely downward. I was shown in both
places the situation thereof, which was as described, but could wish some
person skilled in astronomical matters bad seen it, that we might pronounce
concerning its height with more certainty. Yet, as it is, we may securely
conclude that it was not many more miles westerly than Redgrove, which,
as I said before, is about forty miles more easterly than London. Suppose it,
therefore, where perpendicular, to have been thirty-five miles east from
London, and by the altitude it appeared at in London—viz., fifty degrees, its
tangent will be forty-two miles, for the height of the meteor above the
surface of the earth; which also is rather of the least, because the altitude of
the place shown me is rather more than less than fifty degrees; and the like
may be concluded from the altitude it appeared in at Redgrove, near seventy
miles distant. Though at this very great distance, it appeared to move with
an incredible velocity, darting, in a very few seconds of time, for about
twelve degrees of a great circle from north to south, being very bright at its
first appearance; and it died away at the east of its course, leaving for some
time a pale whiteness in the place, with some remains of it in the track
where it had gone; but no hissing sound as it passed, or bounce of an
explosion were heard.
"It may deserve the honorable society's thoughts, how so great a quantity
of vapor should be raised to the top of the atmosphere, and there collected,
so as upon its ascension or otherwise illumination, to give a light to a circle
of above one hundred miles diameter, not much inferior to the light of the
moon; so as one might see to take a pin from the ground in the otherwise
dark night. 'Tis hard to conceive what sort of exhalations should rise from
the earth, either by the action of the sun or subterranean heat, so as to

surmount the extreme cold and rareness of the air in those upper regions:
but the fact is indisputable, and therefore requires a solution."
From this much of the paper it appears that there was a general belief that
this burning mass was heated vapor thrown off from the earth in some
mysterious manner, yet this is unsatisfactory to Halley, for after citing
various other meteors that have appeared within his knowledge, he goes on
to say:
"What sort of substance it must be, that could be so impelled and ignited
at the same time; there being no Vulcano or other Spiraculum of
subterraneous fire in the northeast parts of the world, that we ever yet heard
of, from whence it might be projected.
"I have much considered this appearance, and think it one of the hardest
things to account for that I have yet met with in the phenomena of meteors,
and I am induced to think that it must be some collection of matter formed
in the aether, as it were, by some fortuitous concourse of atoms, and that the
earth met with it as it passed along in its orb, then but newly formed, and
before it had conceived any great impetus of descent towards the sun. For
the direction of it was exactly opposite to that of the earth, which made an
angle with the meridian at that time of sixty-seven gr., that is, its course was
from west southwest to east northeast, wherefore the meteor seemed to
move the contrary way. And besides falling into the power of the earth's
gravity, and losing its motion from the opposition of the medium, it seems
that it descended towards the earth, and was extinguished in the Tyrrhene
Sea, to the west southwest of Leghorn. The great blow being heard upon its
first immersion into the water, and the rattling like the driving of a cart over
stones being what succeeded upon its quenching; something like this is
always heard upon quenching a very hot iron in water. These facts being
past dispute, I would be glad to have the opinion of the learned thereon, and
what objection can be reasonably made against the above hypothesis, which
I humbly submit to their censure."(1)
These few paragraphs, coming as they do from a leading eighteenth-
century astronomer, convey more clearly than any comment the actual state
of the meteorological learning at that time. That this ball of fire, rushing "at
a greater velocity than the swiftest cannon-ball," was simply a mass of
heated rock passing through our atmosphere, did not occur to him, or at
least was not credited. Nor is this surprising when we reflect that at that

time universal gravitation had been but recently discovered; heat had not as
yet been recognized as simply a form of motion; and thunder and lightning
were unexplained mysteries, not to be explained for another three-quarters
of a century. In the chapter on meteorology we shall see how the solution of
this mystery that puzzled Halley and his associates all their lives was finally
attained.
BRADLEY AND THE ABERRATION OF LIGHT
Halley was succeeded as astronomer royal by a man whose useful
additions to the science were not to be recognized or appreciated fully until
brought to light by the Prussian astronomer Bessel early in the nineteenth
century. This was Dr. James Bradley, an ecclesiastic, who ranks as one of
the most eminent astronomers of the eighteenth century. His most
remarkable discovery was the explanation of a peculiar motion of the pole-
star, first observed, but not explained, by Picard a century before. For many
years a satisfactory explanation was sought unsuccessfully by Bradley and
his fellow-astronomers, but at last he was able to demonstrate that the stary
Draconis, on which he was making his observations, described, or appeared
to describe, a small ellipse. If this observation was correct, it afforded a
means of computing the aberration of any star at all times. The explanation
of the physical cause of this aberration, as Bradley thought, and afterwards
demonstrated, was the result of the combination of the motion of light with
the annual motion of the earth. Bradley first formulated this theory in 1728,
but it was not until 1748—twenty years of continuous struggle and
observation by him—that he was prepared to communicate the results of his
efforts to the Royal Society. This remarkable paper is thought by the
Frenchman, Delambre, to entitle its author to a place in science beside such
astronomers as Hipparcbus and Kepler.
Bradley's studies led him to discover also the libratory motion of the
earth's axis. "As this appearance of Draconis indicated a diminution of the
inclination of the earth's axis to the plane of the ecliptic," he says; "and as
several astronomers have supposed THAT inclination to diminish regularly;
if this phenomenon depended upon such a cause, and amounted to 18" in
nine years, the obliquity of the ecliptic would, at that rate, alter a whole
minute in thirty years; which is much faster than any observations, before
made, would allow. I had reason, therefore, to think that some part of this
motion at the least, if not the whole, was owing to the moon's action upon

the equatorial parts of the earth; which, I conceived, might cause a libratory
motion of the earth's axis. But as I was unable to judge, from only nine
years observations, whether the axis would entirely recover the same
position that it had in the year 1727, I found it necessary to continue my
observations through a whole period of the moon's nodes; at the end of
which I had the satisfaction to see, that the stars, returned into the same
position again; as if there had been no alteration at all in the inclination of
the earth's axis; which fully convinced me that I had guessed rightly as to
the cause of the phenomena. This circumstance proves likewise, that if there
be a gradual diminution of the obliquity of the ecliptic, it does not arise only
from an alteration in the position of the earth's axis, but rather from some
change in the plane of the ecliptic itself; because the stars, at the end of the
period of the moon's nodes, appeared in the same places, with respect to the
equator, as they ought to have done, if the earth's axis had retained the same
inclination to an invariable plane."(2)
FRENCH ASTRONOMERS
Meanwhile, astronomers across the channel were by no means idle. In
France several successful observers were making many additions to the
already long list of observations of the first astronomer of the Royal
Observatory of Paris, Dominic Cassini (1625-1712), whose reputation
among his contemporaries was much greater than among succeeding
generations of astronomers. Perhaps the most deserving of these successors
was Nicolas Louis de Lacaille (1713-1762), a theologian who had been
educated at the expense of the Duke of Bourbon, and who, soon after
completing his clerical studies, came under the patronage of Cassini, whose
attention had been called to the young man's interest in the sciences. One of
Lacaille's first under-takings was the remeasuring of the French are of the
meridian, which had been incorrectly measured by his patron in 1684. This
was begun in 1739, and occupied him for two years before successfully
completed. As a reward, however, he was admitted to the academy and
appointed mathematical professor in Mazarin College.
In 1751 he went to the Cape of Good Hope for the purpose of
determining the sun's parallax by observations of the parallaxes of Mars and
Venus, and incidentally to make observations on the other southern
hemisphere stars. The results of this undertaking were most successful, and
were given in his Coelum australe stelligerum, etc., published in 1763. In

this he shows that in the course of a single year he had observed some ten
thousand stars, and computed the places of one thousand nine hundred and
forty-two of them, measured a degree of the meridian, and made many
observations of the moon—productive industry seldom equalled in a single
year in any field. These observations were of great service to the
astronomers, as they afforded the opportunity of comparing the stars of the
southern hemisphere with those of the northern, which were being observed
simultaneously by Lelande at Berlin.
Lacaille's observations followed closely upon the determination of an
absorbing question which occupied the attention of the astronomers in the
early part of the century. This question was as to the shape of the earth—
whether it was actually flattened at the poles. To settle this question once
for all the Academy of Sciences decided to make the actual measurement of
the length of two degrees, one as near the pole as possible, the other at the
equator. Accordingly, three astronomers, Godin, Bouguer, and La
Condamine, made the journey to a spot on the equator in Peru, while four
astronomers, Camus, Clairaut, Maupertuis, and Lemonnier, made a voyage
to a place selected in Lapland. The result of these expeditions was the
determination that the globe is oblately spheroidal.
A great contemporary and fellow-countryman of Lacaille was Jean Le
Rond d'Alembert (1717-1783), who, although not primarily an astronomer,
did so much with his mathematical calculations to aid that science that his
name is closely connected with its progress during the eighteenth century.
D'Alembert, who became one of the best-known men of science of his day,
and whose services were eagerly sought by the rulers of Europe, began life
as a foundling, having been exposed in one of the markets of Paris. The
sickly infant was adopted and cared for in the family of a poor glazier, and
treated as a member of the family. In later years, however, after the
foundling had become famous throughout Europe, his mother, Madame
Tencin, sent for him, and acknowledged her relationship. It is more than
likely that the great philosopher believed her story, but if so he did not
allow her the satisfaction of knowing his belief, declaring always that
Madame Tencin could "not be nearer than a step-mother to him, since his
mother was the wife of the glazier."
D'Alembert did much for the cause of science by his example as well as
by his discoveries. By living a plain but honest life, declining magnificent

offers of positions from royal patrons, at the same time refusing to grovel
before nobility, he set a worthy example to other philosophers whose
cringing and pusillanimous attitude towards persons of wealth or position
had hitherto earned them the contempt of the upper classes.
His direct additions to astronomy are several, among others the
determination of the mutation of the axis of the earth. He also determined
the ratio of the attractive forces of the sun and moon, which he found to be
about as seven to three. From this he reached the conclusion that the earth
must be seventy times greater than the moon. The first two volumes of his
Researches on the Systems of the World, published in 1754, are largely
devoted to mathematical and astronomical problems, many of them of little
importance now, but of great interest to astronomers at that time.
Another great contemporary of D'Alembert, whose name is closely
associated and frequently confounded with his, was Jean Baptiste Joseph
Delambre (1749-1822). More fortunate in birth as also in his educational
advantages, Delambre as a youth began his studies under the celebrated
poet Delille. Later he was obliged to struggle against poverty, supporting
himself for a time by making translations from Latin, Greek, Italian, and
English, and acting as tutor in private families. The turning-point of his
fortune came when the attention of Lalande was called to the young man by
his remarkable memory, and Lalande soon showed his admiration by giving
Delambre certain difficult astronomical problems to solve. By performing
these tasks successfully his future as an astronomer became assured. At that
time the planet Uranus had just been discovered by Herschel, and the
Academy of Sciences offered as the subject for one of its prizes the
determination of the planet's orbit. Delambre made this determination and
won the prize—a feat that brought him at once into prominence.
By his writings he probably did as much towards perfecting modern
astronomy as any one man. His History of Astronomy is not merely a
narrative of progress of astronomy but a complete abstract of all the
celebrated works written on the subject. Thus he became famous as an
historian as well as an astronomer.
LEONARD EULER
Still another contemporary of D'Alembert and Delambre, and somewhat
older than either of them, was Leonard Euler (1707-1783), of Basel, whose
fame as a philosopher equals that of either of the great Frenchmen. He is of

particular interest here in his capacity of astronomer, but astronomy was
only one of the many fields of science in which he shone. Surely something
out of the ordinary was to be expected of the man who could "repeat the
AEneid of Virgil from the beginning to the end without hesitation, and
indicate the first and last line of every page of the edition which he used."
Something was expected, and he fulfilled these expectations.
In early life he devoted himself to the study of theology and the Oriental
languages, at the request of his father, but his love of mathematics proved
too strong, and, with his father's consent, he finally gave up his classical
studies and turned to his favorite study, geometry. In 1727 he was invited by
Catharine I. to reside in St. Petersburg, and on accepting this invitation he
was made an associate of the Academy of Sciences. A little later he was
made professor of physics, and in 1733 professor of mathematics. In 1735
he solved a problem in three days which some of the eminent
mathematicians would not undertake under several months. In 1741
Frederick the Great invited him to Berlin, where he soon became a member
of the Academy of Sciences and professor of mathematics; but in 1766 he
returned to St. Petersburg. Towards the close of his life he became virtually
blind, being obliged to dictate his thoughts, sometimes to persons entirely
ignorant of the subject in hand. Nevertheless, his remarkable memory, still
further heightened by his blindness, enabled him to carry out the elaborate
computations frequently involved.
Euler's first memoir, transmitted to the Academy of Sciences of Paris in
1747, was on the planetary perturbations. This memoir carried off the prize
that had been offered for the analytical theory of the motions of Jupiter and
Saturn. Other memoirs followed, one in 1749 and another in 1750, with
further expansions of the same subject. As some slight errors were found in
these, such as a mistake in some of the formulae expressing the secular and
periodic inequalities, the academy proposed the same subject for the prize
of 1752. Euler again competed, and won this prize also. The contents of this
memoir laid the foundation for the subsequent demonstration of the
permanent stability of the planetary system by Laplace and Lagrange.
It was Euler also who demonstrated that within certain fixed limits the
eccentricities and places of the aphelia of Saturn and Jupiter are subject to
constant variation, and he calculated that after a lapse of about thirty

thousand years the elements of the orbits of these two planets recover their
original values.

II. THE PROGRESS OF MODERN
ASTRONOMY
A NEW epoch in astronomy begins with the work of William Herschel,
the Hanoverian, whom England made hers by adoption. He was a man with
a positive genius for sidereal discovery. At first a mere amateur in
astronomy, he snatched time from his duties as music-teacher to grind him a
telescopic mirror, and began gazing at the stars. Not content with his first
telescope, he made another and another, and he had such genius for the
work that he soon possessed a better instrument than was ever made before.
His patience in grinding the curved reflective surface was monumental.
Sometimes for sixteen hours together he must walk steadily about the
mirror, polishing it, without once removing his hands. Meantime his sister,
always his chief lieutenant, cheered him with her presence, and from time
to time put food into his mouth. The telescope completed, the astronomer
turned night into day, and from sunset to sunrise, year in and year out,
swept the heavens unceasingly, unless prevented by clouds or the brightness
of the moon. His sister sat always at his side, recording his observations.
They were in the open air, perched high at the mouth of the reflector, and
sometimes it was so cold that the ink froze in the bottle in Caroline
Herschel's hand; but the two enthusiasts hardly noticed a thing so common-
place as terrestrial weather. They were living in distant worlds.
The results? What could they be? Such enthusiasm would move
mountains. But, after all, the moving of mountains seems a liliputian task
compared with what Herschel really did with those wonderful telescopes.
He moved worlds, stars, a universe—even, if you please, a galaxy of
universes; at least he proved that they move, which seems scarcely less
wonderful; and he expanded the cosmos, as man conceives it, to thousands
of times the dimensions it had before. As a mere beginning, he doubled the
diameter of the solar system by observing the great outlying planet which
we now call Uranus, but which he christened Georgium Sidus, in honor of
his sovereign, and which his French contemporaries, not relishing that
name, preferred to call Herschel.

This discovery was but a trifle compared with what Herschel did later on,
but it gave him world-wide reputation none the less. Comets and moons
aside, this was the first addition to the solar system that had been made
within historic times, and it created a veritable furor of popular interest and
enthusiasm. Incidentally King George was flattered at having a world
named after him, and he smiled on the astronomer, and came with his court
to have a look at his namesake. The inspection was highly satisfactory; and
presently the royal favor enabled the astronomer to escape the thraldom of
teaching music and to devote his entire time to the more congenial task of
star-gazing.
Thus relieved from the burden of mundane embarrassments, he turned
with fresh enthusiasm to the skies, and his discoveries followed one another
in bewildering profusion. He found various hitherto unseen moons of our
sister planets; he made special studies of Saturn, and proved that this planet,
with its rings, revolves on its axis; he scanned the spots on the sun, and
suggested that they influence the weather of our earth; in short, he extended
the entire field of solar astronomy. But very soon this field became too
small for him, and his most important researches carried him out into the
regions of space compared with which the span of our solar system is a
mere point. With his perfected telescopes he entered abysmal vistas which
no human eve ever penetrated before, which no human mind had hitherto
more than vaguely imagined. He tells us that his forty-foot reflector will
bring him light from a distance of "at least eleven and three-fourths millions
of millions of millions of miles"—light which left its source two million
years ago. The smallest stars visible to the unaided eye are those of the sixth
magnitude; this telescope, he thinks, has power to reveal stars of the 1342d
magnitude.
But what did Herschel learn regarding these awful depths of space and
the stars that people them? That was what the world wished to know.
Copernicus, Galileo, Kepler, had given us a solar system, but the stars had
been a mystery. What says the great reflector—are the stars points of light,
as the ancients taught, and as more than one philosopher of the eighteenth
century has still contended, or are they suns, as others hold? Herschel
answers, they are suns, each and every one of all the millions—suns, many
of them, larger than the one that is the centre of our tiny system. Not only
so, but they are moving suns. Instead of being fixed in space, as has been
thought, they are whirling in gigantic orbits about some common centre. Is

our sun that centre? Far from it. Our sun is only a star like all the rest,
circling on with its attendant satellites—our giant sun a star, no different
from myriad other stars, not even so large as some; a mere insignificant
spark of matter in an infinite shower of sparks.
Nor is this all. Looking beyond the few thousand stars that are visible to
the naked eye, Herschel sees series after series of more distant stars,
marshalled in galaxies of millions; but at last he reaches a distance beyond
which the galaxies no longer increase. And yet—so he thinks—he has not
reached the limits of his vision. What then? He has come to the bounds of
the sidereal system—seen to the confines of the universe. He believes that
he can outline this system, this universe, and prove that it has the shape of
an irregular globe, oblately flattened to almost disklike proportions, and
divided at one edge—a bifurcation that is revealed even to the naked eye in
the forking of the Milky Way.
This, then, is our universe as Herschel conceives it—a vast galaxy of
suns, held to one centre, revolving, poised in space. But even here those
marvellous telescopes do not pause. Far, far out beyond the confines of our
universe, so far that the awful span of our own system might serve as a unit
of measure, are revealed other systems, other universes, like our own, each
composed, as he thinks, of myriads of suns, clustered like our galaxy into
an isolated system—mere islands of matter in an infinite ocean of space. So
distant from our universe are these now universes of Herschel's discovery
that their light reaches us only as a dim, nebulous glow, in most cases
invisible to the unaided eye. About a hundred of these nebulae were known
when Herschel began his studies. Before the close of the century he had
discovered about two thousand more of them, and many of these had been
resolved by his largest telescopes into clusters of stars. He believed that the
farthest of these nebulae that he could see was at least three hundred
thousand times as distant from us as the nearest fixed star. Yet that nearest
star—so more recent studies prove—is so remote that its light, travelling
one hundred and eighty thousand miles a second, requires three and one-
half years to reach our planet.
As if to give the finishing touches to this novel scheme of cosmology,
Herschel, though in the main very little given to unsustained theorizing,
allows himself the privilege of one belief that he cannot call upon his
telescope to substantiate. He thinks that all the myriad suns of his

numberless systems are instinct with life in the human sense. Giordano
Bruno and a long line of his followers had held that some of our sister
planets may be inhabited, but Herschel extends the thought to include the
moon, the sun, the stars—all the heavenly bodies. He believes that he can
demonstrate the habitability of our own sun, and, reasoning from analogy,
he is firmly convinced that all the suns of all the systems are "well supplied
with inhabitants." In this, as in some other inferences, Herschel is misled by
the faulty physics of his time. Future generations, working with perfected
instruments, may not sustain him all along the line of his observations,
even, let alone his inferences. But how one's egotism shrivels and shrinks as
one grasps the import of his sweeping thoughts!
Continuing his observations of the innumerable nebulae, Herschel is led
presently to another curious speculative inference. He notes that some star
groups are much more thickly clustered than others, and he is led to infer
that such varied clustering tells of varying ages of the different nebulae. He
thinks that at first all space may have been evenly sprinkled with the stars
and that the grouping has resulted from the action of gravitation.
"That the Milky Way is a most extensive stratum of stars of various sizes
admits no longer of lasting doubt," he declares, "and that our sun is actually
one of the heavenly bodies belonging to it is as evident. I have now viewed
and gauged this shining zone in almost every direction and find it composed
of stars whose number... constantly increases and decreases in proportion to
its apparent brightness to the naked eye.
"Let us suppose numberless stars of various sizes, scattered over an
indefinite portion of space in such a manner as to be almost equally
distributed throughout the whole. The laws of attraction which no doubt
extend to the remotest regions of the fixed stars will operate in such a
manner as most probably to produce the following effects:
"In the first case, since we have supposed the stars to be of various sizes,
it will happen that a star, being considerably larger than its neighboring
ones, will attract them more than they will be attracted by others that are
immediately around them; by which means they will be, in time, as it were,
condensed about a centre, or, in other words, form themselves into a cluster
of stars of almost a globular figure, more or less regular according to the
size and distance of the surrounding stars....

"The next case, which will also happen almost as frequently as the
former, is where a few stars, though not superior in size to the rest, may
chance to be rather nearer one another than the surrounding ones,... and this
construction admits of the utmost variety of shapes....
"From the composition and repeated conjunction of both the foregoing
formations, a third may be derived when many large stars, or combined
small ones, are spread in long, extended, regular, or crooked rows, streaks,
or branches; for they will also draw the surrounding stars, so as to produce
figures of condensed stars curiously similar to the former which gave rise to
these condensations.
"We may likewise admit still more extensive combinations; when, at the
same time that a cluster of stars is forming at the one part of space, there
may be another collection in a different but perhaps not far-distant quarter,
which may occasion a mutual approach towards their own centre of gravity.
"In the last place, as a natural conclusion of the former cases, there will
be formed great cavities or vacancies by the retreating of the stars towards
the various centres which attract them."(1)
Looking forward, it appears that the time must come when all the suns of
a system will be drawn together and destroyed by impact at a common
centre. Already, it seems to Herschel, the thickest clusters have "outlived
their usefulness" and are verging towards their doom.
But again, other nebulae present an appearance suggestive of an opposite
condition. They are not resolvable into stars, but present an almost uniform
appearance throughout, and are hence believed to be composed of a shining
fluid, which in some instances is seen to be condensed at the centre into a
glowing mass. In such a nebula Herschel thinks he sees a sun in process of
formation.
THE NEBULAR HYPOTHESIS OF KANT
Taken together, these two conceptions outline a majestic cycle of world
formation and world destruction—a broad scheme of cosmogony, such as
had been vaguely adumbrated two centuries before by Kepler and in more
recent times by Wright and Swedenborg. This so-called "nebular
hypothesis" assumes that in the beginning all space was uniformly filled
with cosmic matter in a state of nebular or "fire-mist" diffusion, "formless
and void." It pictures the condensation—coagulation, if you will—of

portions of this mass to form segregated masses, and the ultimate
development out of these masses of the sidereal bodies that we see.
Perhaps the first elaborate exposition of this idea was that given by the
great German philosopher Immanuel Kant (born at Konigsberg in 1724,
died in 1804), known to every one as the author of the Critique of Pure
Reason. Let us learn from his own words how the imaginative philosopher
conceived the world to have come into existence.
"I assume," says Kant, "that all the material of which the globes
belonging to our solar system—all the planets and comets—consist, at the
beginning of all things was decomposed into its primary elements, and
filled the whole space of the universe in which the bodies formed out of it
now revolve. This state of nature, when viewed in and by itself without any
reference to a system, seems to be the very simplest that can follow upon
nothing. At that time nothing has yet been formed. The construction of
heavenly bodies at a distance from one another, their distances regulated by
their attraction, their form arising out of the equilibrium of their collected
matter, exhibit a later state.... In a region of space filled in this manner, a
universal repose could last only a moment. The elements have essential
forces with which to put each other in motion, and thus are themselves a
source of life. Matter immediately begins to strive to fashion itself. The
scattered elements of a denser kind, by means of their attraction, gather
from a sphere around them all the matter of less specific gravity; again,
these elements themselves, together with the material which they have
united with them, collect in those points where the particles of a still denser
kind are found; these in like manner join still denser particles, and so on. If
we follow in imagination this process by which nature fashions itself into
form through the whole extent of chaos, we easily perceive that all the
results of the process would consist in the formation of divers masses
which, when their formation was complete, would by the equality of their
attraction be at rest and be forever unmoved.
"But nature has other forces in store which are specially exerted when
matter is decomposed into fine particles. They are those forces by which
these particles repel one another, and which, by their conflict with
attractions, bring forth that movement which is, as it were, the lasting life of
nature. This force of repulsion is manifested in the elasticity of vapors, the
effluences of strong-smelling bodies, and the diffusion of all spirituous

matters. This force is an uncontestable phenomenon of matter. It is by it that
the elements, which may be falling to the point attracting them, are turned
sideways promiscuously from their movement in a straight line; and their
perpendicular fall thereby issues in circular movements, which encompass
the centre towards which they were falling. In order to make the formation
of the world more distinctly conceivable, we will limit our view by
withdrawing it from the infinite universe of nature and directing it to a
particular system, as the one which belongs to our sun. Having considered
the generation of this system, we shall be able to advance to a similar
consideration of the origin of the great world-systems, and thus to embrace
the infinitude of the whole creation in one conception.
"From what has been said, it will appear that if a point is situated in a
very large space where the attraction of the elements there situated acts
more strongly than elsewhere, then the matter of the elementary particles
scattered throughout the whole region will fall to that point. The first effect
of this general fall is the formation of a body at this centre of attraction,
which, so to speak, grows from an infinitely small nucleus by rapid strides;
and in the proportion in which this mass increases, it also draws with
greater force the surrounding particles to unite with it. When the mass of
this central body has grown so great that the velocity with which it draws
the particles to itself with great distances is bent sideways by the feeble
degree of repulsion with which they impede one another, and when it issues
in lateral movements which are capable by means of the centrifugal force of
encompassing the central body in an orbit, then there are produced whirls or
vortices of particles, each of which by itself describes a curved line by the
composition of the attracting force and the force of revolution that had been
bent sideways. These kinds of orbits all intersect one another, for which
their great dispersion in this space gives place. Yet these movements are in
many ways in conflict with one another, and they naturally tend to bring
one another to a uniformity—that is, into a state in which one movement is
as little obstructive to the other as possible. This happens in two ways: first
by the particles limiting one another's movement till they all advance in one
direction; and, secondly, in this way, that the particles limit their vertical
movements in virtue of which they are approaching the centre of attraction,
till they all move horizontally—i. e., in parallel circles round the sun as
their centre, no longer intercept one another, and by the centrifugal force
becoming equal with the falling force they keep themselves constantly in

free circular orbits at the distance at which they move. The result, finally, is
that only those particles continue to move in this region of space which
have acquired by their fall a velocity, and through the resistance of the other
particles a direction, by which they can continue to maintain a FREE
CIRCULAR MOVEMENT....
"The view of the formation of the planets in this system has the
advantage over every other possible theory in holding that the origin of the
movements, and the position of the orbits in arising at that same point of
time—nay, more, in showing that even the deviations from the greatest
possible exactness in their determinations, as well as the accordances
themselves, become clear at a glance. The planets are formed out of
particles which, at the distance at which they move, have exact movements
in circular orbits; and therefore the masses composed out of them will
continue the same movements and at the same rate and in the same
direction."(2)
It must be admitted that this explanation leaves a good deal to be desired.
It is the explanation of a metaphysician rather than that of an experimental
scientist. Such phrases as "matter immediately begins to strive to fashion
itself," for example, have no place in the reasoning of inductive science.
Nevertheless, the hypothesis of Kant is a remarkable conception; it attempts
to explain along rational lines something which hitherto had for the most
part been considered altogether inexplicable.
But there are various questions that at once suggest themselves which the
Kantian theory leaves unanswered. How happens it, for example, that the
cosmic mass which gave birth to our solar system was divided into several
planetary bodies instead of remaining a single mass? Were the planets
struck from the sun by the chance impact of comets, as Buffon has
suggested? or thrown out by explosive volcanic action, in accordance with
the theory of Dr. Darwin? or do they owe their origin to some unknown
law? In any event, how chanced it that all were projected in nearly the same
plane as we now find them?
LAPLACE AND THE NEBULAR HYPOTHESIS
It remained for a mathematical astronomer to solve these puzzles. The
man of all others competent to take the subject in hand was the French
astronomer Laplace. For a quarter of a century he had devoted his
transcendent mathematical abilities to the solution of problems of motion of

the heavenly bodies. Working in friendly rivalry with his countryman
Lagrange, his only peer among the mathematicians of the age, he had taken
up and solved one by one the problems that Newton left obscure. Largely
through the efforts of these two men the last lingering doubts as to the
solidarity of the Newtonian hypothesis of universal gravitation had been
removed. The share of Lagrange was hardly less than that of his co-worker;
but Laplace will longer be remembered, because he ultimately brought his
completed labors into a system, and, incorporating with them the labors of
his contemporaries, produced in the Mecanique Celeste the undisputed
mathematical monument of the century, a fitting complement to the
Principia of Newton, which it supplements and in a sense completes.
In the closing years of the eighteenth century Laplace took up the nebular
hypothesis of cosmogony, to which we have just referred, and gave it
definite proportions; in fact, made it so thoroughly his own that posterity
will always link it with his name. Discarding the crude notions of cometary
impact and volcanic eruption, Laplace filled up the gaps in the hypothesis
with the aid of well-known laws of gravitation and motion. He assumed that
the primitive mass of cosmic matter which was destined to form our solar
system was revolving on its axis even at a time when it was still nebular in
character, and filled all space to a distance far beyond the present limits of
the system. As this vaporous mass contracted through loss of heat, it
revolved more and more swiftly, and from time to time, through balance of
forces at its periphery, rings of its substance were whirled off and left
revolving there, subsequently to become condensed into planets, and in
their turn whirl off minor rings that became moons. The main body of the
original mass remains in the present as the still contracting and rotating
body which we call the sun.
Let us allow Laplace to explain all this in detail:
"In order to explain the prime movements of the planetary system," he
says, "there are the five following phenomena: The movement of the
planets in the same direction and very nearly in the same plane; the
movement of the satellites in the same direction as that of the planets; the
rotation of these different bodies and the sun in the same direction as their
revolution, and in nearly the same plane; the slight eccentricity of the orbits
of the planets and of the satellites; and, finally, the great eccentricity of the
orbits of the comets, as if their inclinations had been left to chance.

"Buffon is the only man I know who, since the discovery of the true
system of the world, has endeavored to show the origin of the planets and
their satellites. He supposes that a comet, in falling into the sun, drove from
it a mass of matter which was reassembled at a distance in the form of
various globes more or less large, and more or less removed from the sun,
and that these globes, becoming opaque and solid, are now the planets and
their satellites.
"This hypothesis satisfies the first of the five preceding phenomena; for it
is clear that all the bodies thus formed would move very nearly in the plane
which passed through the centre of the sun, and in the direction of the
torrent of matter which was produced; but the four other phenomena appear
to be inexplicable to me by this means. Indeed, the absolute movement of
the molecules of a planet ought then to be in the direction of the movement
of its centre of gravity; but it does not at all follow that the motion of the
rotation of the planets should be in the same direction. Thus the earth
should rotate from east to west, but nevertheless the absolute movement of
its molecules should be from east to west; and this ought also to apply to the
movement of the revolution of the satellites, in which the direction,
according to the hypothesis which he offers, is not necessarily the same as
that of the progressive movement of the planets.
"A phenomenon not only very difficult to explain under this hypothesis,
but one which is even contrary to it, is the slight eccentricity of the
planetary orbits. We know, by the theory of central forces, that if a body
moves in a closed orbit around the sun and touches it, it also always comes
back to that point at every revolution; whence it follows that if the planets
were originally detached from the sun, they would touch it at each return
towards it, and their orbits, far from being circular, would be very eccentric.
It is true that a mass of matter driven from the sun cannot be exactly
compared to a globe which touches its surface, for the impulse which the
particles of this mass receive from one another and the reciprocal attractions
which they exert among themselves, could, in changing the direction of
their movements, remove their perihelions from the sun; but their orbits
would be always most eccentric, or at least they would not have slight
eccentricities except by the most extraordinary chance. Thus we cannot see,
according to the hypothesis of Buffon, why the orbits of more than a
hundred comets already observed are so elliptical. This hypothesis is

therefore very far from satisfying the preceding phenomena. Let us see if it
is possible to trace them back to their true cause.
"Whatever may be its ultimate nature, seeing that it has caused or
modified the movements of the planets, it is necessary that this cause should
embrace every body, and, in view of the enormous distances which separate
them, it could only have been a fluid of immense extent. In order to have
given them an almost circular movement in the same direction around the
sun, it is necessary that this fluid should have enveloped the sun as in an
atmosphere. The consideration of the planetary movements leads us then to
think that, on account of excessive heat, the atmosphere of the sun
originally extended beyond the orbits of all the planets, and that it was
successively contracted to its present limits.
"In the primitive condition in which we suppose the sun to have been, it
resembled a nebula such as the telescope shows is composed of a nucleus
more or less brilliant, surrounded by a nebulosity which, on condensing
itself towards the centre, forms a star. If it is conceived by analogy that all
the stars were formed in this manner, it is possible to imagine their previous
condition of nebulosity, itself preceded by other states in which the
nebulous matter was still more diffused, the nucleus being less and less
luminous. By going back as far as possible, we thus arrive at a nebulosity so
diffused that its existence could hardly be suspected.
"For a long time the peculiar disposition of certain stars, visible to the
unaided eye, has struck philosophical observers. Mitchell has already
remarked how little probable it is that the stars in the Pleiades, for example,
could have been contracted into the small space which encloses them by the
fortuity of chance alone, and he has concluded that this group of stars, and
similar groups which the skies present to us, are the necessary result of the
condensation of a nebula, with several nuclei, and it is evident that a nebula,
by continually contracting, towards these various nuclei, at length would
form a group of stars similar to the Pleiades. The condensation of a nebula
with two nuclei would form a system of stars close together, turning one
upon the other, such as those double stars of which we already know the
respective movements.
"But how did the solar atmosphere determine the movements of the
rotation and revolution of the planets and satellites? If these bodies had
penetrated very deeply into this atmosphere, its resistance would have

caused them to fall into the sun. We can therefore conjecture that the planets
were formed at their successive limits by the condensation of a zone of
vapors which the sun, on cooling, left behind, in the plane of his equator.
"Let us recall the results which we have given in a preceding chapter. The
atmosphere of the sun could not have extended indefinitely. Its limit was the
point where the centrifugal force due to its movement of rotation balanced
its weight. But in proportion as the cooling contracted the atmosphere, and
those molecules which were near to them condensed upon the surface of the
body, the movement of the rotation increased; for, on account of the Law of
Areas, the sum of the areas described by the vector of each molecule of the
sun and its atmosphere and projected in the plane of the equator being
always the same, the rotation should increase when these molecules
approach the centre of the sun. The centrifugal force due to this movement
becoming thus larger, the point where the weight is equal to it is nearer the
sun. Supposing, then, as it is natural to admit, that the atmosphere extended
at some period to its very limits, it should, on cooling, leave molecules
behind at this limit and at limits successively occasioned by the increased
rotation of the sun. The abandoned molecules would continue to revolve
around this body, since their centrifugal force was balanced by their weight.
But this equilibrium not arising in regard to the atmospheric molecules
parallel to the solar equator, the latter, on account of their weight,
approached the atmosphere as they condensed, and did not cease to belong
to it until by this motion they came upon the equator.
"Let us consider now the zones of vapor successively left behind. These
zones ought, according to appearance, by the condensation and mutual
attraction of their molecules, to form various concentric rings of vapor
revolving around the sun. The mutual gravitational friction of each ring
would accelerate some and retard others, until they had all acquired the
same angular velocity. Thus the actual velocity of the molecules most
removed from the sun would be the greatest. The following cause would
also operate to bring about this difference of speed. The molecules farthest
from the sun, and which by the effects of cooling and condensation
approached one another to form the outer part of the ring, would have
always described areas proportional to the time since the central force by
which they were controlled has been constantly directed towards this body.
But this constancy of areas necessitates an increase of velocity proportional

to the distance. It is thus seen that the same cause would diminish the
velocity of the molecules which form the inner part of the ring.
"If all the molecules of the ring of vapor continued to condense without
disuniting, they would at length form a ring either solid or fluid. But this
formation would necessitate such a regularity in every part of the ring, and
in its cooling, that this phenomenon is extremely rare; and the solar system
affords us, indeed, but one example—namely, in the ring of Saturn. In
nearly every case the ring of vapor was broken into several masses, each
moving at similar velocities, and continuing to rotate at the same distance
around the sun. These masses would take a spheroid form with a rotatory
movement in the direction of the revolution, because their inner molecules
had less velocity than the outer. Thus were formed so many planets in a
condition of vapor. But if one of them were powerful enough to reunite
successively by its attraction all the others around its centre of gravity, the
ring of vapor would be thus transformed into a single spheroidical mass of
vapor revolving around the sun with a rotation in the direction of its
revolution. The latter case has been that which is the most common, but
nevertheless the solar system affords us an instance of the first case in the
four small planets which move between Jupiter and Mars; at least, if we do
not suppose, as does M. Olbers, that they originally formed a single planet
which a mighty explosion broke up into several portions each moving at
different velocities.
"According to our hypothesis, the comets are strangers to our planetary
system. In considering them, as we have done, as minute nebulosities,
wandering from solar system to solar system, and formed by the
condensation of the nebulous matter everywhere existent in profusion in the
universe, we see that when they come into that part of the heavens where
the sun is all-powerful, he forces them to describe orbits either elliptical or
hyperbolic, their paths being equally possible in all directions, and at all
inclinations of the ecliptic, conformably to what has been observed. Thus
the condensation of nebulous matter, by which we have at first explained
the motions of the rotation and revolution of the planets and their satellites
in the same direction, and in nearly approximate planes, explains also why
the movements of the comets escape this general law."(3)
The nebular hypothesis thus given detailed completion by Laplace is a
worthy complement of the grand cosmologic scheme of Herschel. Whether

true or false, the two conceptions stand as the final contributions of the
eighteenth century to the history of man's ceaseless efforts to solve the
mysteries of cosmic origin and cosmic structure. The world listened eagerly
and without prejudice to the new doctrines; and that attitude tells of a
marvellous intellectual growth of our race. Mark the transition. In the year
1600, Bruno was burned at the stake for teaching that our earth is not the
centre of the universe. In 1700, Newton was pronounced "impious and
heretical" by a large school of philosophers for declaring that the force
which holds the planets in their orbits is universal gravitation. In 1800,
Laplace and Herschel are honored for teaching that gravitation built up the
system which it still controls; that our universe is but a minor nebula, our
sun but a minor star, our earth a mere atom of matter, our race only one of
myriad races peopling an infinity of worlds. Doctrines which but the span
of two human lives before would have brought their enunciators to the stake
were now pronounced not impious, but sublime.
ASTEROIDS AND SATELLITES
The first day of the nineteenth century was fittingly signalized by the
discovery of a new world. On the evening of January 1, 1801, an Italian
astronomer, Piazzi, observed an apparent star of about the eighth magnitude
(hence, of course, quite invisible to the unaided eye), which later on was
seen to have moved, and was thus shown to be vastly nearer the earth than
any true star. He at first supposed, as Herschel had done when he first saw
Uranus, that the unfamiliar body was a comet; but later observation proved
it a tiny planet, occupying a position in space between Mars and Jupiter. It
was christened Ceres, after the tutelary goddess of Sicily.
Though unpremeditated, this discovery was not unexpected, for
astronomers had long surmised the existence of a planet in the wide gap
between Mars and Jupiter. Indeed, they were even preparing to make
concerted search for it, despite the protests of philosophers, who argued that
the planets could not possibly exceed the magic number seven, when Piazzi
forestalled their efforts. But a surprise came with the sequel; for the very
next year Dr. Olbers, the wonderful physician-astronomer of Bremen, while
following up the course of Ceres, happened on another tiny moving star,
similarly located, which soon revealed itself as planetary. Thus two planets
were found where only one was expected.

The existence of the supernumerary was a puzzle, but Olbers solved it for
the moment by suggesting that Ceres and Pallas, as he called his captive,
might be fragments of a quondam planet, shattered by internal explosion or
by the impact of a comet. Other similar fragments, he ventured to predict,
would be found when searched for. William Herschel sanctioned this theory,
and suggested the name asteroids for the tiny planets. The explosion theory
was supported by the discovery of another asteroid, by Harding, of
Lilienthal, in 1804, and it seemed clinched when Olbers himself found a
fourth in 1807. The new-comers were named Juno and Vesta respectively.
There the case rested till 1845, when a Prussian amateur astronomer
named Hencke found another asteroid, after long searching, and opened a
new epoch of discovery. From then on the finding of asteroids became a
commonplace. Latterly, with the aid of photography, the list has been
extended to above four hundred, and as yet there seems no dearth in the
supply, though doubtless all the larger members have been revealed. Even
these are but a few hundreds of miles in diameter, while the smaller ones
are too tiny for measurement. The combined bulk of these minor planets is
believed to be but a fraction of that of the earth.
Olbers's explosion theory, long accepted by astronomers, has been proven
open to fatal objections. The minor planets are now believed to represent a
ring of cosmical matter, cast off from the solar nebula like the rings that
went to form the major planets, but prevented from becoming aggregated
into a single body by the perturbing mass of Jupiter.
The Discovery of Neptune
As we have seen, the discovery of the first asteroid confirmed a
conjecture; the other important planetary discovery of the nineteenth
century fulfilled a prediction. Neptune was found through scientific
prophecy. No one suspected the existence of a trans-Uranian planet till
Uranus itself, by hair-breadth departures from its predicted orbit, gave out
the secret. No one saw the disturbing planet till the pencil of the
mathematician, with almost occult divination, had pointed out its place in
the heavens. The general predication of a trans-Uranian planet was made by
Bessel, the great Konigsberg astronomer, in 1840; the analysis that revealed
its exact location was undertaken, half a decade later, by two independent
workers—John Couch Adams, just graduated senior wrangler at

Cambridge, England, and U. J. J. Leverrier, the leading French
mathematician of his generation.
Adams's calculation was first begun and first completed. But it had one
radical defect—it was the work of a young and untried man. So it found
lodgment in a pigeon-hole of the desk of England's Astronomer Royal, and
an opportunity was lost which English astronomers have never ceased to
mourn. Had the search been made, an actual planet would have been seen
shining there, close to the spot where the pencil of the mathematician had
placed its hypothetical counterpart. But the search was not made, and while
the prophecy of Adams gathered dust in that regrettable pigeon-hole,
Leverrier's calculation was coming on, his tentative results meeting full
encouragement from Arago and other French savants. At last the laborious
calculations proved satisfactory, and, confident of the result, Leverrier sent
to the Berlin observatory, requesting that search be made for the disturber of
Uranus in a particular spot of the heavens. Dr. Galle received the request
September 23, 1846. That very night he turned his telescope to the indicated
region, and there, within a single degree of the suggested spot, he saw a
seeming star, invisible to the unaided eye, which proved to be the long-
sought planet, henceforth to be known as Neptune. To the average mind,
which finds something altogether mystifying about abstract mathematics,
this was a feat savoring of the miraculous.
Stimulated by this success, Leverrier calculated an orbit for an interior
planet from perturbations of Mercury, but though prematurely christened
Vulcan, this hypothetical nursling of the sun still haunts the realm of the
undiscovered, along with certain equally hypothetical trans-Neptunian
planets whose existence has been suggested by "residual perturbations" of
Uranus, and by the movements of comets. No other veritable additions of
the sun's planetary family have been made in our century, beyond the
finding of seven small moons, which chiefly attest the advance in telescopic
powers. Of these, the tiny attendants of our Martian neighbor, discovered by
Professor Hall with the great Washington refractor, are of greatest interest,
because of their small size and extremely rapid flight. One of them is poised
only six thousand miles from Mars, and whirls about him almost four times
as fast as he revolves, seeming thus, as viewed by the Martian, to rise in the
west and set in the east, and making the month only one-fourth as long as
the day.

The Rings of Saturn
The discovery of the inner or crape ring of Saturn, made simultaneously
in 1850 by William C. Bond, at the Harvard observatory, in America, and
the Rev. W. R. Dawes in England, was another interesting optical
achievement; but our most important advances in knowledge of Saturn's
unique system are due to the mathematician. Laplace, like his predecessors,
supposed these rings to be solid, and explained their stability as due to
certain irregularities of contour which Herschel bad pointed out. But about
1851 Professor Peirce, of Harvard, showed the untenability of this
conclusion, proving that were the rings such as Laplace thought them they
must fall of their own weight. Then Professor J. Clerk-Maxwell, of
Cambridge, took the matter in hand, and his analysis reduced the puzzling
rings to a cloud of meteoric particles—a "shower of brickbats"—each
fragment of which circulates exactly as if it were an independent planet,
though of course perturbed and jostled more or less by its fellows. Mutual
perturbations, and the disturbing pulls of Saturn's orthodox satellites, as
investigated by Maxwell, explain nearly all the phenomena of the rings in a
manner highly satisfactory.
After elaborate mathematical calculations covering many pages of his
paper entitled "On the Stability of Saturn's Rings," he summarizes his
deductions as follows:
"Let us now gather together the conclusions we have been able to draw
from the mathematical theory of various kinds of conceivable rings.
"We found that the stability of the motion of a solid ring depended on so
delicate an adjustment, and at the same time so unsymmetrical a
distribution of mass, that even if the exact conditions were fulfilled, it could
scarcely last long, and, if it did, the immense preponderance of one side of
the ring would be easily observed, contrary to experience. These
considerations, with others derived from the mechanical structure of so vast
a body, compel us to abandon any theory of solid rings.
"We next examined the motion of a ring of equal satellites, and found
that if the mass of the planet is sufficient, any disturbances produced in the
arrangement of the ring will be propagated around it in the form of waves,
and will not introduce dangerous confusion. If the satellites are unequal, the
propagations of the waves will no longer be regular, but disturbances of the
ring will in this, as in the former case, produce only waves, and not growing

confusion. Supposing the ring to consist, not of a single row of large
satellites, but a cloud of evenly distributed unconnected particles, we found
that such a cloud must have a very small density in order to be permanent,
and that this is inconsistent with its outer and inner parts moving with the
same angular velocity. Supposing the ring to be fluid and continuous, we
found that it will be necessarily broken up into small portions.
"We conclude, therefore, that the rings must consist of disconnected
particles; these must be either solid or liquid, but they must be independent.
The entire system of rings must, therefore, consist either of a series of many
concentric rings each moving with its own velocity and having its own
system of waves, or else of a confused multitude of revolving particles not
arranged in rings and continually coming into collision with one another.
"Taking the first case, we found that in an indefinite number of possible
cases the mutual perturbations of two rings, stable in themselves, might
mount up in time to a destructive magnitude, and that such cases must
continually occur in an extensive system like that of Saturn, the only
retarding cause being the irregularity of the rings.
"The result of long-continued disturbance was found to be the spreading-
out of the rings in breadth, the outer rings pressing outward, while the inner
rings press inward.
"The final result, therefore, of the mechanical theory is that the only
system of rings which can exist is one composed of an indefinite number of
unconnected particles, revolving around the planet with different velocities,
according to their respective distances. These particles may be arranged in
series of narrow rings, or they may move through one another irregularly. In
the first case the destruction of the system will be very slow, in the second
case it will be more rapid, but there may be a tendency towards
arrangement in narrow rings which may retard the process.
"We are not able to ascertain by observation the constitution of the two
outer divisions of the system of rings, but the inner ring is certainly
transparent, for the limb of Saturn has been observed through it. It is also
certain that though the space occupied by the ring is transparent, it is not
through the material parts of it that the limb of Saturn is seen, for his limb
was observed without distortion; which shows that there was no refraction,
and, therefore, that the rays did not pass through a medium at all, but
between the solar or liquid particles of which the ring is composed. Here,

then, we have an optical argument in favor of the theory of independent
particles as the material of the rings. The two outer rings may be of the
same nature, but not so exceedingly rare that a ray of light can pass through
their whole thickness without encountering one of the particles.
"Finally, the two outer rings have been observed for two hundred years,
and it appears, from the careful analysis of all the observations of M.
Struve, that the second ring is broader than when first observed, and that its
inner edge is nearer the planet than formerly. The inner ring also is
suspected to be approaching the planet ever since its discovery in 1850.
These appearances seem to indicate the same slow progress of the rings
towards separation which we found to be the result of theory, and the
remark that the inner edge of the inner ring is more distinct seems to
indicate that the approach towards the planet is less rapid near the edge, as
we had reason to conjecture. As to the apparent unchangeableness of the
exterior diameter of the outer ring, we must remember that the outer rings
are certainly far more dense than the inner one, and that a small change in
the outer rings must balance a great change in the inner one. It is possible,
however, that some of the observed changes may be due to the existence of
a resisting medium. If the changes already suspected should be confirmed
by repeated observations with the same instruments, it will be worth while
to investigate more carefully whether Saturn's rings are permanent or
transitory elements of the solar system, and whether in that part of the
heavens we see celestial immutability or terrestrial corruption and
generation, and the old order giving place to the new before our eyes."(4)
Studies of the Moon
But perhaps the most interesting accomplishments of mathematical
astronomy—from a mundane standpoint, at any rate—are those that refer to
the earth's own satellite. That seemingly staid body was long ago
discovered to have a propensity to gain a little on the earth, appearing at
eclipses an infinitesimal moment ahead of time. Astronomers were sorely
puzzled by this act of insubordination; but at last Laplace and Lagrange
explained it as due to an oscillatory change in the earth's orbit, thus fully
exonerating the moon, and seeming to demonstrate the absolute stability of
our planetary system, which the moon's misbehavior had appeared to
threaten.

This highly satisfactory conclusion was an orthodox belief of celestial
mechanics until 1853, when Professor Adams of Neptunian fame, with
whom complex analyses were a pastime, reviewed Laplace's calculation,
and discovered an error which, when corrected, left about half the moon's
acceleration unaccounted for. This was a momentous discrepancy, which at
first no one could explain. But presently Professor Helmholtz, the great
German physicist, suggested that a key might be found in tidal friction,
which, acting as a perpetual brake on the earth's rotation, and affecting not
merely the waters but the entire substance of our planet, must in the long
sweep of time have changed its rate of rotation. Thus the seeming
acceleration of the moon might be accounted for as actual retardation of the
earth's rotation—a lengthening of the day instead of a shortening of the
month.
Again the earth was shown to be at fault, but this time the moon could
not be exonerated, while the estimated stability of our system, instead of
being re-established, was quite upset. For the tidal retardation is not an
oscillatory change which will presently correct itself, like the orbital
wobble, but a perpetual change, acting always in one direction. Unless fully
counteracted by some opposing reaction, therefore (as it seems not to be),
the effect must be cumulative, the ultimate consequences disastrous. The
exact character of these consequences was first estimated by Professor G.
H. Darwin in 1879. He showed that tidal friction, in retarding the earth,
must also push the moon out from the parent planet on a spiral orbit.
Plainly, then, the moon must formerly have been nearer the earth than at
present. At some very remote period it must have actually touched the earth;
must, in other words, have been thrown off from the then plastic mass of the
earth, as a polyp buds out from its parent polyp. At that time the earth was
spinning about in a day of from two to four hours.
Now the day has been lengthened to twenty-four hours, and the moon has
been thrust out to a distance of a quarter-million miles; but the end is not
yet. The same progress of events must continue, till, at some remote period
in the future, the day has come to equal the month, lunar tidal action has
ceased, and one face of the earth looks out always at the moon with that
same fixed stare which even now the moon has been brought to assume
towards her parent orb. Should we choose to take even greater liberties with
the future, it may be made to appear (though some astronomers dissent from
this prediction) that, as solar tidal action still continues, the day must finally

exceed the month, and lengthen out little by little towards coincidence with
the year; and that the moon meantime must pause in its outward flight, and
come swinging back on a descending spiral, until finally, after the lapse of
untold aeons, it ploughs and ricochets along the surface of the earth, and
plunges to catastrophic destruction.
But even though imagination pause far short of this direful culmination,
it still is clear that modern calculations, based on inexorable tidal friction,
suffice to revolutionize the views formerly current as to the stability of the
planetary system. The eighteenth-century mathematician looked upon this
system as a vast celestial machine which had been in existence about six
thousand years, and which was destined to run on forever. The analyst of to-
day computes both the past and the future of this system in millions instead
of thousands of years, yet feels well assured that the solar system offers no
contradiction to those laws of growth and decay which seem everywhere to
represent the immutable order of nature.
COMETS AND METEORS
Until the mathematician ferreted out the secret, it surely never could have
been suspected by any one that the earth's serene attendant,

"That orbed maiden, with white fire laden,
Whom mortals call the moon,"

could be plotting injury to her parent orb. But there is another inhabitant
of the skies whose purposes have not been similarly free from popular
suspicion. Needless to say I refer to the black sheep of the sidereal family,
that "celestial vagabond" the comet.
Time out of mind these wanderers have been supposed to presage war,
famine, pestilence, perhaps the destruction of the world. And little wonder.
Here is a body which comes flashing out of boundless space into our
system, shooting out a pyrotechnic tail some hundreds of millions of miles
in length; whirling, perhaps, through the very atmosphere of the sun at a
speed of three or four hundred miles a second; then darting off on a
hyperbolic orbit that forbids it ever to return, or an elliptical one that cannot
be closed for hundreds or thousands of years; the tail meantime pointing
always away from the sun, and fading to nothingness as the weird voyager
recedes into the spatial void whence it came. Not many times need the
advent of such an apparition coincide with the outbreak of a pestilence or

the death of a Caesar to stamp the race of comets as an ominous clan in the
minds of all superstitious generations.
It is true, a hard blow was struck at the prestige of these alleged
supernatural agents when Newton proved that the great comet of 1680
obeyed Kepler's laws in its flight about the sun; and an even harder one
when the same visitant came back in 1758, obedient to Halley's prediction,
after its three-quarters of a century of voyaging but in the abyss of space.
Proved thus to bow to natural law, the celestial messenger could no longer
fully, sustain its role. But long-standing notoriety cannot be lived down in a
day, and the comet, though proved a "natural" object, was still regarded as a
very menacing one for another hundred years or so. It remained for the
nineteenth century to completely unmask the pretender and show how
egregiously our forebears had been deceived.
The unmasking began early in the century, when Dr. Olbers, then the
highest authority on the subject, expressed the opinion that the spectacular
tail, which had all along been the comet's chief stock-in-trade as an earth-
threatener, is in reality composed of the most filmy vapors, repelled from
the cometary body by the sun, presumably through electrical action, with a
velocity comparable to that of light. This luminous suggestion was held
more or less in abeyance for half a century. Then it was elaborated by
Zollner, and particularly by Bredichin, of the Moscow observatory, into
what has since been regarded as the most plausible of cometary theories. It
is held that comets and the sun are similarly electrified, and hence mutually
repulsive. Gravitation vastly outmatches this repulsion in the body of the
comet, but yields to it in the case of gases, because electrical force varies
with the surface, while gravitation varies only with the mass. From study of
atomic weights and estimates of the velocity of thrust of cometary tails,
Bredichin concluded that the chief components of the various kinds of tails
are hydrogen, hydrocarbons, and the vapor of iron; and spectroscopic
analysis goes far towards sustaining these assumptions.
But, theories aside, the unsubstantialness of the comet's tail has been put
to a conclusive test. Twice during the nineteenth century the earth has
actually plunged directly through one of these threatening appendages—in
1819, and again in 1861, once being immersed to a depth of some three
hundred thousand miles in its substance. Yet nothing dreadful happened to
us. There was a peculiar glow in the atmosphere, so the more imaginative

observers thought, and that was all. After such fiascos the cometary train
could never again pose as a world-destroyer.
But the full measure of the comet's humiliation is not yet told. The
pyrotechnic tail, composed as it is of portions of the comet's actual
substance, is tribute paid the sun, and can never be recovered. Should the
obeisance to the sun be many times repeated, the train-forming material will
be exhausted, and the comet's chiefest glory will have departed. Such a fate
has actually befallen a multitude of comets which Jupiter and the other
outlying planets have dragged into our system and helped the sun to hold
captive here. Many of these tailless comets were known to the eighteenth-
century astronomers, but no one at that time suspected the true meaning of
their condition. It was not even known how closely some of them are
enchained until the German astronomer Encke, in 1822, showed that one
which he had rediscovered, and which has since borne his name, was
moving in an orbit so contracted that it must complete its circuit in about
three and a half years. Shortly afterwards another comet, revolving in a
period of about six years, was discovered by Biela, and given his name.
Only two more of these short-period comets were discovered during the
first half of last century, but latterly they have been shown to be a numerous
family. Nearly twenty are known which the giant Jupiter holds so close that
the utmost reach of their elliptical tether does not let them go beyond the
orbit of Saturn. These aforetime wanderers have adapted themselves
wonderfully to planetary customs, for all of them revolve in the same
direction with the planets, and in planes not wide of the ecliptic.
Checked in their proud hyperbolic sweep, made captive in a planetary
net, deprived of their trains, these quondam free-lances of the heavens are
now mere shadows of their former selves. Considered as to mere bulk, they
are very substantial shadows, their extent being measured in hundreds of
thousands of miles; but their actual mass is so slight that they are quite at
the mercy of the gravitation pulls of their captors. And worse is in store for
them. So persistently do sun and planets tug at them that they are doomed
presently to be torn into shreds.
Such a fate has already overtaken one of them, under the very eyes of the
astronomers, within the relatively short period during which these ill-fated
comets have been observed. In 1832 Biela's comet passed quite near the
earth, as astronomers measure distance, and in doing so created a panic on

our planet. It did no greater harm than that, of course, and passed on its way
as usual. The very next time it came within telescopic hail it was seen to
have broken into two fragments. Six years later these fragments were
separated by many millions of miles; and in 1852, when the comet was due
again, astronomers looked for it in vain. It had been completely shattered.
What had become of the fragments? At that time no one positively knew.
But the question was to be answered presently. It chanced that just at this
period astronomers were paying much attention to a class of bodies which
they had hitherto somewhat neglected, the familiar shooting-stars, or
meteors. The studies of Professor Newton, of Yale, and Professor Adams, of
Cambridge, with particular reference to the great meteor-shower of
November, 1866, which Professor Newton had predicted and shown to be
recurrent at intervals of thirty-three years, showed that meteors are not mere
sporadic swarms of matter flying at random, but exist in isolated swarms,
and sweep about the sun in regular elliptical orbits.
Presently it was shown by the Italian astronomer Schiaparelli that one of
these meteor swarms moves in the orbit of a previously observed comet,
and other coincidences of the kind were soon forthcoming. The conviction
grew that meteor swarms are really the debris of comets; and this
conviction became a practical certainty when, in November, 1872, the earth
crossed the orbit of the ill-starred Biela, and a shower of meteors came
whizzing into our atmosphere in lieu of the lost comet.
And so at last the full secret was out. The awe-inspiring comet, instead of
being the planetary body it had all along been regarded, is really nothing
more nor less than a great aggregation of meteoric particles, which have
become clustered together out in space somewhere, and which by jostling
one another or through electrical action become luminous. So widely are
the individual particles separated that the cometary body as a whole has
been estimated to be thousands of times less dense than the earth's
atmosphere at sea-level. Hence the ease with which the comet may be
dismembered and its particles strung out into streaming swarms.
So thickly is the space we traverse strewn with this cometary dust that the
earth sweeps up, according to Professor Newcomb's estimate, a million tons
of it each day. Each individual particle, perhaps no larger than a millet seed,
becomes a shooting-star, or meteor, as it burns to vapor in the earth's upper
atmosphere. And if one tiny planet sweeps up such masses of this cosmic

matter, the amount of it in the entire stretch of our system must be beyond
all estimate. What a story it tells of the myriads of cometary victims that
have fallen prey to the sun since first he stretched his planetary net across
the heavens!
THE FIXED STARS
When Biela's comet gave the inhabitants of the earth such a fright in
1832, it really did not come within fifty millions of miles of us. Even the
great comet through whose filmy tail the earth passed in 1861 was itself
fourteen millions of miles away. The ordinary mind, schooled to measure
space by the tiny stretches of a pygmy planet, cannot grasp the import of
such distances; yet these are mere units of measure compared with the vast
stretches of sidereal space. Were the comet which hurtles past us at a speed
of, say, a hundred miles a second to continue its mad flight unchecked
straight into the void of space, it must fly on its frigid way eight thousand
years before it could reach the very nearest of our neighbor stars; and even
then it would have penetrated but a mere arm's-length into the vistas where
lie the dozen or so of sidereal residents that are next beyond. Even to the
trained mind such distances are only vaguely imaginable. Yet the
astronomer of our century has reached out across this unthinkable void and
brought back many a secret which our predecessors thought forever beyond
human grasp.
A tentative assault upon this stronghold of the stars was being made by
Herschel at the beginning of the century. In 1802 that greatest of observing
astronomers announced to the Royal Society his discovery that certain
double stars had changed their relative positions towards one another since
he first carefully charted them twenty years before. Hitherto it had been
supposed that double stars were mere optical effects. Now it became clear
that some of them, at any rate, are true "binary systems," linked together
presumably by gravitation and revolving about one another. Halley had
shown, three-quarters of a century before, that the stars have an actual or
"proper" motion in space; Herschel himself had proved that the sun shares
this motion with the other stars. Here was another shift of place, hitherto
quite unsuspected, to be reckoned with by the astronomer in fathoming
sidereal secrets.
Double Stars

When John Herschel, the only son and the worthy successor of the great
astronomer, began star-gazing in earnest, after graduating senior wrangler at
Cambridge, and making two or three tentative professional starts in other
directions to which his versatile genius impelled him, his first extended
work was the observation of his father's double stars. His studies, in which
at first he had the collaboration of Mr. James South, brought to light scores
of hitherto unrecognized pairs, and gave fresh data for the calculation of the
orbits of those longer known. So also did the independent researches of F.
G. W. Struve, the enthusiastic observer of the famous Russian observatory
at the university of Dorpat, and subsequently at Pulkowa. Utilizing data
gathered by these observers, M. Savary, of Paris, showed, in 1827, that the
observed elliptical orbits of the double stars are explicable by the ordinary
laws of gravitation, thus confirming the assumption that Newton's laws
apply to these sidereal bodies. Henceforth there could be no reason to doubt
that the same force which holds terrestrial objects on our globe pulls at each
and every particle of matter throughout the visible universe.
The pioneer explorers of the double stars early found that the systems
into which the stars are linked are by no means confined to single pairs.
Often three or four stars are found thus closely connected into gravitation
systems; indeed, there are all gradations between binary systems and great
clusters containing hundreds or even thousands of members. It is known,
for example, that the familiar cluster of the Pleiades is not merely an optical
grouping, as was formerly supposed, but an actual federation of associated
stars, some two thousand five hundred in number, only a few of which are
visible to the unaided eve. And the more carefully the motions of the stars
are studied, the more evident it becomes that widely separated stars are
linked together into infinitely complex systems, as yet but little understood.
At the same time, all instrumental advances tend to resolve more and more
seemingly single stars into close pairs and minor clusters. The two
Herschels between them discovered some thousands of these close multiple
systems; Struve and others increased the list to above ten thousand; and Mr.
S. W. Burnham, of late years the most enthusiastic and successful of
double-star pursuers, added a thousand new discoveries while he was still
an amateur in astronomy, and by profession the stenographer of a Chicago
court. Clearly the actual number of multiple stars is beyond all present
estimate.

The elder Herschel's early studies of double stars were undertaken in the
hope that these objects might aid him in ascertaining the actual distance of a
star, through measurement of its annual parallax—that is to say, of the angle
which the diameter of the earth's orbit would subtend as seen from the star.
The expectation was not fulfilled. The apparent shift of position of a star as
viewed from opposite sides of the earth's orbit, from which the parallax
might be estimated, is so extremely minute that it proved utterly
inappreciable, even to the almost preternaturally acute vision of Herschel,
with the aid of any instrumental means then at command. So the problem of
star distance allured and eluded him to the end, and he died in 1822 without
seeing it even in prospect of solution. His estimate of the minimum distance
of the nearest star, based though it was on the fallacious test of apparent
brilliancy, was a singularly sagacious one, but it was at best a scientific
guess, not a scientific measurement.
The Distance of the Stars
Just about this time, however, a great optician came to the aid of the
astronomers. Joseph Fraunhofer perfected the refracting telescope, as
Herschel had perfected the reflector, and invented a wonderfully accurate
"heliometer," or sun-measurer. With the aid of these instruments the old and
almost infinitely difficult problem of star distance was solved. In 1838
Bessel announced from the Konigsberg observatory that he had succeeded,
after months of effort, in detecting and measuring the parallax of a star.
Similar claims had been made often enough before, always to prove
fallacious when put to further test; but this time the announcement carried
the authority of one of the greatest astronomers of the age, and scepticism
was silenced.
Nor did Bessel's achievement long await corroboration. Indeed, as so
often happens in fields of discovery, two other workers had almost
simultaneously solved the same problem—Struve at Pulkowa, where the
great Russian observatory, which so long held the palm over all others, had
now been established; and Thomas Henderson, then working at the Cape of
Good Hope, but afterwards the Astronomer Royal of Scotland. Henderson's
observations had actual precedence in point of time, but Bessel's
measurements were so much more numerous and authoritative that he has
been uniformly considered as deserving the chief credit of the discovery,
which priority of publication secured him.

By an odd chance, the star on which Henderson's observations were
made, and consequently the first star the parallax of which was ever
measured, is our nearest neighbor in sidereal space, being, indeed, some ten
billions of miles nearer than the one next beyond. Yet even this nearest star
is more than two hundred thousand times as remote from us as the sun. The
sun's light flashes to the earth in eight minutes, and to Neptune in about
three and a half hours, but it requires three and a half years to signal Alpha
Centauri. And as for the great majority of the stars, had they been blotted
out of existence before the Christian era, we of to-day should still receive
their light and seem to see them just as we do. When we look up to the sky,
we study ancient history; we do not see the stars as they ARE, but as they
WERE years, centuries, even millennia ago.
The information derived from the parallax of a star by no means halts
with the disclosure of the distance of that body. Distance known, the proper
motion of the star, hitherto only to be reckoned as so many seconds of arc,
may readily be translated into actual speed of progress; relative brightness
becomes absolute lustre, as compared with the sun; and in the case of the
double stars the absolute mass of the components may be computed from
the laws of gravitation. It is found that stars differ enormously among
themselves in all these regards. As to speed, some, like our sun, barely
creep through space—compassing ten or twenty miles a second, it is true,
yet even at that rate only passing through the equivalent of their own
diameter in a day. At the other extreme, among measured stars, is one that
moves two hundred miles a second; yet even this "flying star," as seen from
the earth, seems to change its place by only about three and a half lunar
diameters in a thousand years. In brightness, some stars yield to the sun,
while others surpass him as the arc-light surpasses a candle. Arcturus, the
brightest measured star, shines like two hundred suns; and even this giant
orb is dim beside those other stars which are so distant that their parallax
cannot be measured, yet which greet our eyes at first magnitude. As to
actual bulk, of which apparent lustre furnishes no adequate test, some stars
are smaller than the sun, while others exceed him hundreds or perhaps
thousands of times. Yet one and all, so distant are they, remain mere
disklike points of light before the utmost powers of the modern telescope.
Revelations of the Spectroscope

All this seems wonderful enough, but even greater things were in store.
In 1859 the spectroscope came upon the scene, perfected by Kirchhoff and
Bunsen, along lines pointed out by Fraunhofer almost half a century before.
That marvellous instrument, by revealing the telltale lines sprinkled across a
prismatic spectrum, discloses the chemical nature and physical condition of
any substance whose light is submitted to it, telling its story equally well,
provided the light be strong enough, whether the luminous substance be
near or far—in the same room or at the confines of space. Clearly such an
instrument must prove a veritable magic wand in the hands of the
astronomer.
Very soon eager astronomers all over the world were putting the
spectroscope to the test. Kirchhoff himself led the way, and Donati and
Father Secchi in Italy, Huggins and Miller in England, and Rutherfurd in
America, were the chief of his immediate followers. The results exceeded
the dreams of the most visionary. At the very outset, in 1860, it was shown
that such common terrestrial substances as sodium, iron, calcium,
magnesium, nickel, barium, copper, and zinc exist in the form of glowing
vapors in the sun, and very soon the stars gave up a corresponding secret.
Since then the work of solar and sidereal analysis has gone on steadily in
the hands of a multitude of workers (prominent among whom, in this
country, are Professor Young of Princeton, Professor Langley of
Washington, and Professor Pickering of Harvard), and more than half the
known terrestrial elements have been definitely located in the sun, while
fresh discoveries are in prospect.
It is true the sun also contains some seeming elements that are unknown
on the earth, but this is no matter for surprise. The modern chemist makes
no claim for his elements except that they have thus far resisted all human
efforts to dissociate them; it would be nothing strange if some of them,
when subjected to the crucible of the sun, which is seen to vaporize iron,
nickel, silicon, should fail to withstand the test. But again, chemistry has by
no means exhausted the resources of the earth's supply of raw material, and
the substance which sends its message from a star may exist undiscovered
in the dust we tread or in the air we breathe. In the year 1895 two new
terrestrial elements were discovered; but one of these had for years been
known to the astronomer as a solar and suspected as a stellar element, and
named helium because of its abundance in the sun. The spectroscope had
reached out millions of miles into space and brought back this new element,

and it took the chemist a score of years to discover that he had all along had
samples of the same substance unrecognized in his sublunary laboratory.
There is hardly a more picturesque fact than that in the entire history of
science.
But the identity in substance of earth and sun and stars was not more
clearly shown than the diversity of their existing physical conditions. It was
seen that sun and stars, far from being the cool, earthlike, habitable bodies
that Herschel thought them (surrounded by glowing clouds, and protected
from undue heat by other clouds), are in truth seething caldrons of fiery
liquid, or gas made viscid by condensation, with lurid envelopes of belching
flames. It was soon made clear, also, particularly by the studies of
Rutherfurd and of Secchi, that stars differ among themselves in exact
constitution or condition. There are white or Sirian stars, whose spectrum
revels in the lines of hydrogen; yellow or solar stars (our sun being the
type), showing various metallic vapors; and sundry red stars, with banded
spectra indicative of carbon compounds; besides the purely gaseous stars of
more recent discovery, which Professor Pickering had specially studied.
Zollner's famous interpretation of these diversities, as indicative of varying
stages of cooling, has been called in question as to the exact sequence it
postulates, but the general proposition that stars exist under widely varying
conditions of temperature is hardly in dispute.
The assumption that different star types mark varying stages of cooling
has the further support of modern physics, which has been unable to
demonstrate any way in which the sun's radiated energy may be restored, or
otherwise made perpetual, since meteoric impact has been shown to be—
under existing conditions, at any rate—inadequate. In accordance with the
theory of Helmholtz, the chief supply of solar energy is held to be
contraction of the solar mass itself; and plainly this must have its limits.
Therefore, unless some means as yet unrecognized is restoring the lost
energy to the stellar bodies, each of them must gradually lose its lustre, and
come to a condition of solidification, seeming sterility, and frigid darkness.
In the case of our own particular star, according to the estimate of Lord
Kelvin, such a culmination appears likely to occur within a period of five or
six million years.
The Astronomy of the Invisible

But by far the strongest support of such a forecast as this is furnished by
those stellar bodies which even now appear to have cooled to the final stage
of star development and ceased to shine. Of this class examples in miniature
are furnished by the earth and the smaller of its companion planets. But
there are larger bodies of the same type out in stellar space—veritable "dark
stars"—invisible, of course, yet nowadays clearly recognized.
The opening up of this "astronomy of the invisible" is another of the
great achievements of the nineteenth century, and again it is Bessel to
whom the honor of discovery is due. While testing his stars for parallax;
that astute observer was led to infer, from certain unexplained aberrations of
motion, that various stars, Sirius himself among the number, are
accompanied by invisible companions, and in 1840 he definitely predicated
the existence of such "dark stars." The correctness of the inference was
shown twenty years later, when Alvan Clark, Jr., the American optician,
while testing a new lens, discovered the companion of Sirius, which proved
thus to be faintly luminous. Since then the existence of other and quite
invisible star companions has been proved incontestably, not merely by
renewed telescopic observations, but by the curious testimony of the
ubiquitous spectroscope.
One of the most surprising accomplishments of that instrument is the
power to record the flight of a luminous object directly in the line of vision.
If the luminous body approaches swiftly, its Fraunhofer lines are shifted
from their normal position towards the violet end of the spectrum; if it
recedes, the lines shift in the opposite direction. The actual motion of stars
whose distance is unknown may be measured in this way. But in certain
cases the light lines are seen to oscillate on the spectrum at regular
intervals. Obviously the star sending such light is alternately approaching
and receding, and the inference that it is revolving about a companion is
unavoidable. From this extraordinary test the orbital distance, relative mass,
and actual speed of revolution of the absolutely invisible body may be
determined. Thus the spectroscope, which deals only with light, makes
paradoxical excursions into the realm of the invisible. What secrets may the
stars hope to conceal when questioned by an instrument of such
necromantic power?
But the spectroscope is not alone in this audacious assault upon the
strongholds of nature. It has a worthy companion and assistant in the

photographic film, whose efficient aid has been invoked by the astronomer
even more recently. Pioneer work in celestial photography was, indeed,
done by Arago in France and by the elder Draper in America in 1839, but
the results then achieved were only tentative, and it was not till forty years
later that the method assumed really important proportions. In 1880, Dr.
Henry Draper, at Hastings-on-the-Hudson, made the first successful
photograph of a nebula. Soon after, Dr. David Gill, at the Cape observatory,
made fine photographs of a comet, and the flecks of starlight on his plates
first suggested the possibilities of this method in charting the heavens.
Since then star-charting with the film has come virtually to supersede the
old method. A concerted effort is being made by astronomers in various
parts of the world to make a complete chart of the heavens, and before the
close of our century this work will be accomplished, some fifty or sixty
millions of visible stars being placed on record with a degree of accuracy
hitherto unapproachable. Moreover, other millions of stars are brought to
light by the negative, which are too distant or dim to be visible with any
telescopic powers yet attained—a fact which wholly discredits all previous
inferences as to the limits of our sidereal system. Hence, notwithstanding
the wonderful instrumental advances of the nineteenth century, knowledge
of the exact form and extent of our universe seems more unattainable than it
seemed a century ago.
The Structure of Nebulae
Yet the new instruments, while leaving so much untold, have revealed
some vastly important secrets of cosmic structure. In particular, they have
set at rest the long-standing doubts as to the real structure and position of
the mysterious nebulae—those lazy masses, only two or three of them
visible to the unaided eye, which the telescope reveals in almost limitless
abundance, scattered everywhere among the stars, but grouped in particular
about the poles of the stellar stream or disk which we call the Milky Way.
Herschel's later view, which held that some at least of the nebulae are
composed of a "shining fluid," in process of condensation to form stars, was
generally accepted for almost half a century. But in 1844, when Lord
Rosse's great six-foot reflector—the largest telescope ever yet constructed
—was turned on the nebulae, it made this hypothesis seem very doubtful.
Just as Galileo's first lens had resolved the Milky Way into stars, just as
Herschel had resolved nebulae that resisted all instruments but his own, so

Lord Rosse's even greater reflector resolved others that would not yield to
Herschel's largest mirror. It seemed a fair inference that with sufficient
power, perhaps some day to be attained, all nebulae would yield, hence that
all are in reality what Herschel had at first thought them—vastly distant
"island universes," composed of aggregations of stars, comparable to our
own galactic system.
But the inference was wrong; for when the spectroscope was first applied
to a nebula in 1864, by Dr. Huggins, it clearly showed the spectrum not of
discrete stars, but of a great mass of glowing gases, hydrogen among others.
More extended studies showed, it is true, that some nebulae give the
continuous spectrum of solids or liquids, but the different types intermingle
and grade into one another. Also, the closest affinity is shown between
nebulae and stars. Some nebulae are found to contain stars, singly or in
groups, in their actual midst; certain condensed "planetary" nebulae are
scarcely to be distinguished from stars of the gaseous type; and recently the
photographic film has shown the presence of nebulous matter about stars
that to telescopic vision differ in no respect from the generality of their
fellows in the galaxy. The familiar stars of the Pleiades cluster, for example,
appear on the negative immersed in a hazy blur of light. All in all, the
accumulated impressions of the photographic film reveal a prodigality of
nebulous matter in the stellar system not hitherto even conjectured.
And so, of course, all question of "island universes" vanishes, and the
nebulae are relegated to their true position as component parts of the one
stellar system—the one universe—that is open to present human inspection.
And these vast clouds of world-stuff have been found by Professor Keeler,
of the Lick observatory, to be floating through space at the starlike speed of
from ten to thirty-eight miles per second.
The linking of nebulae with stars, so clearly evidenced by all these
modern observations, is, after all, only the scientific corroboration of what
the elder Herschel's later theories affirmed. But the nebulae have other
affinities not until recently suspected; for the spectra of some of them are
practically identical with the spectra of certain comets. The conclusion
seems warranted that comets are in point of fact minor nebulae that are
drawn into our system; or, putting it otherwise, that the telescopic nebulae
are simply gigantic distant comets.
Lockyer's Meteoric Hypothesis

Following up the surprising clews thus suggested, Sir Norman Lockyer,
of London, has in recent years elaborated what is perhaps the most
comprehensive cosmogonic guess that has ever been attempted. His theory,
known as the "meteoric hypothesis," probably bears the same relation to the
speculative thought of our time that the nebular hypothesis of Laplace bore
to that of the eighteenth century. Outlined in a few words, it is an attempt to
explain all the major phenomena of the universe as due, directly or
indirectly, to the gravitational impact of such meteoric particles, or specks
of cosmic dust, as comets are composed of. Nebulae are vast cometary
clouds, with particles more or less widely separated, giving off gases
through meteoric collisions, internal or external, and perhaps glowing also
with electrical or phosphorescent light. Gravity eventually brings the
nebular particles into closer aggregations, and increased collisions finally
vaporize the entire mass, forming planetary nebulae and gaseous stars.
Continued condensation may make the stellar mass hotter and more
luminous for a time, but eventually leads to its liquefaction, and ultimate
consolidation—the aforetime nebulae becoming in the end a dark or
planetary star.
The exact correlation which Lockyer attempts to point out between
successive stages of meteoric condensation and the various types of
observed stellar bodies does not meet with unanimous acceptance. Mr.
Ranyard, for example, suggests that the visible nebulae may not be nascent
stars, but emanations from stars, and that the true pre-stellar nebulae are
invisible until condensed to stellar proportions. But such details aside, the
broad general hypothesis that all the bodies of the universe are, so to speak,
of a single species—that nebulae (including comets), stars of all types, and
planets, are but varying stages in the life history of a single race or type of
cosmic organisms—is accepted by the dominant thought of our time as
having the highest warrant of scientific probability.
All this, clearly, is but an amplification of that nebular hypothesis which,
long before the spectroscope gave us warrant to accurately judge our
sidereal neighbors, had boldly imagined the development of stars out of
nebulae and of planets out of stars. But Lockyer's hypothesis does not stop
with this. Having traced the developmental process from the nebular to the
dark star, it sees no cause to abandon this dark star to its fate by assuming,
as the original speculation assumed, that this is a culminating and final
stage of cosmic existence. For the dark star, though its molecular activities

have come to relative stability and impotence, still retains the enormous
potentialities of molar motion; and clearly, where motion is, stasis is not.
Sooner or later, in its ceaseless flight through space, the dark star must
collide with some other stellar body, as Dr. Croll imagines of the dark
bodies which his "pre-nebular theory" postulates. Such collision may be
long delayed; the dark star may be drawn in comet-like circuit about
thousands of other stellar masses, and be hurtled on thousands of diverse
parabolic or elliptical orbits, before it chances to collide—but that matters
not: "billions are the units in the arithmetic of eternity," and sooner or later,
we can hardly doubt, a collision must occur. Then without question the
mutual impact must shatter both colliding bodies into vapor, or vapor
combined with meteoric fragments; in short, into a veritable nebula, the
matrix of future worlds. Thus the dark star, which is the last term of one
series of cosmic changes, becomes the first term of another series—at once
a post-nebular and a pre-nebular condition; and the nebular hypothesis, thus
amplified, ceases to be a mere linear scale, and is rounded out to connote an
unending series of cosmic cycles, more nearly satisfying the imagination.
In this extended view, nebulae and luminous stars are but the infantile
and adolescent stages of the life history of the cosmic individual; the dark
star, its adult stage, or time of true virility. Or we may think of the shrunken
dark star as the germ-cell, the pollen-grain, of the cosmic organism.
Reduced in size, as becomes a germ-cell, to a mere fraction of the nebular
body from which it sprang, it yet retains within its seemingly non-vital body
all the potentialities of the original organism, and requires only to blend
with a fellow-cell to bring a new generation into being. Thus may the
cosmic race, whose aggregate census makes up the stellar universe, be
perpetuated—individual solar systems, such as ours, being born, and
growing old, and dying to live again in their descendants, while the
universe as a whole maintains its unified integrity throughout all these
internal mutations—passing on, it may be, by infinitesimal stages, to a
culmination hopelessly beyond human comprehension.

III. THE NEW SCIENCE OF PALEONTOLOGY
WILLIAM SMITH AND FOSSIL SHELLS
Ever since Leonardo da Vinci first recognized the true character of
fossils, there had been here and there a man who realized that the earth's
rocky crust is one gigantic mausoleum. Here and there a dilettante had filled
his cabinets with relics from this monster crypt; here and there a
philosopher had pondered over them—questioning whether perchance they
had once been alive, or whether they were not mere abortive souvenirs of
that time when the fertile matrix of the earth was supposed to have

"teemed at a birth
Innumerous living creatures, perfect forms,
Limbed and full grown."

Some few of these philosophers—as Robert Hooke and Steno in the
seventeenth century, and Moro, Leibnitz, Buffon, Whitehurst, Werner,
Hutton, and others in the eighteenth—had vaguely conceived the
importance of fossils as records of the earth's ancient history, but the wisest
of them no more suspected the full import of the story written in the rocks
than the average stroller in a modern museum suspects the meaning of the
hieroglyphs on the case of a mummy.
It was not that the rudiments of this story are so very hard to decipher—
though in truth they are hard enough—but rather that the men who made the
attempt had all along viewed the subject through an atmosphere of
preconception, which gave a distorted image. Before this image could be
corrected it was necessary that a man should appear who could see without
prejudice, and apply sound common-sense to what he saw. And such a man
did appear towards the close of the century, in the person of William Smith,
the English surveyor. He was a self-taught man, and perhaps the more
independent for that, and he had the gift, besides his sharp eyes and
receptive mind, of a most tenacious memory. By exercising these faculties,
rare as they are homely, he led the way to a science which was destined, in
its later developments, to shake the structure of established thought to its
foundations.

Little enough did William Smith suspect, however, that any such dire
consequences were to come of his act when he first began noticing the
fossil shells that here and there are to be found in the stratified rocks and
soils of the regions over which his surveyor's duties led him. Nor, indeed,
was there anything of such apparent revolutionary character in the facts
which he unearthed; yet in their implications these facts were the most
disconcerting of any that had been revealed since the days of Copernicus
and Galileo. In its bald essence, Smith's discovery was simply this: that the
fossils in the rocks, instead of being scattered haphazard, are arranged in
regular systems, so that any given stratum of rock is labelled by its fossil
population; and that the order of succession of such groups of fossils is
always the same in any vertical series of strata in which they occur. That is
to say, if fossil A underlies fossil B in any given region, it never overlies it
in any other series; though a kind of fossils found in one set of strata may
be quite omitted in another. Moreover, a fossil once having disappeared
never reappears in any later stratum.
From these novel facts Smith drew the commonsense inference that the
earth had had successive populations of creatures, each of which in its turn
had become extinct. He partially verified this inference by comparing the
fossil shells with existing species of similar orders, and found that such as
occur in older strata of the rocks had no counterparts among living species.
But, on the whole, being eminently a practical man, Smith troubled himself
but little about the inferences that might be drawn from his facts. He was
chiefly concerned in using the key he had discovered as an aid to the
construction of the first geological map of England ever attempted, and he
left to others the untangling of any snarls of thought that might seem to
arise from his discovery of the succession of varying forms of life on the
globe.
He disseminated his views far and wide, however, in the course of his
journeyings—quite disregarding the fact that peripatetics went out of
fashion when the printing-press came in—and by the beginning of the
nineteenth century he had begun to have a following among the geologists
of England. It must not for a moment be supposed, however, that his
contention regarding the succession of strata met with immediate or general
acceptance. On the contrary, it was most bitterly antagonized. For a long
generation after the discovery was made, the generality of men, prone as
always to strain at gnats and swallow camels, preferred to believe that the

fossils, instead of being deposited in successive ages, had been swept all at
once into their present positions by the current of a mighty flood—and that
flood, needless to say, the Noachian deluge. Just how the numberless
successive strata could have been laid down in orderly sequence to the
depth of several miles in one such fell cataclysm was indeed puzzling,
especially after it came to be admitted that the heaviest fossils were not
found always at the bottom; but to doubt that this had been done in some
way was rank heresy in the early days of the nineteenth century.
CUVIER AND FOSSIL VERTEBRATES
But once discovered, William Smith's unique facts as to the succession of
forms in the rocks would not down. There was one most vital point,
however, regarding which the inferences that seem to follow from these
facts needed verification—the question, namely, whether the disappearance
of a fauna from the register in the rocks really implies the extinction of that
fauna. Everything really depended upon the answer to that question, and
none but an accomplished naturalist could answer it with authority.
Fortunately, the most authoritative naturalist of the time, George Cuvier,
took the question in hand—not, indeed, with the idea of verifying any
suggestion of Smith's, but in the course of his own original studies—at the
very beginning of the century, when Smith's views were attracting general
attention.
Cuvier and Smith were exact contemporaries, both men having been born
in 1769, that "fertile year" which gave the world also Chateaubriand, Von
Humboldt, Wellington, and Napoleon. But the French naturalist was of very
different antecedents from the English surveyor. He was brilliantly
educated, had early gained recognition as a scientist, and while yet a young
man had come to be known as the foremost comparative anatomist of his
time. It was the anatomical studies that led him into the realm of fossils.
Some bones dug out of the rocks by workmen in a quarry were brought to
his notice, and at once his trained eye told him that they were different from
anything he had seen before. Hitherto such bones, when not entirely
ignored, had been for the most part ascribed to giants of former days, or
even to fallen angels. Cuvier soon showed that neither giants nor angels
were in question, but elephants of an unrecognized species. Continuing his
studies, particularly with material gathered from gypsum beds near Paris, he
had accumulated, by the beginning of the nineteenth century, bones of about

twenty-five species of animals that he believed to be different from any now
living on the globe.
The fame of these studies went abroad, and presently fossil bones poured
in from all sides, and Cuvier's conviction that extinct forms of animals are
represented among the fossils was sustained by the evidence of many
strange and anomalous forms, some of them of gigantic size. In 1816 the
famous Ossements Fossiles, describing these novel objects, was published,
and vertebrate paleontology became a science. Among other things of great
popular interest the book contained the first authoritative description of the
hairy elephant, named by Cuvier the mammoth, the remains of which bad
been found embedded in a mass of ice in Siberia in 1802, so wonderfully
preserved that the dogs of the Tungusian fishermen actually ate its flesh.
Bones of the same species had been found in Siberia several years before by
the naturalist Pallas, who had also found the carcass of a rhinoceros there,
frozen in a mud-bank; but no one then suspected that these were members
of an extinct population—they were supposed to be merely transported
relics of the flood.
Cuvier, on the other hand, asserted that these and the other creatures he
described had lived and died in the region where their remains were found,
and that most of them have no living representatives upon the globe. This,
to be sure, was nothing more than William Smith had tried all along to
establish regarding lower forms of life; but flesh and blood monsters appeal
to the imagination in a way quite beyond the power of mere shells; so the
announcement of Cuvier's discoveries aroused the interest of the entire
world, and the Ossements Fossiles was accorded a popular reception
seldom given a work of technical science—a reception in which the
enthusiastic approval of progressive geologists was mingled with the bitter
protests of the conservatives.
"Naturalists certainly have neither explored all the continents," said
Cuvier, "nor do they as yet even know all the quadrupeds of those parts
which have been explored. New species of this class are discovered from
time to time; and those who have not examined with attention all the
circumstances belonging to these discoveries may allege also that the
unknown quadrupeds, whose fossil bones have been found in the strata of
the earth, have hitherto remained concealed in some islands not yet

discovered by navigators, or in some of the vast deserts which occupy the
middle of Africa, Asia, the two Americas, and New Holland.
"But if we carefully attend to the kind of quadrupeds that have been
recently discovered, and to the circumstances of their discovery, we shall
easily perceive that there is very little chance indeed of our ever finding
alive those which have only been seen in a fossil state.
"Islands of moderate size, and at a considerable distance from the large
continents, have very few quadrupeds. These must have been carried to
them from other countries. Cook and Bougainville found no other
quadrupeds besides hogs and dogs in the South Sea Islands; and the largest
quadruped of the West India Islands, when first discovered, was the agouti,
a species of the cavy, an animal apparently between the rat and the rabbit.
"It is true that the great continents, as Asia, Africa, the two Americas, and
New Holland, have large quadrupeds, and, generally speaking, contain
species common to each; insomuch, that upon discovering countries which
are isolated from the rest of the world, the animals they contain of the class
of quadruped were found entirely different from those which existed in
other countries. Thus, when the Spaniards first penetrated into South
America, they did not find it to contain a single quadruped exactly the same
with those of Europe, Asia, and Africa. The puma, the jaguar, the tapir, the
capybara, the llama, or glama, and vicuna, and the whole tribe of sapajous,
were to them entirely new animals, of which they had not the smallest
idea....
"If there still remained any great continent to be discovered, we might
perhaps expect to be made acquainted with new species of large
quadrupeds, among which some might be found more or less similar to
those of which we find the exuviae in the bowels of the earth. But it is
merely sufficient to glance the eye over the maps of the world and observe
the innumerable directions in which navigators have traversed the ocean, in
order to be satisfied that there does not remain any large land to be
discovered, unless it may be situated towards the Antarctic Pole, where
eternal ice necessarily forbids the existence of animal life."(1)
Cuvier then points out that the ancients were well acquainted with
practically all the animals on the continents of Europe, Asia, and Africa
now known to scientists. He finds little grounds, therefore, for belief in the
theory that at one time there were monstrous animals on the earth which it

was necessary to destroy in order that the present fauna and men might
flourish. After reviewing these theories and beliefs in detail, he takes up his
Inquiry Respecting the Fabulous Animals of the Ancients. "It is easy," he
says, "to reply to the foregoing objections, by examining the descriptions
that are left us by the ancients of those unknown animals, and by inquiring
into their origins. Now that the greater number of these animals have an
origin, the descriptions given of them bear the most unequivocal marks; as
in almost all of them we see merely the different parts of known animals
united by an unbridled imagination, and in contradiction to every
established law of nature."(2)
Having shown how the fabulous monsters of ancient times and of foreign
nations, such as the Chinese, were simply products of the imagination,
having no prototypes in nature, Cuvier takes up the consideration of the
difficulty of distinguishing the fossil bones of quadrupeds.
We shall have occasion to revert to this part of Cuvier's paper in another
connection. Here it suffices to pass at once to the final conclusion that the
fossil bones in question are the remains of an extinct fauna, the like of
which has no present-day representation on the earth. Whatever its
implications, this conclusion now seemed to Cuvier to be fully established.
In England the interest thus aroused was sent to fever-heat in 1821 by the
discovery of abundant beds of fossil bones in the stalagmite-covered floor
of a cave at Kirkdale, Yorkshire which went to show that England, too, had
once had her share of gigantic beasts. Dr. Buckland, the incumbent of the
chair of geology at Oxford, and the most authoritative English geologist of
his day, took these finds in hand and showed that the bones belonged to a
number of species, including such alien forms as elephants, rhinoceroses,
hippopotami, and hyenas. He maintained that all of these creatures had
actually lived in Britain, and that the caves in which their bones were found
had been the dens of hyenas.
The claim was hotly disputed, as a matter of course. As late as 1827
books were published denouncing Buckland, doctor of divinity though he
was, as one who had joined in an "unhallowed cause," and reiterating the
old cry that the fossils were only remains of tropical species washed thither
by the deluge. That they were found in solid rocks or in caves offered no
difficulty, at least not to the fertile imagination of Granville Penn, the leader
of the conservatives, who clung to the old idea of Woodward and Cattcut

that the deluge had dissolved the entire crust of the earth to a paste, into
which the relics now called fossils had settled. The caves, said Mr. Penn,
are merely the result of gases given off by the carcasses during
decomposition—great air-bubbles, so to speak, in the pasty mass, becoming
caverns when the waters receded and the paste hardened to rocky
consistency.
But these and such-like fanciful views were doomed even in the day of
their utterance. Already in 1823 other gigantic creatures, christened
ichthyosaurus and plesiosaurus by Conybeare, had been found in deeper
strata of British rocks; and these, as well as other monsters whose remains
were unearthed in various parts of the world, bore such strange forms that
even the most sceptical could scarcely hope to find their counterparts
among living creatures. Cuvier's contention that all the larger vertebrates of
the existing age are known to naturalists was borne out by recent
explorations, and there seemed no refuge from the conclusion that the fossil
records tell of populations actually extinct. But if this were admitted, then
Smith's view that there have been successive rotations of population could
no longer be denied. Nor could it be in doubt that the successive faunas,
whose individual remains have been preserved in myriads, representing
extinct species by thousands and tens of thousands, must have required vast
periods of time for the production and growth of their countless
generations.
As these facts came to be generally known, and as it came to be
understood in addition that the very matrix of the rock in which fossils are
imbedded is in many cases one gigantic fossil, composed of the remains of
microscopic forms of life, common-sense, which, after all, is the final
tribunal, came to the aid of belabored science. It was conceded that the only
tenable interpretation of the record in the rocks is that numerous
populations of creatures, distinct from one another and from present forms,
have risen and passed away; and that the geologic ages in which these
creatures lived were of inconceivable length. The rank and file came thus,
with the aid of fossil records, to realize the import of an idea which James
Hutton, and here and there another thinker, had conceived with the swift
intuition of genius long before the science of paleontology came into
existence. The Huttonian proposition that time is long had been abundantly
established, and by about the close of the first third of the last century

geologists had begun to speak of "ages" and "untold aeons of time" with a
familiarity which their predecessors had reserved for days and decades.
CHARLES LYELL COMBATS CATASTROPHISM
And now a new question pressed for solution. If the earth has been
inhabited by successive populations of beings now extinct, how have all
these creatures been destroyed? That question, however, seemed to present
no difficulties. It was answered out of hand by the application of an old
idea. All down the centuries, whatever their varying phases of cosmogonic
thought, there had been ever present the idea that past times were not as
recent times; that in remote epochs the earth had been the scene of awful
catastrophes that have no parallel in "these degenerate days." Naturally
enough, this thought, embalmed in every cosmogonic speculation of
whatever origin, was appealed to in explanation of the destruction of these
hitherto unimagined hosts, which now, thanks to science, rose from their
abysmal slumber as incontestable, but also as silent and as thought-
provocative, as Sphinx or pyramid. These ancient hosts, it was said, have
been exterminated at intervals of odd millions of years by the recurrence of
catastrophes of which the Mosaic deluge is the latest, but perhaps not the
last.
This explanation had fullest warrant of scientific authority. Cuvier had
prefaced his classical work with a speculative disquisition whose very title
(Discours sur les Revolutions du Globe) is ominous of catastrophism, and
whose text fully sustains the augury. And Buckland, Cuvier's foremost
follower across the Channel, had gone even beyond the master, naming the
work in which he described the Kirkdale fossils, Reliquiae Diluvianae, or
Proofs of a Universal Deluge.
Both these authorities supposed the creatures whose remains they studied
to have perished suddenly in the mighty flood whose awful current, as they
supposed, gouged out the modern valleys and hurled great blocks of granite
broadcast over the land. And they invoked similar floods for the
extermination of previous populations.
It is true these scientific citations had met with only qualified approval at
the time of their utterance, because then the conservative majority of
mankind did not concede that there had been a plurality of populations or
revolutions; but now that the belief in past geologic ages had ceased to be a
heresy, the recurring catastrophes of the great paleontologists were accepted

with acclaim. For the moment science and tradition were at one, and there
was a truce to controversy, except indeed in those outlying skirmish-lines of
thought whither news from headquarters does not permeate till it has
become ancient history at its source.
The truce, however, was not for long. Hardly had contemporary thought
begun to adjust itself to the conception of past ages of incomprehensible
extent, each terminated by a catastrophe of the Noachian type, when a man
appeared who made the utterly bewildering assertion that the geological
record, instead of proving numerous catastrophic revolutions in the earth's
past history, gives no warrant to the pretensions of any universal
catastrophe whatever, near or remote.
This iconoclast was Charles Lyell, the Scotchman, who was soon to be
famous as the greatest geologist of his time. As a young man he had become
imbued with the force of the Huttonian proposition, that present causes are
one with those that produced the past changes of the globe, and he carried
that idea to what he conceived to be its logical conclusion. To his mind this
excluded the thought of catastrophic changes in either inorganic or organic
worlds.
But to deny catastrophism was to suggest a revolution in current thought.
Needless to say, such revolution could not be effected without a long
contest. For a score of years the matter was argued pro and con., often with
most unscientific ardor. A mere outline of the controversy would fill a
volume; yet the essential facts with which Lyell at last established his
proposition, in its bearings on the organic world, may be epitomized in a
few words. The evidence which seems to tell of past revolutions is the
apparently sudden change of fossils from one stratum to another of the
rocks. But Lyell showed that this change is not always complete. Some
species live on from one alleged epoch into the next. By no means all the
contemporaries of the mammoth are extinct, and numerous marine forms
vastly more ancient still have living representatives.
Moreover, the blanks between strata in any particular vertical series are
amply filled in with records in the form of thick strata in some
geographically distant series. For example, in some regions Silurian rocks
are directly overlaid by the coal measures; but elsewhere this sudden break
is filled in with the Devonian rocks that tell of a great "age of fishes." So
commonly are breaks in the strata in one region filled up in another that we

are forced to conclude that the record shown by any single vertical series is
of but local significance—telling, perhaps, of a time when that particular
sea-bed oscillated above the water-line, and so ceased to receive sediment
until some future age when it had oscillated back again. But if this be the
real significance of the seemingly sudden change from stratum to stratum,
then the whole case for catastrophism is hopelessly lost; for such breaks in
the strata furnish the only suggestion geology can offer of sudden and
catastrophic changes of wide extent.
Let us see how Lyell elaborates these ideas, particularly with reference to
the rotation of species.(2)
"I have deduced as a corollary," he says, "that the species existing at any
particular period must, in the course of ages, become extinct, one after the
other. 'They must die out,' to borrow an emphatic expression from Buffon,
'because Time fights against them.' If the views which I have taken are just,
there will be no difficulty in explaining why the habitations of so many
species are now restrained within exceeding narrow limits. Every local
revolution tends to circumscribe the range of some species, while it enlarges
that of others; and if we are led to infer that new species originate in one
spot only, each must require time to diffuse itself over a wide area. It will
follow, therefore, from the adoption of our hypothesis that the recent origin
of some species and the high antiquity of others are equally consistent with
the general fact of their limited distribution, some being local because they
have not existed long enough to admit of their wide dissemination; others,
because circumstances in the animate or inanimate world have occurred to
restrict the range within which they may once have obtained....
"If the reader should infer, from the facts laid before him, that the
successive extinction of animals and plants may be part of the constant and
regular course of nature, he will naturally inquire whether there are any
means provided for the repair of these losses? Is it possible as a part of the
economy of our system that the habitable globe should to a certain extent
become depopulated, both in the ocean and on the land, or that the variety
of species should diminish until some new era arrives when a new and
extraordinary effort of creative energy is to be displayed? Or is it possible
that new species can be called into being from time to time, and yet that so
astonishing a phenomenon can escape the naturalist?

"In the first place, it is obviously more easy to prove that a species once
numerously represented in a given district has ceased to be than that some
other which did not pre-exist had made its appearance—assuming always,
for reasons before stated, that single stocks only of each animal and plant
are originally created, and that individuals of new species did not suddenly
start up in many different places at once.
"So imperfect has the science of natural history remained down to our
own times that, within the memory of persons now living, the numbers of
known animals and plants have doubled, or even quadrupled, in many
classes. New and often conspicuous species are annually discovered in parts
of the old continent long inhabited by the most civilized nations. Conscious,
therefore, of the limited extent of our information, we always infer, when
such discoveries are made, that the beings in question bad previously
eluded our research, or had at least existed elsewhere, and only migrated at
a recent period into the territories where we now find them.
"What kind of proofs, therefore, could we reasonably expect to find of
the origin at a particular period of a new species?
"Perhaps, it may be said in reply, that within the last two or three
centuries some forest tree or new quadruped might have been observed to
appear suddenly in those parts of England or France which had been most
thoroughly investigated—that naturalists might have been able to show that
no such being inhabited any other region of the globe, and that there was no
tradition of anything similar having been observed in the district where it
had made its appearance.
"Now, although this objection may seem plausible, yet its force will be
found to depend entirely on the rate of fluctuation which we suppose to
prevail in the animal world, and on the proportions which such conspicuous
subjects of the animal and vegetable kingdoms bear to those which are less
known and escape our observation. There are perhaps more than a million
species of plants and animals, exclusive of the microscopic and infusory
animalcules, now inhabiting the terraqueous globe, so that if only one of
these were to become extinct annually, and one new one were to be every
year called into being, much more than a million of years might be required
to bring about a complete revolution of organic life.
"I am not hazarding at present any hypothesis as to the probable rate of
change, but none will deny that when the annual birth and the annual death

of one species on the globe is proposed as a mere speculation, this, at least,
is to imagine no slight degree of instability in the animate creation. If we
divide the surface of the earth into twenty regions of equal area, one of
these might comprehend a space of land and water about equal in
dimensions to Europe, and might contain a twentieth part of the million of
species which may be assumed to exist in the animal kingdom. In this
region one species only could, according to the rate of mortality before
assumed, perish in twenty years, or only five out of fifty thousand in the
course of a century. But as a considerable portion of the whole world
belongs to the aquatic classes, with which we have a very imperfect
acquaintance, we must exclude them from our consideration, and, if they
constitute half of the entire number, then one species only might be lost in
forty years among the terrestrial tribes. Now the mammalia, whether
terrestrial or aquatic, bear so small a proportion to other classes of animals,
forming less, perhaps, than a thousandth part of a whole, that, if the
longevity of species in the different orders were equal, a vast period must
elapse before it would come to the turn of this conspicuous class to lose one
of their number. If one species only of the whole animal kingdom died out
in forty years, no more than one mammifer might disappear in forty
thousand years, in a region of the dimensions of Europe.
"It is easy, therefore, to see that in a small portion of such an area, in
countries, for example, of the size of England and France, periods of much
greater duration must elapse before it would be possible to authenticate the
first appearance of one of the larger plants or animals, assuming the annual
birth and death of one species to be the rate of vicissitude in the animal
creation throughout the world."(3)
In a word, then, said Lyell, it becomes clear that the numberless species
that have been exterminated in the past have died out one by one, just as
individuals of a species die, not in vast shoals; if whole populations have
passed away, it has been not by instantaneous extermination, but by the
elimination of a species now here, now there, much as one generation
succeeds another in the life history of any single species. The causes which
have brought about such gradual exterminations, and in the long lapse of
ages have resulted in rotations of population, are the same natural causes
that are still in operation. Species have died out in the past as they are dying
out in the present, under influence of changed surroundings, such as altered

climate, or the migration into their territory of more masterful species. Past
and present causes are one—natural law is changeless and eternal.
Such was the essence of the Huttonian doctrine, which Lyell adopted and
extended, and with which his name will always be associated. Largely
through his efforts, though of course not without the aid of many other
workers after a time, this idea—the doctrine of uniformitarianism, it came
to be called—became the accepted dogma of the geologic world not long
after the middle of the nineteenth century. The catastrophists, after clinging
madly to their phantom for a generation, at last capitulated without terms:
the old heresy became the new orthodoxy, and the way was paved for a
fresh controversy.
THE ORIGIN OF SPECIES
The fresh controversy followed quite as a matter of course. For the idea
of catastrophism had not concerned the destruction of species merely, but
their introduction as well. If whole faunas had been extirpated suddenly,
new faunas had presumably been introduced with equal suddenness by
special creation; but if species die out gradually, the introduction of new
species may be presumed to be correspondingly gradual. Then may not the
new species of a later geological epoch be the modified lineal descendants
of the extinct population of an earlier epoch?
The idea that such might be the case was not new. It had been suggested
when fossils first began to attract conspicuous attention; and such sagacious
thinkers as Buffon and Kant and Goethe and Erasmus Darwin had been
disposed to accept it in the closing days of the eighteenth century. Then, in
1809, it had been contended for by one of the early workers in systematic
paleontology—Jean Baptiste Lamarck, who had studied the fossil shells
about Paris while Cuvier studied the vertebrates, and who had been led by
these studies to conclude that there had been not merely a rotation but a
progression of life on the globe. He found the fossil shells—the fossils of
invertebrates, as he himself had christened them—in deeper strata than
Cuvier's vertebrates; and he believed that there had been long ages when no
higher forms than these were in existence, and that in successive ages
fishes, and then reptiles, had been the highest of animate creatures, before
mammals, including man, appeared. Looking beyond the pale of his bare
facts, as genius sometimes will, he had insisted that these progressive

populations had developed one from another, under influence of changed
surroundings, in unbroken series.
Of course such a thought as this was hopelessly misplaced in a
generation that doubted the existence of extinct species, and hardly less so
in the generation that accepted catastrophism; but it had been kept alive by
here and there an advocate like Geoffrey Saint-Hilaire, and now the
banishment of catastrophism opened the way for its more respectful
consideration. Respectful consideration was given it by Lyell in each
recurring edition of his Principles, but such consideration led to its
unqualified rejection. In its place Lyell put forward a modified hypothesis
of special creation. He assumed that from time to time, as the extirpation of
a species had left room, so to speak, for a new species, such new species
had been created de novo; and he supposed that such intermittent,
spasmodic impulses of creation manifest themselves nowadays quite as
frequently as at any time in the past. He did not say in so many words that
no one need be surprised to-day were he to see a new species of deer, for
example, come up out of the ground before him, "pawing to get free," like
Milton's lion, but his theory implied as much. And that theory, let it be
noted, was not the theory of Lyell alone, but of nearly all his associates in
the geologic world. There is perhaps no other fact that will bring home to
one so vividly the advance in thought of our own generation as the
recollection that so crude, so almost unthinkable a conception could have
been the current doctrine of science less than half a century ago.
This theory of special creation, moreover, excluded the current doctrine
of uniformitarianism as night excludes day, though most thinkers of the
time did not seem to be aware of the incompatibility of the two ideas. It
may be doubted whether even Lyell himself fully realized it. If he did, he
saw no escape from the dilemma, for it seemed to him that the record in the
rocks clearly disproved the alternative Lamarckian hypothesis. And almost
with one accord the paleontologists of the time sustained the verdict. Owen,
Agassiz, Falconer, Barrande, Pictet, Forbes, repudiated the idea as
unqualifiedly as their great predecessor Cuvier had done in the earlier
generation. Some of them did, indeed, come to believe that there is
evidence of a progressive development of life in the successive ages, but no
such graded series of fossils had been discovered as would give
countenance to the idea that one species had ever been transformed into
another. And to nearly every one this objection seemed insuperable.

But in 1859 appeared a book which, though not dealing primarily with
paleontology, yet contained a chapter that revealed the geological record in
an altogether new light. The book was Charles Darwin's Origin of Species,
the chapter that wonderful citation of the "Imperfections of the Geological
Record." In this epoch-making chapter Darwin shows what conditions must
prevail in any given place in order that fossils shall be formed, how unusual
such conditions are, and how probable it is that fossils once imbedded in
sediment of a sea-bed will be destroyed by metamorphosis of the rocks, or
by denudation when the strata are raised above the water-level. Add to this
the fact that only small territories of the earth have been explored
geologically, he says, and it becomes clear that the paleontological record as
we now possess it shows but a mere fragment of the past history of
organisms on the earth. It is a history "imperfectly kept and written in a
changing dialect. Of this history we possess the last volume alone, relating
only to two or three countries. Of this volume only here and there a short
chapter has been preserved, and of each page only here and there a few
lines." For a paleontologist to dogmatize from such a record would be as
rash, he thinks, as "for a naturalist to land for five minutes on a barren point
of Australia and then discuss the number and range of its productions."
This citation of observations, which when once pointed out seemed
almost self-evident, came as a revelation to the geological world. In the
clarified view now possible old facts took on a new meaning. It was
recalled that Cuvier had been obliged to establish a new order for some of
the first fossil creatures he examined, and that Buckland had noted that the
nondescript forms were intermediate in structure between allied existing
orders. More recently such intermediate forms had been discovered over
and over; so that, to name but one example, Owen had been able, with the
aid of extinct species, to "dissolve by gradations the apparently wide
interval between the pig and the camel." Owen, moreover, had been led to
speak repeatedly of the "generalized forms" of extinct animals, and Agassiz
had called them "synthetic or prophetic types," these terms clearly implying
"that such forms are in fact intermediate or connecting links." Darwin
himself had shown some years before that the fossil animals of any
continent are closely related to the existing animals of that continent—
edentates predominating, for example, in South America, and marsupials in
Australia. Many observers had noted that recent strata everywhere show a
fossil fauna more nearly like the existing one than do more ancient strata;

and that fossils from any two consecutive strata are far more closely related
to each other than are the fossils of two remote formations, the fauna of
each geological formation being, indeed, in a wide view, intermediate
between preceding and succeeding faunas.
So suggestive were all these observations that Lyell, the admitted leader
of the geological world, after reading Darwin's citations, felt able to drop
his own crass explanation of the introduction of species and adopt the
transmutation hypothesis, thus rounding out the doctrine of
uniformitarianism to the full proportions in which Lamarck had conceived
it half a century before. Not all paleontologists could follow him at once, of
course; the proof was not yet sufficiently demonstrative for that; but all
were shaken in the seeming security of their former position, which is
always a necessary stage in the progress of thought. And popular interest in
the matter was raised to white heat in a twinkling.
So, for the third time in this first century of its existence, paleontology
was called upon to play a leading role in a controversy whose interest
extended far beyond the bounds of staid truth-seeking science. And the
controversy waged over the age of the earth had not been more bitter, that
over catastrophism not more acrimonious, than that which now raged over
the question of the transmutation of species. The question had implications
far beyond the bounds of paleontology, of course. The main evidence yet
presented had been drawn from quite other fields, but by common consent
the record in the rocks might furnish a crucial test of the truth or falsity of
the hypothesis. "He who rejects this view of the imperfections of the
geological record," said Darwin, "will rightly reject the whole theory."
With something more than mere scientific zeal, therefore, paleontologists
turned anew to the records in the rocks, to inquire what evidence in proof or
refutation might be found in unread pages of the "great stone book." And, as
might have been expected, many minds being thus prepared to receive new
evidence, such evidence was not long withheld.
FOSSIL MAN
Indeed, at the moment of Darwin's writing a new and very instructive
chapter of the geologic record was being presented to the public—a chapter
which for the first time brought man into the story. In 1859 Dr. Falconer, the
distinguished British paleontologist, made a visit to Abbeville, in the valley
of the Somme, incited by reports that for a decade before bad been sent out

from there by M. Boucher de Perthes. These reports had to do with the
alleged finding of flint implements, clearly the work of man, in undisturbed
gravel-beds, in the midst of fossil remains of the mammoth and other
extinct animals. What Falconer saw there and what came of his visit may
best be told in his own words:
"In September of 1856 I made the acquaintance of my distinguished
friend M. Boucher de Perthes," wrote Dr. Falconer, "on the introduction of
M. Desnoyers at Paris, when he presented to me the earlier volume of his
Antiquites celtiques, etc., with which I thus became acquainted for the first
time. I was then fresh from the examination of the Indian fossil remains of
the valley of the Jumna; and the antiquity of the human race being a subject
of interest to both, we conversed freely about it, each from a different point
of view. M. de Perthes invited me to visit Abbeville, in order to examine his
antediluvian collection, fossil and geological, gleaned from the valley of the
Somme. This I was unable to accomplish then, but I reserved it for a future
occasion.
"In October, 1856, having determined to proceed to Sicily, I arranged by
correspondence with M. Boucher de Perthes to visit Abbeville on my
journey through France. I was at the time in constant communication with
Mr. Prestwich about the proofs of the antiquity of the human race yielded
by the Broxham Cave, in which he took a lively interest; and I engaged to
communicate to him the opinions at which I should arrive, after my
examination of the Abbeville collection. M. de Perthes gave me the freest
access to his materials, with unreserved explanations of all the facts of the
case that had come under his observation; and having considered his
Menchecourt Section, taken with such scrupulous care, and identified the
molars of elephas primigenius, which he had exhumed with his own hands
deep in that section, along with flint weapons, presenting the same character
as some of those found in the Broxham Cave, I arrived at the conviction
that they were of contemporaneous age, although I was not prepared to go
along with M. de Perthes in all his inferences regarding the hieroglyphics
and in an industrial interpretation of the various other objects which he had
met with."(4)
That Dr. Falconer was much impressed by the collection of M. de Perthes
is shown in a communication which he sent at once to his friend Prestwich:

"I have been richly rewarded," he exclaims. "His collection of wrought
flint implements, and of the objects of every description associated with
them, far exceeds everything I expected to have seen, especially from a
single locality. He has made great additions, since the publication of his
first volume, in the second, which I now have by me. He showed me flint
hatchets which HE HAD DUG UP with his own hands, mixed
INDISCRIMINATELY with molars of elephas primigenius. I examined and
identified plates of the molars and the flint objects which were got along
with them. Abbeville is an out-of-the-way place, very little visited; and the
French savants who meet him in Paris laugh at Monsieur de Perthes and his
researches. But after devoting the greater part of a day to his vast collection,
I am perfectly satisfied that there is a great deal of fair presumptive
evidence in favor of many of his speculations regarding the remote
antiquity of these industrial objects and their association with animals now
extinct. M. Boucher's hotel is, from the ground floor to garret, a continued
museum, filled with pictures, mediaeval art, and Gaulish antiquities,
including antediluvian flint-knives, fossil-bones, etc. If, during next
summer, you should happen to be paying a visit to France, let me strongly
recommend you to come to Abbeville. I am sure you would be richly
rewarded."(5)
This letter aroused the interest of the English geologists, and in the spring
of 1859 Prestwich and Mr. (afterwards Sir John) Evans made a visit to
Abbeville to see the specimens and examine at first hand the evidences as
pointed out by Dr. Falconer. "The evidence yielded by the valley of the
Somme," continues Falconer, in speaking of this visit, "was gone into with
the scrupulous care and severe and exhaustive analysis which are
characteristic of Mr. Prestwich's researches. The conclusions to which he
was conducted were communicated to the Royal Society on May 12, 1859,
in his celebrated memoir, read on May 26th and published in the
Philosophical Transactions of 1860, which, in addition to researches made
in the valley of the Somme, contained an account of similar phenomena
presented by the valley of the Waveney, near Hoxne, in Suffolk. Mr. Evans
communicated to the Society of Antiquaries a memoir on the character and
geological position of the 'Flint Implements in the Drift,' which appeared in
the Archaeologia for 1860. The results arrived at by Mr. Prestwich were
expressed as follows:

"First. That the flint implements are the result of design and the work of
man.
"Second. That they are found in beds of gravel, sand, and clay, which
have never been artificially disturbed.
"Third. That they occur associated with the remains of land, fresh-water,
and marine testacea, of species now living, and most of them still common
in the same neighborhood, and also with the remains of various mammalia
—a few species now living, but more of extinct forms.
"Fourth. That the period at which their entombment took place was
subsequent to the bowlder-clay period, and to that extent post-glacial; and
also that it was among the latest in geological time—one apparently anterior
to the surface assuming its present form, so far as it regards some of the
minor features."(6)
These reports brought the subject of the very significant human fossils at
Abbeville prominently before the public; whereas the publications of the
original discoverer, Boucher de Perthes, bearing date of 1847, had been
altogether ignored. A new aspect was thus given to the current controversy.
As Dr. Falconer remarked, geology was now passing through the same
ordeal that astronomy passed in the age of Galileo. But the times were
changed since the day when the author of the Dialogues was humbled
before the Congregation of the Index, and now no Index Librorum
Prohibitorum could avail to hide from eager human eyes such pages of the
geologic story as Nature herself had spared. Eager searchers were turning
the leaves with renewed zeal everywhere, and with no small measure of
success. In particular, interest attached just at this time to a human skull
which Dr. Fuhlrott had discovered in a cave at Neanderthal two or three
years before—a cranium which has ever since been famous as the
Neanderthal skull, the type specimen of what modern zoologists are
disposed to regard as a distinct species of man, Homo neanderthalensis.
Like others of the same type since discovered at Spy, it is singularly simian
in character—low-arched, with receding forehead and enormous,
protuberant eyebrows. When it was first exhibited to the scientists at Berlin
by Dr. Fuhlrott, in 1857, its human character was doubted by some of the
witnesses; of that, however, there is no present question.
This interesting find served to recall with fresh significance some
observations that had been made in France and Belgium a long generation

earlier, but whose bearings had hitherto been ignored. In 1826 MM. Tournal
and Christol had made independent discoveries of what they believed to be
human fossils in the caves of the south of France; and in 1827 Dr.
Schmerling had found in the cave of Engis, in Westphalia, fossil bones of
even greater significance. Schmerling's explorations had been made with
the utmost care, and patience. At Engis he had found human bones,
including skulls, intermingled with those of extinct mammals of the
mammoth period in a way that left no doubt in his mind that all dated from
the same geological epoch. He bad published a full account of his
discoveries in an elaborate monograph issued in 1833.
But at that time, as it chanced, human fossils were under a ban as
effectual as any ever pronounced by canonical index, though of far different
origin. The oracular voice of Cuvier had declared against the authenticity of
all human fossils. Some of the bones brought him for examination the great
anatomist had pettishly pitched out of the window, declaring them fit only
for a cemetery, and that had settled the matter for a generation: the evidence
gathered by lesser workers could avail nothing against the decision
rendered at the Delphi of Science. But no ban, scientific or canonical, can
longer resist the germinative power of a fact, and so now, after three
decades of suppression, the truth which Cuvier had buried beneath the
weight of his ridicule burst its bonds, and fossil man stood revealed, if not
as a flesh-and-blood, at least as a skeletal entity.
The reception now accorded our prehistoric ancestor by the progressive
portion of the scientific world amounted to an ovation; but the unscientific
masses, on the other hand, notwithstanding their usual fondness for tracing
remote genealogies, still gave the men of Engis and Neanderthal the cold
shoulder. Nor were all of the geologists quite agreed that the
contemporaneity of these human fossils with the animals whose remains
had been mingled with them had been fully established. The bare possibility
that the bones of man and of animals that long preceded him had been
swept together into the eaves in successive ages, and in some mysterious
way intermingled there, was clung to by the conservatives as a last refuge.
But even this small measure of security was soon to be denied them, for in
1865 two associated workers, M. Edouard Lartet and Mr. Henry Christy, in
exploring the caves of Dordogne, unearthed a bit of evidence against which
no such objection could be urged. This momentous exhibit was a bit of
ivory, a fragment of the tusk of a mammoth, on which was scratched a rude

but unmistakable outline portrait of the mammoth itself. If all the evidence
as to man's antiquity before presented was suggestive merely, here at last
was demonstration; for the cave-dwelling man could not well have drawn
the picture of the mammoth unless he had seen that animal, and to admit
that man and the mammoth had been contemporaries was to concede the
entire case. So soon, therefore, as the full import of this most instructive
work of art came to be realized, scepticism as to man's antiquity was
silenced for all time to come.
In the generation that has elapsed since the first drawing of the cave-
dweller artist was discovered, evidences of the wide-spread existence of
man in an early epoch have multiplied indefinitely, and to-day the
paleontologist traces the history of our race back beyond the iron and
bronze ages, through a neolithic or polished-stone age, to a paleolithic or
rough-stone age, with confidence born of unequivocal knowledge. And he
looks confidently to the future explorer of the earth's fossil records to
extend the history back into vastly more remote epochs, for it is little
doubted that paleolithic man, the most ancient of our recognized
progenitors, is a modern compared to those generations that represented the
real childhood of our race.
THE FOSSIL-BEDS OF AMERICA
Coincidently with the discovery of these highly suggestive pages of the
geologic story, other still more instructive chapters were being brought to
light in America. It was found that in the Rocky Mountain region, in strata
found in ancient lake beds, records of the tertiary period, or age of
mammals, had been made and preserved with fulness not approached in any
other region hitherto geologically explored. These records were made
known mainly by Professors Joseph Leidy, O. C. Marsh, and E. D. Cope,
working independently, and more recently by numerous younger
paleontologists.
The profusion of vertebrate remains thus brought to light quite beggars
all previous exhibits in point of mere numbers. Professor Marsh, for
example, who was first in the field, found three hundred new tertiary
species between the years 1870 and 1876. Meanwhile, in cretaceous strata,
he unearthed remains of about two hundred birds with teeth, six hundred
pterodactyls, or flying dragons, some with a spread of wings of twenty-five
feet, and one thousand five hundred mosasaurs of the sea-serpent type,

some of them sixty feet or more in length. In a single bed of Jurassic rock,
not larger than a good-sized lecture-room, he found the remains of one
hundred and sixty individuals of mammals, representing twenty species and
nine genera; while beds of the same age have yielded three hundred reptiles,
varying from the size of a rabbit to sixty or eighty feet in length.
But the chief interest of these fossils from the West is not their number
but their nature; for among them are numerous illustrations of just such
intermediate types of organisms as must have existed in the past if the
succession of life on the globe has been an unbroken lineal succession. Here
are reptiles with bat-like wings, and others with bird-like pelves and legs
adapted for bipedal locomotion. Here are birds with teeth, and other
reptilian characters. In short, what with reptilian birds and birdlike reptiles,
the gap between modern reptiles and birds is quite bridged over. In a similar
way, various diverse mammalian forms, as the tapir, the rhinoceros, and the
horse, are linked together by fossil progenitors. And, most important of all,
Professor Marsh has discovered a series of mammalian remains, occurring
in successive geological epochs, which are held to represent beyond cavil
the actual line of descent of the modern horse; tracing the lineage of our
one-toed species back through two and three toed forms, to an ancestor in
the eocene or early tertiary that had four functional toes and the rudiment of
a fifth. This discovery is too interesting and too important not to be detailed
at length in the words of the discoverer.
Marsh Describes the Fossil Horse
"It is a well-known fact," says Professor Marsh, "that the Spanish
discoverers of America discovered no horses on this continent, and that the
modern horse (Equus caballus, Linn.) was subsequently introduced from the
Old World. It is, however, not so generally known that these animals had
formerly been abundant here, and that long before, in tertiary time, near
relatives of the horse, and probably his ancestors, existed in the far West in
countless numbers and in a marvellous variety of forms. The remains of
equine mammals, now known from the tertiary and quaternary deposits of
this country, already represent more than double the number of genera and
species hitherto found in the strata of the eastern hemisphere, and hence
afford most important aid in tracing out the genealogy of the horses still
existing.

"The animals of this group which lived in America during the three
diversions of the tertiary period were especially numerous in the Rocky
Mountain regions, and their remains are well preserved in the old lake
basins which then covered so much of that country. The most ancient of
these lakes—which extended over a considerable part of the present
territories of Wyoming and Utah—remained so long in eocene times that
the mud and sand, slowly deposited in it, accumulated to more than a mile
in vertical thickness. In these deposits vast numbers of tropical animals
were entombed, and here the oldest equine remains occur, four species of
which have been described. These belong to the genus Orohippus (Marsh),
and are all of a diminutive size, hardly bigger than a fox. The skeletons of
these animals resemble that of the horse in many respects, much more
indeed than any other existing species, but, instead of the single toe on each
foot, so characteristic of all modern equines, the various species of
Orohippus had four toes before and three behind, all of which reached the
ground. The skull, too, was proportionately shorter, and the orbit was not
enclosed behind by a bridge of bone. There were fifty four teeth in all, and
the premolars were larger than the molars. The crowns of these teeth were
very short. The canine teeth were developed in both sexes, and the incisors
did not have the "mark" which indicates the age of the modern horse. The
radius and ulna were separate, and the latter was entire through the whole
length. The tibia and fibula were distinct. In the forefoot all the digits
except the pollex, or first, were well developed. The third digit is the
largest, and its close resemblance to that of the horse is clearly marked. The
terminal phalanx, or coffin-bone, has a shallow median bone in front, as in
many species of this group in the later tertiary. The fourth digit exceeds the
second in size, and the second is much the shortest of all. Its metacarpal
bone is considerably curved outward. In the hind-foot of this genus there
are but three digits. The fourth metatarsal is much larger than the second.
"The larger number of equine mammals now known from the tertiary
deposits of this country, and their regular distributions through the
subdivisions of this formation, afford a good opportunity to ascertain the
probable descent of the modern horse. The American representative of the
latter is the extinct Equus fraternus (Leidy), a species almost, if not wholly,
identical with the Old World Equus caballus (Linnaeus), to which our recent
horse belongs. Huxley has traced successfully the later genealogy of the
horse through European extinct forms, but the line in America was probably

a more direct one, and the record is more complete. Taking, then, as the
extreme of a series, Orohippus agilis (Marsh), from the eocene, and Equus
fraternus (Leidy), from the quaternary, intermediate forms may be
intercalated with considerable certainty from thirty or more well-marked
species that lived in the intervening periods. The natural line of descent
would seem to be through the following genera: Orohippus, of the eocene;
Miohippus and Anchitherium, of the miocene; Anchippus, Hipparion,
Protohippus, Phohippus, of the pliocene; and Equus, quaternary and recent.
"The most marked changes undergone by the successive equine genera
are as follows: First, increase in size; second, increase in speed, through
concentration of limb bones; third, elongation of head and neck, and
modifications of skull. The eocene Orohippus was the size of a fox.
Miohippus and Anchitherium, from the miocene, were about as large as a
sheep. Hipparion and Pliohippus, of the pliocene, equalled the ass in height;
while the size of the quaternary Equus was fully up to that of a modern
horse.
"The increase of speed was equally well marked, and was a direct result
of the gradual formation of the limbs. The latter were slowly concentrated
by the reduction of their lateral elements and enlargement of the axial bone,
until the force exerted by each limb came to act directly through its axis in
the line of motion. This concentration is well seen—e.g., in the fore-limb.
There was, first, a change in the scapula and humerus, especially in the
latter, which facilitated motion in one line only; second, an expansion of the
radius and reduction of the ulna, until the former alone remained entire and
effective; third, a shortening of all the carpal bones and enlargement of the
median ones, insuring a firmer wrist; fourth, an increase of size of the third
digit, at the expense of those of each side, until the former alone supported
the limb.
"Such is, in brief, a general outline of the more marked changes that
seemed to have produced in America the highly specialized modern Equus
from his diminutive four-toed predecessor, the eocene Orohippus. The line
of descent appears to have been direct, and the remains now known supply
every important intermediate form. It is, of course, impossible to say with
certainty through which of the three-toed genera of the pliocene that lived
together the succession came. It is not impossible that the latter species,
which appear generically identical, are the descendants of more distinct

pliocene types, as the persistent tendency in all the earlier forms was in the
same direction. Considering the remarkable development of the group
through the tertiary period, and its existence even later, it seems very
strange that none of the species should have survived, and that we are
indebted for our present horse to the Old World."(7)
PALEONTOLOGY OF EVOLUTION
These and such-like revelations have come to light in our own time—are,
indeed, still being disclosed. Needless to say, no index of any sort now
attempts to conceal them; yet something has been accomplished towards the
same end by the publication of the discoveries in Smithsonian bulletins and
in technical memoirs of government surveys. Fortunately, however, the
results have been rescued from that partial oblivion by such interpreters as
Professors Huxley and Cope, so the unscientific public has been allowed to
gain at least an inkling of the wonderful progress of paleontology in our
generation.
The writings of Huxley in particular epitomize the record. In 1862 he
admitted candidly that the paleontological record as then known, so far as it
bears on the doctrine of progressive development, negatives that doctrine.
In 1870 he was able to "soften somewhat the Brutus-like severity" of his
former verdict, and to assert that the results of recent researches seem "to
leave a clear balance in favor of the doctrine of the evolution of living
forms one from another." Six years later, when reviewing the work of
Marsh in America and of Gaudry in Pikermi, he declared that, "on the
evidence of paleontology, the evolution of many existing forms of animal
life from their predecessors is no longer an hypothesis, but an historical
fact." In 1881 he asserted that the evidence gathered in the previous decade
had been so unequivocal that, had the transmutation hypothesis not existed,
"the paleontologist would have had to invent it."
Since then the delvers after fossils have piled proof on proof in
bewildering profusion. The fossil-beds in the "bad lands" of western
America seem inexhaustible. And in the Connecticut River Valley near
relatives of the great reptiles which Professor Marsh and others have found
in such profusion in the West left their tracks on the mud-flats—since
turned to sandstone; and a few skeletons also have been found. The bodies
of a race of great reptiles that were the lords of creation of their day have
been dissipated to their elements, while the chance indentations of their feet

as they raced along the shores, mere footprints on the sands, have been
preserved among the most imperishable of the memory-tablets of the world.
Of the other vertebrate fossils that have been found in the eastern
portions of America, among the most abundant and interesting are the
skeletons of mastodons. Of these one of the largest and most complete is
that which was unearthed in the bed of a drained lake near Newburg, New
York, in 1845. This specimen was larger than the existing elephants, and
had tusks eleven feet in length. It was mounted and described by Dr. John
C. Warren, of Boston, and has been famous for half a century as the
"Warren mastodon."
But to the student of racial development as recorded by the fossils all
these sporadic finds have but incidental interest as compared with the rich
Western fossil-beds to which we have already referred. From records here
unearthed, the racial evolution of many mammals has in the past few years
been made out in greater or less detail. Professor Cope has traced the
ancestry of the camels (which, like the rhinoceroses, hippopotami, and
sundry other forms now spoken of as "Old World," seem to have had their
origin here) with much completeness.
A lemuroid form of mammal, believed to be of the type from which man
has descended, has also been found in these beds. It is thought that the
descendants of this creature, and of the other "Old-World" forms above
referred to, found their way to Asia, probably, as suggested by Professor
Marsh, across a bridge at Bering Strait, to continue their evolution on the
other hemisphere, becoming extinct in the land of their nativity. The ape-
man fossil found in the tertiary strata of the island of Java in 1891 by the
Dutch surgeon Dr. Eugene Dubois, and named Pithecanthropus erectus,
may have been a direct descendant of the American tribe of primitive
lemurs, though this is only a conjecture.
Not all the strange beasts which have left their remains in our "bad lands"
are represented by living descendants. The titanotheres, or brontotheridae,
for example, a gigantic tribe, offshoots of the same stock which produced
the horse and rhinoceros, represented the culmination of a line of descent.
They developed rapidly in a geological sense, and flourished about the
middle of the tertiary period; then, to use Agassiz's phrase," time fought
against them." The story of their evolution has been worked out by
Professors Leidy, Marsh, Cope, and H. F. Osborne.

A recent bit of paleontological evidence bearing on the question of the
introduction of species is that presented by Dr. J. L. Wortman in connection
with the fossil lineage of the edentates. It was suggested by Marsh, in 1877,
that these creatures, whose modern representatives are all South American,
originated in North America long before the two continents had any land
connection. The stages of degeneration by which these animals gradually
lost the enamel from their teeth, coming finally to the unique condition of
their modern descendants of the sloth tribe, are illustrated by strikingly
graded specimens now preserved in the American Museum of Natural
History, as shown by Dr. Wortman.
All these and a multitude of other recent observations that cannot be even
outlined here tell the same story. With one accord paleontologists of our
time regard the question of the introduction of new species as solved. As
Professor Marsh has said, "to doubt evolution today is to doubt science; and
science is only another name for truth."
Thus the third great battle over the meaning of the fossil records has
come to a conclusion. Again there is a truce to controversy, and it may seem
to the casual observer that the present stand of the science of fossils is final
and impregnable. But does this really mean that a full synopsis of the story
of paleontology has been told? Or do we only await the coming of the
twentieth-century Lamarck or Darwin, who shall attack the fortified
knowledge of to-day with the batteries of a new generalization?

IV. THE ORIGIN AND DEVELOPMENT OF
MODERN GEOLOGY
JAMES HUTTON
One might naturally suppose that the science of the earth which lies at
man's feet would at least have kept pace with the science of the distant stars.
But perhaps the very obviousness of the phenomena delayed the study of
the crust of the earth. It is the unattainable that allures and mystifies and
enchants the developing mind. The proverbial child spurns its toys and cries
for the moon.
So in those closing days of the eighteenth century, when astronomers had
gone so far towards explaining the mysteries of the distant portions of the
universe, we find a chaos of opinion regarding the structure and formation
of the earth. Guesses were not wanting to explain the formation of the
world, it is true, but, with one or two exceptions, these are bizarre indeed.
One theory supposed the earth to have been at first a solid mass of ice,
which became animated only after a comet had dashed against it. Other
theories conceived the original globe as a mass of water, over which floated
vapors containing the solid elements, which in due time were precipitated
as a crust upon the waters. In a word, the various schemes supposed the
original mass to have been ice, or water, or a conglomerate of water and
solids, according to the random fancies of the theorists; and the final
separation into land and water was conceived to have taken place in all the
ways which fancy, quite unchecked by any tenable data, could invent.
Whatever important changes in the general character of the surface of the
globe were conceived to have taken place since its creation were generally
associated with the Mosaic: deluge, and the theories which attempted to
explain this catastrophe were quite on a par with those which dealt with a
remoter period of the earth's history. Some speculators, holding that the
interior of the globe is a great abyss of waters, conceived that the crust had
dropped into this chasm and had thus been inundated. Others held that the
earth had originally revolved on a vertical axis, and that the sudden change
to its present position bad caused the catastrophic shifting of its oceans. But

perhaps the favorite theory was that which supposed a comet to have
wandered near the earth, and in whirling about it to have carried the waters,
through gravitation, in a vast tide over the continents.
Thus blindly groped the majority of eighteenth-century philosophers in
their attempts to study what we now term geology. Deluded by the old
deductive methods, they founded not a science, but the ghost of a science,
as immaterial and as unlike anything in nature as any other phantom that
could be conjured from the depths of the speculative imagination. And all
the while the beckoning earth lay beneath the feet of these visionaries; but
their eyes were fixed in air.
At last, however, there came a man who had the penetration to see that
the phantom science of geology needed before all else a body corporeal,
and who took to himself the task of supplying it. This was Dr. James
Hutton, of Edinburgh, physician, farmer, and manufacturing chemist—
patient, enthusiastic, level-headed devotee of science. Inspired by his love
of chemistry to study the character of rocks and soils, Hutton had not gone
far before the earth stood revealed to him in a new light. He saw, what
generations of predecessors had blindly refused to see, that the face of
nature everywhere, instead of being rigid and immutable, is perennially
plastic, and year by year is undergoing metamorphic changes. The solidest
rocks are day by day disintegrated slowly, but none the less surely, by wind
and rain and frost, by mechanical attrition and chemical decomposition, to
form the pulverized earth and clay. This soil is being swept away by
perennial showers, and carried off to the oceans. The oceans themselves
beat on their shores, and eat insidiously into the structure of sands and
rocks. Everywhere, slowly but surely, the surface of the land is being worn
away; its substance is being carried to burial in the seas.
Should this denudation continue long enough, thinks Hutton, the entire
surface of the continents must be worn away. Should it be continued LONG
ENOUGH! And with that thought there flashes on his mind an inspiring
conception—the idea that solar time is long, indefinitely long. That seems a
simple enough thought—almost a truism—to the twentieth-century mind;
but it required genius to conceive it in the eighteenth. Hutton pondered it,
grasped its full import, and made it the basis of his hypothesis, his "theory
of the earth."
MODERN GEOLOGY

The hypothesis is this—that the observed changes of the surface of the
earth, continued through indefinite lapses of time, must result in conveying
all the land at last to the sea; in wearing continents away till the oceans
overflow them. What then? Why, as the continents wear down, the oceans
are filling up. Along their bottoms the detritus of wasted continents is
deposited in strata, together with the bodies of marine animals and
vegetables. Why might not this debris solidify to form layers of rocks—the
basis of new continents? Why not, indeed?
But have we any proof that such formation of rocks in an ocean-bed has,
in fact, occurred? To be sure we have. It is furnished by every bed of
limestone, every outcropping fragment of fossil-bearing rock, every
stratified cliff. How else than through such formation in an ocean-bed came
these rocks to be stratified? How else came they to contain the shells of
once living organisms imbedded in their depths? The ancients, finding
fossil shells imbedded in the rocks, explained them as mere freaks of
"nature and the stars." Less superstitious generations had repudiated this
explanation, but had failed to give a tenable solution of the mystery. To
Hutton it is a mystery no longer. To him it seems clear that the basis of the
present continents was laid in ancient sea-beds, formed of the detritus of
continents yet more ancient.
But two links are still wanting to complete the chain of Hutton's
hypothesis. Through what agency has the ooze of the ocean-bed been
transformed into solid rock? and through what agency has this rock been
lifted above the surface of the water to form new continents? Hutton looks
about him for a clew, and soon he finds it. Everywhere about us there are
outcropping rocks that are not stratified, but which give evidence to the
observant eye of having once been in a molten state. Different minerals are
mixed together; pebbles are scattered through masses of rock like plums in
a pudding; irregular crevices in otherwise solid masses of rock—so-called
veinings—are seen to be filled with equally solid granite of a different
variety, which can have gotten there in no conceivable way, so Hutton
thinks, but by running in while molten, as liquid metal is run into the
moulds of the founder. Even the stratified rocks, though they seemingly
have not been melted, give evidence in some instances of having been
subjected to the action of heat. Marble, for example, is clearly nothing but
calcined limestone.

With such evidence before him, Hutton is at no loss to complete his
hypothesis. The agency which has solidified the ocean-beds, he says, is
subterranean heat. The same agency, acting excessively, has produced
volcanic cataclysms, upheaving ocean-beds to form continents. The rugged
and uneven surfaces of mountains, the tilted and broken character of
stratified rocks everywhere, are the standing witnesses of these gigantic
upheavals.
And with this the imagined cycle is complete. The continents, worn away
and carried to the sea by the action of the elements, have been made over
into rocks again in the ocean-beds, and then raised once more into
continents. And this massive cycle, In Hutton's scheme, is supposed to have
occurred not once only, but over and over again, times without number. In
this unique view ours is indeed a world without beginning and without end;
its continents have been making and unmaking in endless series since time
began.
Hutton formulated his hypothesis while yet a young man, not long after
the middle of the century. He first gave it publicity in 1781, in a paper
before the Royal Society of Edinburgh:
"A solid body of land could not have answered the purpose of a habitable
world," said Hutton, "for a soil is necessary to the growth of plants, and a
soil is nothing but the material collected from the destruction of the solid
land. Therefore the surface of this land inhabited by man, and covered by
plants and animals, is made by nature to decay, in dissolving from that hard
and compact state in which it is found; and this soil is necessarily washed
away by the continual circulation of the water running from the summits of
the mountains towards the general receptacle of that fluid.
"The heights of our land are thus levelled with our shores, our fertile
plains are formed from the ruins of the mountains; and those travelling
materials are still pursued by the moving water, and propelled along the
inclined surface of the earth. These movable materials, delivered into the
sea, cannot, for a long continuance, rest upon the shore, for by the agitation
of the winds, the tides, and the currents every movable thing is carried
farther and farther along the shelving bottom of the sea, towards the
unfathomable regions of the ocean.
"If the vegetable soil is thus constantly removed from the surface of the
land, and if its place is then to be supplied from the dissolution of the solid

earth as here represented, we may perceive an end to this beautiful machine;
an end arising from no error in its constitution as a world, but from that
destructibility of its land which is so necessary in the system of the globe, in
the economy of life and vegetation.
"The immense time necessarily required for the total destruction of the
land must not be opposed to that view of future events which is indicated by
the surest facts and most approved principles. Time, which measures
everything in our idea, and is often deficient to our schemes, is to nature
endless and as nothing; it cannot limit that by which alone it has existence;
and as the natural course of time, which to us seems infinite, cannot be
bounded by any operation that may have an end, the progress of things
upon this globe that in the course of nature cannot be limited by time must
proceed in a continual succession. We are, therefore, to consider as
inevitable the destruction of our land, so far as effected by those operations
which are necessary in the purpose of the globe, considered as a habitable
world, and so far as we have not examined any other part of the economy of
nature, in which other operations and a different intention might appear.
"We have now considered the globe of this earth as a machine,
constructed upon chemical as well as mechanical principles, by which its
different parts are all adapted, in form, in quality, and quantity, to a certain
end—an end attained with certainty of success, and an end from which we
may perceive wisdom in contemplating the means employed.
"But is this world to be considered thus merely as a machine, to last no
longer than its parts retain their present position, their proper forms and
qualities? Or may it not be also considered as an organized body such as has
a constitution, in which the necessary decay of the machine is naturally
repaired in the exertion of those productive powers by which it has been
formed?
"This is the view in which we are now to examine the globe; to see if
there be, in the constitution of the world, a reproductive operation by which
a ruined constitution may be again repaired and a duration of stability thus
procured to the machine considered as a world containing plants and
animals.
"If no such reproductive power, or reforming operation, after due inquiry,
is to be found in the constitution of this world, we should have reason to

conclude that the system of this earth has either been intentionally made
imperfect or has not been the work of infinite power and wisdom."(1)
This, then, was the important question to be answered—the question of
the constitution of the globe. To accomplish this, it was necessary, first of
all, to examine without prejudice the material already in hand, adding such
new discoveries from time to time as might be made, but always applying
to the whole unvarying scientific principles and inductive methods of
reasoning.
"If we are to take the written history of man for the rule by which we
should judge of the time when the species first began," said Hutton, "that
period would be but little removed from the present state of things. The
Mosaic history places this beginning of man at no great distance; and there
has not been found, in natural history, any document by which high
antiquity might be attributed to the human race. But this is not the case with
regard to the inferior species of animals, particularly those which inhabit
the ocean and its shores. We find in natural history monuments which prove
that those animals had long existed; and we thus procure a measure for the
computation of a period of time extremely remote, though far from being
precisely ascertained.
"In examining things present, we have data from which to reason with
regard to what has been; and from what actually has been we have data for
concluding with regard to that which is to happen hereafter. Therefore, upon
the supposition that the operations of nature are equable and steady, we
find, in natural appearances, means for concluding a certain portion of time
to have necessarily elapsed in the production of those events of which we
see the effects.
"It is thus that, in finding the relics of sea animals of every kind in the
solid body of our earth, a natural history of those animals is formed, which
includes a certain portion of time; and for the ascertaining this portion of
time we must again have recourse to the regular operations of this world.
We shall thus arrive at facts which indicate a period to which no other
species of chronology is able to remount.
"We find the marks of marine animals in the most solid parts of the earth,
consequently those solid parts have been formed after the ocean was
inhabited by those animals which are proper to that fluid medium. If,
therefore, we knew the natural history of these solid parts, and could trace

the operations of the globe by which they have been formed, we would
have some means for computing the time through which those species of
animals have continued to live. But how shall we describe a process which
nobody has seen performed and of which no written history gives any
account? This is only to be investigated, first, in examining the nature of
those solid bodies the history of which we want to know; and, secondly, in
examining the natural operations of the globe, in order to see if there now
exist such operations as, from the nature of the solid bodies, appear to have
been necessary for their formation.
"There are few beds of marble or limestone in which may not be found
some of those objects which indicate the marine object of the mass. If, for
example, in a mass of marble taken from a quarry upon the top of the Alps
or Andes there shall be found one cockle-shell or piece of coral, it must be
concluded that this bed of stone has been originally formed at the bottom of
the sea, as much as another bed which is evidently composed almost
altogether of cockle-shells and coral. If one bed of limestone is thus found
to have been of marine origin, every concomitant bed of the same kind must
be also concluded to have been formed in the same manner.
"In those calcareous strata, which are evidently of marine origin, there
are many parts which are of sparry structure—that is to say, the original
texture of those beds in such places has been dissolved, and a new structure
has been assumed which is peculiar to a certain state of the calcareous
earth. This change is produced by crystallization, in consequence of a
previous state of fluidity, which has so disposed the concerting parts as to
allow them to assume a regular shape and structure proper to that substance.
A body whose external form has been modified by this process is called a
CRYSTAL; one whose internal arrangement of parts is determined by it is
said to be of a SPARRY STRUCTURE, and this is known from its fracture.
"There are, in all the regions of the earth, huge masses of calcareous
matter in that crystalline form or sparry state in which, perhaps, no vestige
can be found of any organized body, nor any indication that such calcareous
matter has belonged to animals; but as in other masses this sparry structure
or crystalline state is evidently assumed by the marine calcareous
substances in operations which are natural to the globe, and which are
necessary to the consolidation of the strata, it does not appear that the
sparry masses in which no figured body is formed have been originally

different from other masses, which, being only crystallized in part, and in
part still retaining their original form, have ample evidence of their marine
origin.
"We are led, in this manner, to conclude that all the strata of the earth, not
only those consisting of such calcareous masses, but others superincumbent
upon these, have had their origin at the bottom of the sea.
"The general amount of our reasoning is this, that nine-tenths, perhaps, or
ninety-nine-hundredths, of this earth, so far as we see, have been formed by
natural operations of the globe in collecting loose materials and depositing
them at the bottom of the sea; consolidating those collections in various
degrees, and either elevating those consolidated masses above the level on
which they were formed or lowering the level of that sea.
"Let us now consider how far the other proposition of strata being
elevated by the power of heat above the level of the sea may be confirmed
from the examination of natural appearances. The strata formed at the
bottom of the ocean are necessarily horizontal in their position, or nearly so,
and continuous in their horizontal direction or extent. They may be changed
and gradually assume the nature of each other, so far as concerns the
materials of which they are formed, but there cannot be any sudden change,
fracture, or displacement naturally in the body of a stratum. But if the strata
are cemented by the heat of fusion, and erected with an expansive power
acting below, we may expect to find every species of fracture, dislocation,
and contortion in those bodies and every degree of departure from a
horizontal towards a vertical position.
"The strata of the globe are actually found in every possible position: for
from horizontal they are frequently found vertical; from continuous they are
broken and separated in every possible direction; and from a plane they are
bent and doubled. It is impossible that they could have originally been
formed, by the known laws of nature, in their present state and position; and
the power that has been necessarily required for their change has not been
inferior to that which might have been required for their elevation from the
place in which they have been formed."(2)
From all this, therefore, Hutton reached the conclusion that the elevation
of the bodies of land above the water on the earth's surface had been
effected by the same force which had acted in consolidating the strata and

giving them stability. This force he conceived to be exerted by the
expansion of heated matter.
"We have," he said, "been now supposing that the beginning of our
present earth had been laid in the bottom of the ocean, at the completion of
the former land, but this was only for the sake of distinctness. The just view
is this, that when the former land of the globe had been complete, so as to
begin to waste and be impaired by the encroachment of the sea, the present
land began to appear above the surface of the ocean. In this manner we
suppose a due proportion to be always preserved of land and water upon the
surface of the globe, for the purpose of a habitable world such as this which
we possess. We thus also allow time and opportunity for the translation of
animals and plants to occupy the earth.
"But if the earth on which we live began to appear in the ocean at the
time when the LAST began to be resolved, it could not be from the
materials of the continent immediately preceding this which we examine
that the present earth has been constructed; for the bottom of the ocean must
have been filled with materials before land could be made to appear above
its surface.
"Let us suppose that the continent which is to succeed our land is at
present beginning to appear above the water in the middle of the Pacific
Ocean; it must be evident that the materials of this great body, which is
formed and ready to be brought forth, must have been collected from the
destruction of an earth which does not now appear. Consequently, in this
true statement of the case there is necessarily required the destruction of an
animal and vegetable earth prior to the former land; and the materials of
that earth which is first in our account must have been collected at the
bottom of the ocean, and begun to be concocted for the production of the
present earth, when the land immediately preceding the present had arrived
at its full extent.
"We have now got to the end of our reasoning; we have no data further to
conclude immediately from that which actually is; but we have got enough;
we have the satisfaction to find that in nature there are wisdom, system, and
consistency. For having in the natural history of the earth seen a succession
of worlds, we may from this conclude that there is a system in nature; in
like manner as, from seeing revolutions of the planets, it is concluded that
there is a system by which they are intended to continue those revolutions.

But if the succession of worlds is established in the system of nature, it is in
vain to look for anything higher in the origin of the earth. The result,
therefore, of our present inquiry is that we find no vestige of a beginning—
no prospect of an end."
Altogether remarkable as this paper seems in the light of later
knowledge, neither friend nor foe deigned to notice it at the moment. It was
not published in book form until the last decade of the century, when
Hutton had lived with and worked over his theory for almost fifty years.
Then it caught the eye of the world. A school of followers expounded the
Huttonian doctrines; a rival school under Werner in Germany opposed some
details of the hypothesis, and the educated world as a whole viewed the
disputants askance. The very novelty of the new views forbade their
immediate acceptance. Bitter attacks were made upon the "heresies," and
that was meant to be a soberly tempered judgment which in 1800
pronounced Hutton's theories "not only hostile to sacred history, but equally
hostile to the principles of probability, to the results of the ablest
observations on the mineral kingdom, and to the dictates of rational
philosophy." And all this because Hutton's theory presupposed the earth to
have been in existence more than six thousand years.
Thus it appears that though the thoughts of men had widened, in those
closing days of the eighteenth century, to include the stars, they had not as
yet expanded to receive the most patent records that are written everywhere
on the surface of the earth. Before Hutton's views could be accepted, his
pivotal conception that time is long must be established by convincing
proofs. The evidence was being gathered by William Smith, Cuvier, and
other devotees of the budding science of paleontology in the last days of the
century, but their labors were not brought to completion till a subsequent
epoch.
NEPTUNISTS VERSUS PLUTONISTS
In the mean time, James Hutton's theory that continents wear away and
are replaced by volcanic upheaval gained comparatively few adherents.
Even the lucid Illustrations of the Huttonian Theory, which Playfair, the
pupil and friend of the great Scotchman, published in 1802, did not at once
prove convincing. The world had become enamoured of the rival theory of
Hutton's famous contemporary, Werner of Saxony—the theory which taught
that "in the beginning" all the solids of the earth's present crust were

dissolved in the heated waters of a universal sea. Werner affirmed that all
rocks, of whatever character, had been formed by precipitation from this sea
as the waters cooled; that even veins have originated in this way; and that
mountains are gigantic crystals, not upheaved masses. In a word, he
practically ignored volcanic action, and denied in toto the theory of
metamorphosis of rocks through the agency of heat.
The followers of Werner came to be known as Neptunists; the Huttonians
as Plutonists. The history of geology during the first quarter of the
nineteenth century is mainly a recital of the intemperate controversy
between these opposing schools; though it should not be forgotten that,
meantime, the members of the Geological Society of London were making
an effort to hunt for facts and avoid compromising theories. Fact and theory,
however, were too closely linked to be thus divorced.
The brunt of the controversy settled about the unstratified rocks—
granites and their allies—which the Plutonists claimed as of igneous origin.
This contention had the theoretical support of the nebular hypothesis, then
gaining ground, which supposed the earth to be a cooling globe. The
Plutonists laid great stress, too, on the observed fact that the temperature of
the earth increases at a pretty constant ratio as descent towards its centre is
made in mines. But in particular they appealed to the phenomena of
volcanoes.
The evidence from this source was gathered and elaborated by Mr. G.
Poulett Scrope, secretary of the Geological Society of England, who, in
1823, published a classical work on volcanoes in which he claimed that
volcanic mountains, including some of the highest-known peaks, are merely
accumulated masses of lava belched forth from a crevice in the earth's crust.
"Supposing the globe to have had any irregular shape when detached
from the sun," said Scrope, "the vaporization of its surface, and, of course,
of its projecting angles, together with its rotatory motion on its axis and the
liquefaction of its outer envelope, would necessarily occasion its actual
figure of an oblate spheroid. As the process of expansion proceeded in
depth, the original granitic beds were first partially disaggregated, next
disintegrated, and more or less liquefied, the crystals being merged in the
elastic vehicle produced by the vaporization of the water contained between
the laminae.

"Where this fluid was produced in abundance by great dilatation—that is,
in the outer and highly disintegrated strata, the superior specific gravity of
the crystals forced it to ooze upward, and thus a great quantity of aqueous
vapor was produced on the surface of the globe. As this elastic fluid rose
into outer space, its continually increasing expansion must have
proportionately lowered its temperature; and, in consequence, a part was
recondensed into water and sank back towards the more solid surface of the
globe.
"And in this manner, for a certain time, a violent reciprocation of
atmospheric phenomena must have continued—torrents of vapor rising
outwardly, while equally tremendous torrents of condensed vapor, or rain,
fell towards the earth. The accumulation of the latter on the yet unstable and
unconsolidated surface of the globe constituted the primeval ocean. The
surface of this ocean was exposed to continued vaporization owing to
intense heat; but this process, abstracting caloric from the stratum of the
water below, by partially cooling it, tended to preserve the remainder in a
liquid form. The ocean will have contained, both in solution and
suspension, many of the matters carried upward from the granitic bed in
which the vapors from whose condensation it proceeded were produced,
and which they had traversed in their rise. The dissolved matters will have
been silex, carbonates, and sulphates of lime, and those other mineral
substances which water at an intense temperature and under such
circumstances was enabled to hold in solution. The suspended substances
will have been all the lighter and finer particles of the upper beds where the
disintegration had been extreme; and particularly their mica, which, owing
to the tenuity of its plate-shaped crystals, would be most readily carried up
by the ascending fluid, and will have remained longest in suspension.
"But as the torrents of vapor, holding these various matters in solution
and suspension, were forced upward, the greater part of the disintegrated
crystals by degrees subsided; those of felspar and quartz first, the mica
being, as observed above, from the form of its plates, of peculiar buoyancy,
and therefore held longest in suspension.
"The crystals of felspar and quartz as they subsided, together with a small
proportion of mica, would naturally arrange themselves so as to have their
longest dimensions more or less parallel to the surface on which they rest;
and this parallelism would be subsequently increased, as we shall see

hereafter, by the pressure of these beds sustained between the weight of the
supported column of matter and the expansive force beneath them. These
beds I conceive, when consolidated, to constitute the gneiss formation.
"The farther the process of expansion proceeded in depth, the more was
the column of liquid matter lengthened, which, gravitating towards the
centre of the globe, tended to check any further expansion. It is, therefore,
obvious that after the globe settled into its actual orbit, and thenceforward
lost little of its enveloping matter, the whole of which began from that
moment to gravitate towards its centre, the progress of expansion inwardly
would continually increase in rapidity; and a moment must have at length
arrived hen the forces of expansion and repression had reached an
equilibrium and the process was stopped from progressing farther inwardly
by the great pressure of the gravitating column of liquid.
"This column may be considered as consisting of different strata, though
the passage from one extremity of complete solidity to the other of
complete expansion, in reality, must have been perfectly gradual. The
lowest stratum, immediately above the extreme limit of expansion, will
have been granite barely DISAGGREGATED, and rendered imperfectly
liquid by the partial vaporization of its contained water.
"The second stratum was granite DISINTEGRATED; aqueous vapor,
having been produced in such abundance as to be enabled to rise upward,
partially disintegrating the crystals of felspar and mica, and superficially
dissolving those of quartz. This mass would reconsolidate into granite,
though of a smaller grain than the preceding rock.
"The third stratum was so disintegrated that a greater part of the mica had
been carried up by the escaping vapor IN SUSPENSION, and that of quartz
in solution; the felspar crystals, with the remaining quartz and mica,
SUBSIDING by their specific gravity and arranging themselves in
horizontal planes.
"The consolidation of this stratum produced the gneiss formation.
"The fourth zone will have been composed of the ocean of turbid and
heated water, holding mica, etc., in suspension, and quartz, carbonate of
lime, etc., in solution, and continually traversed by reciprocating bodies of
heated water rising from below, and of cold fluid sinking from the surface,
by reason of their specific gravities.

"The disturbance thus occasioned will have long retarded the deposition
of the suspended particles. But this must by degrees have taken place, the
quartz grains and the larger and coarser plates of mica subsiding first and
the finest last.
"But the fragments of quartz and mica were not deposited alone; a great
proportion of the quartz held in SOLUTION must have been precipitated at
the same time as the water cooled, and therefore by degrees lost its faculty
of so much in solution. Thus was gradually produced the formation of mica-
schist, the mica imperfectly recrystallizing or being merely aggregated
together in horizontal plates, between which the quartz either spread itself
generally in minute grains or unified into crystalline nuclei. On other spots,
instead of silex, carbonate of lime was precipitated, together with more or
less of the nucaceous sediment, and gave rise to saccharoidal limestones. At
a later period, when the ocean was yet further cooled down, rock-salt and
sulphate of lime were locally precipitated in a similar mode.
"The fifth stratum was aeriform, and consisted in great part of aqueous
vapors; the remainder being a compound of other elastic fluids (permanent
gases) which had been formed probably from the volatilization of some of
the substances contained in the primitive granite and carried upward with
the aqueous vapor from below. These gases will have been either mixed
together or otherwise disposed, according to their different specific gravities
or chemical affinities, and this stratum constituted the atmosphere or aerial
envelope of the globe.
"When, in this manner, the general and positive expansion of the globe,
occasioned by the sudden reduction of outward pressure, had ceased (in
consequence of the REPRESSIVE FORCE, consisting of the weight of its
fluid envelope, having reached an equilibrium with the EXPANSIVE
FORCE, consisting of the caloric of the heated nucleus), the rapid
superficial evaporation of the ocean continued; and, by gradually reducing
its temperature, occasioned the precipitation of a proportionate quantity of
the minerals it held in solution, particularly its silex. These substances
falling to the bottom, accompanied by a large proportion of the matters held
in solution, particularly the mica, in consequence of the greater comparative
tranquillity of the ocean, agglomerated these into more or less compact beds
of rock (the mica-schist formation), producing the first crust or solid
envelope of the globe. Upon this, other stratified rocks, composed

sometimes of a mixture, sometimes of an alternation of precipitations,
sediments, and occasionally of conglomerates, were by degrees deposited,
giving rise to the TRANSITION formations.
"Beneath this crust a new process now commenced. The outer zones of
crystalline matter having been suddenly refrigerated by the rapid
vaporization and partial escape of the water they contained, abstracted
caloric from the intensely heated nucleus of the globe. These crystalline
zones were of unequal density, the expansion they had suffered diminishing
from above downward.
"Their expansive force was, however, equal at all points, their
temperature everywhere bearing an inverse ratio to their density. But when
by the accession of caloric from the inner and unliquefied nucleus the
temperature, and consequently the expansive force of the lower strata of
dilated crystalline matter, was augmented, it acted upon the upper and more
liquefied strata. These being prevented from yielding OUTWARDLY by the
tenacity and weight of the solid involucrum of precipitated and sedimental
deposits which overspread them, sustained a pressure out of proportion to
their expansive force, and were in consequence proportionately condensed,
and by the continuance of the process, where the overlying strata were
sufficiently resistant, finally consolidated.
"This process of consolidation must have progressed from above
downward, with the increase of the expansive force in the lower strata,
commencing from the upper surface, which, its temperature being lowest,
offered the least resistance to the force of compression.
"By this process the upper zone of crystalline matter, which had
intumesced so far as to allow of the escape of its aqueous vapor and of
much of its mica and quartz, was resolidified, the component crystals
arranging themselves in planes perpendicular to the direction of the
pressure by which the mass was consolidated—that is, to the radius of the
globe. The gneiss formation, as already observed, was the result.
"The inferior zone of barely disintegrated granite, from which only a part
of the steam and quartz and none of the mica had escaped, reconsolidated in
a confused or granitoidal manner; but exhibits marks of the process it had
undergone in its broken crystals of felspar and mica, its rounded and
superficially dissolved grains of quartz, its imbedded fragments (broken

from the more solid parts of the mass, as it rose, and enveloped by the softer
parts), its concretionary nodules and new minerals, etc.
"Beneath this, the granite which had been simply disintegrated was again
solidified, and returned in all respects to its former condition. The
temperature, however, and with it the expansive force of the inferior zone,
was continually on the increase, the caloric of the interior of the globe still
endeavoring to put itself in equilibrio by passing off towards the less-
intensely heated crust.
"This continually increasing expansive force must at length have
overcome the resistance opposed by the tenacity and weight of the
overlying consolidated strata. It is reasonable to suppose that this result
took place contemporaneously, or nearly so, on many spots, wherever
accidental circumstances in the texture or composition of the oceanic
deposits led them to yield more readily; and in this manner were produced
those original fissures in the primeval crust of the earth through some of
which (fissures of elevation) were intruded portions of interior crystalline
zones in a solid or nearly solid state, together with more or less of the
intumescent granite, in the manner above described; while others (fissures
of eruption) gave rise to extravasations of the heated crystalline matter, in
the form of lavas—that is, still further liquefied by the greater comparative
reduction of the pressure they endured."(3)
The Neptunists stoutly contended for the aqueous origin of volcanic as of
other mountains. But the facts were with Scrope, and as time went on it
came to be admitted that not merely volcanoes, but many "trap" formations
not taking the form of craters, had been made by the obtrusion of molten
rock through fissures in overlying strata. Such, for example, to cite familiar
illustrations, are Mount Holyoke, in Massachusetts, and the well-known
formation of the Palisades along the Hudson.
But to admit the "Plutonic" origin of such widespread formations was
practically to abandon the Neptunian hypothesis. So gradually the
Huttonian explanation of the origin of granites and other "igneous" rocks,
whether massed or in veins, came to be accepted. Most geologists then
came to think of the earth as a molten mass, on which the crust rests as a
mere film. Some, indeed, with Lyell, preferred to believe that the molten
areas exist only as lakes in a solid crust, heated to melting, perhaps, by
electrical or chemical action, as Davy suggested. More recently a popular

theory attempts to reconcile geological facts with the claim of the
physicists, that the earth's entire mass is at least as rigid as steel, by
supposing that a molten film rests between the observed solid crust and the
alleged solid nucleus. But be that as it may, the theory that subterranean
heat has been instrumental in determining the condition of "primary" rocks,
and in producing many other phenomena of the earth's crust, has never been
in dispute since the long controversy between the Neptunists and the
Plutonists led to its establishment.
LYELL AND UNIFORMITARIANISM
If molten matter exists beneath the crust of the earth, it must contract in
cooling, and in so doing it must disturb the level of the portion of the crust
already solidified. So a plausible explanation of the upheaval of continents
and mountains was supplied by the Plutonian theory, as Hutton had from
the first alleged. But now an important difference of opinion arose as to the
exact rationale of such upheavals. Hutton himself, and practically every one
else who accepted his theory, had supposed that there are long periods of
relative repose, during which the level of the crust is undisturbed, followed
by short periods of active stress, when continents are thrown up with
volcanic suddenness, as by the throes of a gigantic earthquake. But now
came Charles Lyell with his famous extension of the "uniformitarian"
doctrine, claiming that past changes of the earth's surface have been like
present changes in degree as well as in kind. The making of continents and
mountains, he said, is going on as rapidly to-day as at any time in the past.
There have been no gigantic cataclysmic upheavals at any time, but all
changes in level of the strata as a whole have been gradual, by slow
oscillation, or at most by repeated earthquake shocks such as are still often
experienced.
In support of this very startling contention Lyell gathered a mass of
evidence of the recent changes in level of continental areas. He
corroborated by personal inspection the claim which had been made by
Playfair in 1802, and by Von Buch in 1807, that the coast-line of Sweden is
rising at the rate of from a few inches to several feet in a century. He cited
Darwin's observations going to prove that Patagonia is similarly rising, and
Pingel's claim that Greenland is slowly sinking. Proof as to sudden changes
of level of several feet, over large areas, due to earthquakes, was brought
forward in abundance. Cumulative evidence left it no longer open to

question that such oscillatory changes of level, either upward or downward,
are quite the rule, and it could not be denied that these observed changes, if
continued long enough in one direction, would produce the highest
elevations. The possibility that the making of even the highest ranges of
mountains had been accomplished without exaggerated catastrophic action
came to be freely admitted.
It became clear that the supposedly stable-land surfaces are in reality
much more variable than the surface of the "shifting sea"; that continental
masses, seemingly so fixed, are really rising and falling in billows
thousands of feet in height, ages instead of moments being consumed in the
sweep between crest and hollow.
These slow oscillations of land surfaces being understood, many
geological enigmas were made clear—such as the alternation of marine and
fresh-water formations in a vertical series, which Cuvier and Brongniart had
observed near Paris; or the sandwiching of layers of coal, of subaerial
formation, between layers of subaqueous clay or sandstone, which may be
observed everywhere in the coal measures. In particular, the extreme
thickness of the sedimentary strata as a whole, many times exceeding the
depth of the deepest known sea, was for the first time explicable when it
was understood that such strata had formed in slowly sinking ocean-beds.
All doubt as to the mode of origin of stratified rocks being thus removed,
the way was opened for a more favorable consideration of that other
Huttonian doctrine of the extremely slow denudation of land surfaces. The
enormous amount of land erosion will be patent to any one who uses his
eyes intelligently in a mountain district. It will be evident in any region
where the strata are tilted—as, for example, the Alleghanies—that great
folds of strata which must once have risen miles in height have in many
cases been worn entirely away, so that now a valley marks the location of
the former eminence. Where the strata are level, as in the case of the
mountains of Sicily, the Scotch Highlands, and the familiar Catskills, the
evidence of denudation is, if possible, even more marked; for here it is clear
that elevation and valley have been carved by the elements out of land that
rose from the sea as level plateaus.
But that this herculean labor of land-sculpturing could have been
accomplished by the slow action of wind and frost and shower was an idea
few men could grasp within the first half-century after Hutton propounded

it; nor did it begin to gain general currency until Lyell's crusade against
catastrophism, begun about 1830, had for a quarter of a century accustomed
geologists to the thought of slow, continuous changes producing final
results of colossal proportions. And even long after that it was combated by
such men as Murchison, Director-General of the Geological Survey of
Great Britain, then accounted the foremost field-geologist of his time, who
continued to believe that the existing valleys owe their main features to
subterranean forces of upheaval. Even Murchison, however, made some
recession from the belief of the Continental authorities, Elie de Beaumont
and Leopold von Buch, who contended that the mountains had sprung up
like veritable jacks-in-the-box. Von Buch, whom his friend and fellow-pupil
Von Humboldt considered the foremost geologist of the time, died in 1853,
still firm in his early faith that the erratic bowlders found high on the Jura
had been hurled there, like cannon-balls, across the valley of Geneva by the
sudden upheaval of a neighboring mountain-range.
AGASSIZ AND THE GLACIAL THEORY
The bowlders whose presence on the crags of the Jura the old Gerinan
accounted for in a manner so theatrical had long been a source of contention
among geologists. They are found not merely on the Jura, but on
numberless other mountains in all north-temperate latitudes, and often far
out in the open country, as many a farmer who has broken his plough
against them might testify. The early geologists accounted for them, as for
nearly everything else, with their supposititious Deluge. Brongniart and
Cuvier and Buckland and their contemporaries appeared to have no
difficulty in conceiving that masses of granite weighing hundreds of tons
had been swept by this current scores or hundreds of miles from their
source. But, of course, the uniformitarian faith permitted no such
explanation, nor could it countenance the projection idea; so Lyell was
bound to find some other means of transportation for the puzzling erratics.
The only available medium was ice, but, fortunately, this one seemed
quite sufficient. Icebergs, said Lyell, are observed to carry all manner of
debris, and deposit it in the sea-bottoms. Present land surfaces have often
been submerged beneath the sea. During the latest of these submergences
icebergs deposited the bowlders now scattered here and there over the land.
Nothing could be simpler or more clearly uniformitarian. And even the
catastrophists, though they met Lyell amicably on almost no other

theoretical ground, were inclined to admit the plausibility of his theory of
erratics. Indeed, of all Lyell's nonconformist doctrines, this seemed the one
most likely to meet with general acceptance.
Yet, even as this iceberg theory loomed large and larger before the
geological world, observations were making in a different field that were
destined to show its fallacy. As early as 1815 a sharp-eyed chamois-hunter
of the Alps, Perraudin by name, had noted the existence of the erratics, and,
unlike most of his companion hunters, had puzzled his head as to how the
bowlders got where he saw them. He knew nothing of submerged
continents or of icebergs, still less of upheaving mountains; and though he
doubtless had heard of the Flood, he had no experience of heavy rocks
floating like corks in water. Moreover, he had never observed stones rolling
uphill and perching themselves on mountain-tops, and he was a good
enough uniformitarian (though he would have been puzzled indeed had any
one told him so) to disbelieve that stones in past times had disported
themselves differently in this regard from stones of the present. Yet there
the stones are. How did they get there?
The mountaineer thought that he could answer that question. He saw
about him those gigantic serpent-like streams of ice called glaciers, "from
their far fountains slow rolling on," carrying with them blocks of granite
and other debris to form moraine deposits. If these glaciers had once been
much more extensive than they now are, they might have carried the
bowlders and left them where we find them. On the other hand, no other
natural agency within the sphere of the chamois-hunter's knowledge could
have accomplished this, ergo the glaciers must once have been more
extensive. Perraudin would probably have said that common-sense drove
him to this conclusion; but be that as it may, he had conceived one of the
few truly original and novel ideas of which the nineteenth century can
boast.
Perraudin announced his idea to the greatest scientist in his little world—
Jean de Charpentier, director of the mines at Bex, a skilled geologist who
had been a fellow-pupil of Von Buch and Von Humboldt under Werner at
the Freiberg School of Mines. Charpentier laughed at the mountaineer's
grotesque idea, and thought no more about it. And ten years elapsed before
Perraudin could find any one who treated his notion with greater respect.
Then he found a listener in M. Venetz, a civil engineer, who read a paper on

the novel glacial theory before a local society in 1823. This brought the
matter once more to the attention of De Charpentier, who now felt that there
might be something in it worth investigation.
A survey of the field in the light of the new theory soon convinced
Charpentier that the chamois-hunter had all along been right. He became an
enthusiastic supporter of the idea that the Alps had once been imbedded in a
mass of ice, and in 1836 he brought the notion to the attention of Louis
Agassiz, who was spending the summer in the Alps. Agassiz was sceptical
at first, but soon became a convert.
In 1840 Agassiz published a paper in which the results of his Alpine
studies were elaborated.
"Let us consider," he says, "those more considerable changes to which
glaciers are subject, or rather, the immense extent which they had in the
prehistoric period. This former immense extension, greater than any that
tradition has preserved, is proved, in the case of nearly every valley in the
Alps, by facts which are both many and well established. The study of these
facts is even easy if the student is looking out for them, and if he will seize
the least indication of their presence; and, if it were a long time before they
were observed and connected with glacial action, it is because the evidences
are often isolated and occur at places more or less removed from the glacier
which originated them. If it be true that it is the prerogative of the scientific
observer to group in the field of his mental vision those facts which appear
to be without connection to the vulgar herd, it is, above all, in such a case as
this that he is called upon to do so. I have often compared these feeble
effects, produced by the glacial action of former ages, with the appearance
of the markings upon a lithographic stone, prepared for the purpose of
preservation, and upon which one cannot see the lines of the draughtsman's
work unless it is known beforehand where and how to search for them.
"The fact of the former existence of glaciers which have now disappeared
is proved by the survival of the various phenomena which always
accompany them, and which continue to exist even after the ice has melted.
These phenomena are as follows:
"1. Moraines.—The disposition and composition of moraines enable
them to be always recognized, even when they are no longer adjacent to a
glacier nor immediately surround its lower extremities. I may remark that
lateral and terminal moraines alone enable us to recognize with certainty the

limits of glacial extension, because they can be easily distinguished from
the dikes and irregularly distributed stones carried down by the Alpine
torrents, The lateral moraines deposited upon the sides of valleys are rarely
affected by the larger torrents, but they are, however, often cut by the small
streams which fall down the side of a mountain, and which, by interfering
with their continuity, make them so much more difficult to recognize.
"2. The Perched Bowlders.—It often happens that glaciers encounter
projecting points of rock, the sides of which become rounded, and around
which funnel-like cavities are formed with more or less profundity. When
glaciers diminish and retire, the blocks which have fallen into these funnels
often remain perched upon the top of the projecting rocky point within it, in
such a state of equilibrium that any idea of a current of water as the cause of
their transportation is completely inadmissible on account of their position.
When such points of rock project above the surface of the glacier or appear
as a more considerable islet in the midst of its mass (such as is the case in
the Jardin of the Mer de Glace, above Montavert), such projections become
surrounded on all sides by stones which ultimately form a sort of crown
around the summit whenever the glaciers decrease or retire completely.
Water currents never produce anything like this; but, on the contrary,
whenever a stream breaks itself against a projecting rock, the stones which
it carries down are turned aside and form a more or less regular trail. Never,
under such circumstances, can the stones remain either at the top or at the
sides of the rock, for, if such a thing were possible, the rapidity of the
current would be accelerated by the increased resistance, and the moving
bowlders would be carried beyond the obstruction before they were finally
deposited.
"3. The polished and striated rocks, such as have been described in
Chapter XIV., afford yet further evidence of the presence of a glacier; for, as
has been said already, neither a current nor the action of waves upon an
extensive beach produces such effects. The general direction of the channels
and furrows indicates the direction of the general movement of the glacier,
and the streaks which vary more or less from this direction are produced by
the local effects of oscillation and retreat, as we shall presently see.
"4. The Lapiaz, or Lapiz, which the inhabitants of German Switzerland
call Karrenfelder, cannot always be distinguished from erosions, because,
both produced as they are by water, they do not differ in their exterior

characteristics, but only in their positions. Erosions due to torrents are
always found in places more or less depressed, and never occur upon large
inclined surfaces. The Lapiaz, on the contrary, are frequently found upon
the projecting parts of the sides of valleys in places where it is not possible
to suppose that water has ever formed a current. Some geologists, in their
embarrassment to explain these phenomena, have supposed that they were
due to the infiltration of acidulated water, but this hypothesis is purely
gratuitous.
"We will now describe the remains of these various phenomena as they
are found in the Alps outside the actual glacial limits, in order to prove that
at a certain epoch glaciers were much larger than they are to-day.
"The ancient moraines, situated as they are at a great distance from those
of the present day, are nowhere so distinct or so frequent as in Valais, where
MM. Venetz and J. de Charpentier noticed them for the first time; but as
their observations are as yet unpublished, and they themselves gave me the
information, it would be an appropriation of their discovery if I were to
describe them here in detail. I will limit myself to say that there can be
found traces, more or less distinct, of ancient terminal moraines in the form
of vaulted dikes at the foot of every glacier, at a distance of a few minutes'
walk, a quarter of an hour, a half-hour, an hour, and even of several leagues
from their present extremities. These traces become less distinct in
proportion to their distance from the glacier, and, since they are also often
traversed by torrents, they are not as continuous as the moraines which are
nearer to the glaciers. The farther these ancient moraines are removed from
the termination of a glacier, the higher up they reach upon the sides of the
valley, which proves to us that the thickness of the glacier must have been
greater when its size was larger. At the same time, their number indicates so
many stopping-places in the retreat of the glacier, or so many extreme limits
of its extension—limits which were never reached again after it had retired.
I insist upon this point, because if it is true that all these moraines
demonstrate a larger extent of the glacier, they also prove that their retreat
into their present boundaries, far from having been catastrophic, was
marked on the contrary by periods of repose more or less frequent, which
caused the formation of a series of concentric moraines which even now
indicate their retrogression.

"The remains of longitudinal moraines are less frequent, less distinct, and
more difficult to investigate, because, indicating as they do the levels to
which the edges of the glacier reached at different epochs, it is generally
necessary to look for them above the line of the paths along the escarpments
of the valleys, and hence it is not always possible to follow them along a
valley. Often, also, the sides of a valley which enclosed a glacier are so
steep that it is only here and there that the stones have remained in place.
They are, nevertheless, very distinct in the lower part of the valley of the
Rhone, between Martigny and the Lake of Geneva, where several parallel
ridges can be observed, one above the other, at a height of one thousand,
one thousand two hundred, and even one thousand five hundred feet above
the Rhone. It is between St. Maurice and the cascade of Pissevache, close to
the hamlet of Chaux-Fleurie, that they are most accessible, for at this place
the sides of the valley at different levels ascend in little terraces, upon
which the moraines have been preserved. They are also very distinct above
the Bains de Lavey, and above the village of Monthey at the entrance of the
Val d'Illiers, where the sides of the valley are less inclined than in many
other places.
"The perched bowlders which are found in the Alpine valleys, at
considerable distances from the glaciers, occupy at times positions so
extraordinary that they excite in a high degree the curiosity of those who
see them. For instance, when one sees an angular stone perched upon the
top of an isolated pyramid, or resting in some way in a very steep locality,
the first inquiry of the mind is, When and how have these stones been
placed in such positions, where the least shock would seem to turn them
over? But this phenomenon is not in the least astonishing when it is seen to
occur also within the limits of actual glaciers, and it is recalled by what
circumstances it is occasioned.
"The most curious examples of perched stones which can be cited are
those which command the northern part of the cascade of Pissevache, close
to Chaux-Fleurie, and those above the Bains de Lavey, close to the village
of Morcles; and those, even more curious, which I have seen in the valley
of St. Nicolas and Oberhasli. At Kirchet, near Meiringen, can be seen some
very remarkable crowns of bowlders around several domes of rock which
appear to have been projected above the surface of the glacier which
surrounded them. Something very similar can be seen around the top of the
rock of St. Triphon.

"The extraordinary phenomenon of perched stones could not escape the
observing eye of De Saussure, who noticed several at Saleve, of which he
described the positions in the following manner: 'One sees,' said he, 'upon
the slope of an inclined meadow, two of these great bowlders of granite,
elevated one upon the other, above the grass at a height of two or three feet,
upon a base of limestone rock on which both rest. This base is a
continuation of the horizontal strata of the mountain, and is even united
with it visibly on its lower face, being cut perpendicularly upon the other
sides, and is not larger than the stone which it supports.' But seeing that the
entire mountain is composed of the same limestone, De Saussure naturally
concluded that it would be absurd to think that it was elevated precisely and
only beneath the blocks of granite. But, on the other hand, since he did not
know the manner in which these perched stones are deposited in our days
by glacial action, he had recourse to another explanation: He supposes that
the rock was worn away around its base by the continual erosion of water
and air, while the portion of the rock which served as the base for the
granite had been protected by it. This explanation, although very ingenious,
could no longer be admitted after the researches of M. Elie de Beaumont
had proved that the action of atmospheric agencies was not by a good deal
so destructive as was theretofore supposed. De Saussure speaks also of a
detached bowlder, situated upon the opposite side of the Tete-Noire, 'which
is,' he says, 'of so great a size that one is tempted to believe that it was
formed in the place it occupies; and it is called Barme russe, because it is
worn away beneath in the form of a cave which can afford accommodation
for more than thirty persons at a time."(4)
But the implications of the theory of glaciers extend, so Agassiz has
come to believe, far beyond the Alps. If the Alps had been covered with an
ice sheet, so had many other regions of the northern hemisphere. Casting
abroad for evidences of glacial action, Agassiz found them everywhere in
the form of transported erratics, scratched and polished outcropping rocks,
and moraine-like deposits. Finally, he became convinced that the ice sheet
that covered the Alps had spread over the whole of the higher latitudes of
the northern hemisphere, forming an ice cap over the globe. Thus the
common-sense induction of the chamois-hunter blossomed in the mind of
Agassiz into the conception of a universal ice age.
In 1837 Agassiz had introduced his theory to the world, in a paper read at
Neuchatel, and three years later he published his famous Etudes sur les

Glaciers, from which we have just quoted. Never did idea make a more
profound disturbance in the scientific world. Von Buch treated it with
alternate ridicule, contempt, and rage; Murchison opposed it with
customary vigor; even Lyell, whose most remarkable mental endowment
was an unfailing receptiveness to new truths, could not at once discard his
iceberg theory in favor of the new claimant. Dr. Buckland, however, after
Agassiz had shown him evidence of former glacial action in his own
Scotland, became a convert—the more readily, perhaps, as it seemed to him
to oppose the uniformitarian idea. Gradually others fell in line, and after the
usual imbittered controversy and the inevitable full generation of probation,
the idea of an ice age took its place among the accepted tenets of geology.
All manner of moot points still demanded attention—the cause of the ice
age, the exact extent of the ice sheet, the precise manner in which it
produced its effects, and the exact nature of these effects; and not all of
these have even yet been determined. But, details aside, the ice age now has
full recognition from geologists as an historical period. There may have
been many ice ages, as Dr. Croll contends; there was surely one; and the
conception of such a period is one of the very few ideas of our century that
no previous century had even so much as faintly adumbrated.
THE GEOLOGICAL AGES
But, for that matter, the entire subject of historical geology is one that had
but the barest beginning before our century. Until the paleontologist found
out the key to the earth's chronology, no one—not even Hutton—could have
any definite idea as to the true story of the earth's past. The only
conspicuous attempt to classify the strata was that made by Werner, who
divided the rocks into three systems, based on their supposed order of
deposition, and called primary, transition, and secondary.
Though Werner's observations were confined to the small province of
Saxony, he did not hesitate to affirm that all over the world the succession
of strata would be found the same as there, the concentric layers, according
to this conception, being arranged about the earth with the regularity of
layers on an onion. But in this Werner was as mistaken as in his theoretical
explanation of the origin of the "primary" rocks. It required but little
observation to show that the exact succession of strata is never precisely the
same in any widely separated regions. Nevertheless, there was a germ of
truth in Werner's system. It contained the idea, however faultily interpreted,

of a chronological succession of strata; and it furnished a working outline
for the observers who were to make out the true story of geological
development. But the correct interpretation of the observed facts could only
be made after the Huttonian view as to the origin of strata had gained
complete acceptance.
When William Smith, having found the true key to this story, attempted
to apply it, the territory with which he had to deal chanced to be one where
the surface rocks are of that later series which Werner termed secondary. He
made numerous subdivisions within this system, based mainly on the
fossils. Meantime it was found that, judged by the fossils, the strata that
Brongniart and Cuvier studied near Paris were of a still more recent period
(presumed at first to be due to the latest deluge), which came to be spoken
of as tertiary. It was in these beds, some of which seemed to have been
formed in fresh-water lakes, that many of the strange mammals which
Cuvier first described were found.
But the "transition" rocks, underlying the "secondary" system that Smith
studied, were still practically unexplored when, along in the thirties, they
were taken in hand by Roderick Impey Murchison, the reformed fox-hunter
and ex-captain, who had turned geologist to such notable advantage, and
Adam Sedgwick, the brilliant Woodwardian professor at Cambridge.
Working together, these two friends classified the
transition rocks into chronological groups, since familiar to every one in
the larger outlines as the Silurian system (age of invertebrates) and the
Devonian system (age of fishes)—names derived respectively from the
country of the ancient Silures, in Wales and Devonshire, England. It was
subsequently discovered that these systems of strata, which crop out from
beneath newer rocks in restricted areas in Britain, are spread out into broad,
undisturbed sheets over thousands of miles in continental Europe and in
America. Later on Murchison studied them in Russia, and described them,
conjointly with Verneuil and Von Kerserling, in a ponderous and classical
work. In America they were studied by Hall, Newberry, Whitney, Dana,
Whitfield, and other pioneer geologists, who all but anticipated their
English contemporaries.
The rocks that are of still older formation than those studied by
Murchison and Sedgwick (corresponding in location to the "primary" rocks
of Werner's conception) are the surface feature of vast areas in Canada, and

were first prominently studied there by William I. Logan, of the Canadian
Government Survey, as early as 1846, and later on by Sir William Dawson.
These rocks—comprising the Laurentian system—were formerly supposed
to represent parts of the original crust of the earth, formed on first cooling
from a molten state; but they are now more generally regarded as once-
stratified deposits metamorphosed by the action of heat.
Whether "primitive" or metamorphic, however, these Canadian rocks,
and analogous ones beneath the fossiliferous strata of other countries, are
the oldest portions of the earth's crust of which geology has any present
knowledge. Mountains of this formation, as the Adirondacks and the Storm
King range, overlooking the Hudson near West Point, are the patriarchs of
their kind, beside which Alleghanies and Sierra Nevadas are recent upstarts,
and Rockies, Alps, and Andes are mere parvenus of yesterday.
The Laurentian rocks were at first spoken of as representing "Azoic"
time; but in 1846 Dawson found a formation deep in their midst which was
believed to b e the fossil relic of a very low form of life, and after that it
became customary to speak of the system as "Eozoic." Still more recently
the title of Dawson's supposed fossil to rank as such has been questioned,
and Dana's suggestion that the early rocks be termed merely Archman has
met with general favor. Murchison and Sedgwick's Silurian, Devonian, and
Carboniferous groups (the ages of invertebrates, of fishes, and of coal
plants, respectively) are together spoken of as representing Paleozoic time.
William Smith's system of strata, next above these, once called "secondary,"
represents Mesozoic time, or the age of reptiles. Still higher, or more recent,
are Cuvier and Brongniart's tertiary rocks, representing the age of
mammals. Lastly, the most recent formations, dating back, however, to a
period far enough from recent in any but a geological sense, are classed as
quaternary, representing the age of man.
It must not be supposed, however, that the successive "ages" of the
geologist are shut off from one another in any such arbitrary way as this
verbal classification might seem to suggest. In point of fact, these "ages"
have no better warrant for existence than have the "centuries" and the
"weeks" of every-day computation. They are convenient, and they may
even stand for local divisions in the strata, but they are bounded by no
actual gaps in the sweep of terrestrial events.

Moreover, it must be understood that the "ages" of different continents,
though described under the same name, are not necessarily of exact
contemporaneity. There is no sure test available by which it could be shown
that the Devonian age, for instance, as outlined in the strata of Europe, did
not begin millions of years earlier or later than the period whose records are
said to represent the Devonian age in America. In attempting to decide such
details as this, mineralogical data fail us utterly. Even in rocks of adjoining
regions identity of structure is no proof of contemporaneous origin; for the
veritable substance of the rock of one age is ground up to build the rocks of
subsequent ages. Furthermore, in seas where conditions change but little the
same form of rock may be made age after age. It is believed that chalk-beds
still forming in some of our present seas may form one continuous mass
dating back to earliest geologic ages. On the other hand, rocks different in
character maybe formed at the same time in regions not far apart—say a
sandstone along shore, a coral limestone farther seaward, and a chalk-bed
beyond. This continuous stratum, broken in the process of upheaval, might
seem the record of three different epochs.
Paleontology, of course, supplies far better chronological tests, but even
these have their limitations. There has been no time since rocks now in
existence were formed, if ever, when the earth had a uniform climate and a
single undiversified fauna over its entire land surface, as the early
paleontologists supposed. Speaking broadly, the same general stages have
attended the evolution of organic forms everywhere, but there is nothing to
show that equal periods of time witnessed corresponding changes in diverse
regions, but quite the contrary. To cite but a single illustration, the marsupial
order, which is the dominant mammalian type of the living fauna of
Australia to-day, existed in Europe and died out there in the tertiary age.
Hence a future geologist might think the Australia of to-day
contemporaneous with a period in Europe which in reality antedated it by
perhaps millions of years.
All these puzzling features unite to render the subject of historical
geology anything but the simple matter the fathers of the science esteemed
it. No one would now attempt to trace the exact sequence of formation of all
the mountains of the globe, as Elie de Beaumont did a half-century ago.
Even within the limits of a single continent, the geologist must proceed with
much caution in attempting to chronicle the order in which its various parts
rose from the matrix of the sea. The key to this story is found in the

identification of the strata that are the surface feature in each territory. If
Devonian rocks are at the surface in any given region, for example, it would
appear that this region became a land surface in the Devonian age, or just
afterwards. But a moment's consideration shows that there is an element of
uncertainty about this, due to the steady denudation that all land surfaces
undergo. The Devonian rocks may lie at the surface simply because the
thousands of feet of carboniferous strata that once lay above them have
been worn away. All that the cautious geologist dare assert, therefore, is that
the region in question did not become permanent land surface earlier than
the Devonian age.
But to know even this is much—sufficient, indeed, to establish the
chronological order of elevation, if not its exact period, for all parts of any
continent that have been geologically explored—understanding always that
there must be no scrupling about a latitude of a few millions or perhaps tens
of millions of years here and there.
Regarding our own continent, for example, we learn through the
researches of a multitude of workers that in the early day it was a mere
archipelago. Its chief island—the backbone of the future continent—was a
great V-shaped area surrounding what is now Hudson Bay, an area built tip,
perhaps, through denudation of a yet more ancient polar continent, whose
existence is only conjectured. To the southeast an island that is now the
Adirondack Mountains, and another that is now the Jersey Highlands rose
above the waste of waters, and far to the south stretched probably a line of
islands now represented by the Blue Ridge Mountains. Far off to the
westward another line of islands foreshadowed our present Pacific border. A
few minor islands in the interior completed the archipelago.
From this bare skeleton the continent grew, partly by the deposit of
sediment from the denudation of the original islands (which once towered
miles, perhaps, where now they rise thousands of feet), but largely also by
the deposit of organic remains, especially in the interior sea, which teemed
with life. In the Silurian ages, invertebrates—brachiopods and crinoids and
cephalopods—were the dominant types. But very early—no one knows just
when—there came fishes of many strange forms, some of the early ones
enclosed in turtle-like shells. Later yet, large spaces within the interior sea
having risen to the surface, great marshes or forests of strange types of
vegetation grew and deposited their remains to form coal-beds. Many times

over such forests were formed, only to be destroyed by the oscillations of
the land surface. All told, the strata of this Paleozoic period aggregate
several miles in thickness, and the time consumed in their formation stands
to all later time up to the present, according to Professor Dana's estimate, as
three to one.
Towards the close of this Paleozoic era the Appalachian Mountains were
slowly upheaved in great convoluted folds, some of them probably reaching
three or four miles above the sea-level, though the tooth of time has since
gnawed them down to comparatively puny limits. The continental areas
thus enlarged were peopled during the ensuing Mesozoic time with
multitudes of strange reptiles, many of them gigantic in size. The waters,
too, still teeming with invertebrates and fishes, had their quota of reptilian
monsters; and in the air were flying reptiles, some of which measured
twenty-five feet from tip to tip of their batlike wings. During this era the
Sierra Nevada Mountains rose. Near the eastern border of the forming
continent the strata were perhaps now too thick and stiff to bend into
mountain folds, for they were rent into great fissures, letting out floods of
molten lava, remnants of which are still in evidence after ages of
denudation, as the Palisades along the Hudson, and such elevations as
Mount Holyoke in western Massachusetts.
Still there remained a vast interior sea, which later on, in the tertiary age,
was to be divided by the slow uprising of the land, which only yesterday—
that is to say, a million, or three or five or ten million, years ago—became
the Rocky Mountains. High and erect these young mountains stand to this
day, their sharp angles and rocky contours vouching for their youth, in
strange contrast with the shrunken forms of the old Adirondacks, Green
Mountains, and Appalachians, whose lowered heads and rounded shoulders
attest the weight of ages. In the vast lakes which still remained on either
side of the Rocky range, tertiary strata were slowly formed to the ultimate
depth of two or three miles, enclosing here and there those vertebrate
remains which were to be exposed again to view by denudation when the
land rose still higher, and then, in our own time, to tell so wonderful a story
to the paleontologist.
Finally, the interior seas were filled, and the shore lines of the continent
assumed nearly their present outline.

Then came the long winter of the glacial epoch—perhaps of a succession
of glacial epochs. The ice sheet extended southward to about the fortieth
parallel, driving some animals before it, and destroying those that were
unable to migrate. At its fulness, the great ice mass lay almost a mile in
depth over New England, as attested by the scratched and polished rock
surfaces and deposited erratics in the White Mountains. Such a mass presses
down with a weight of about one hundred and twenty-five tons to the square
foot, according to Dr. Croll's estimate. It crushed and ground everything
beneath it more or less, and in some regions planed off hilly surfaces into
prairies. Creeping slowly forward, it carried all manner of debris with it.
When it melted away its terminal moraine built up the nucleus of the land
masses now known as Long Island and Staten Island; other of its deposits
formed the "drumlins" about Boston famous as Bunker and Breed's hills;
and it left a long, irregular line of ridges of "till" or bowlder clay and
scattered erratics clear across the country at about the latitude of New York
city.
As the ice sheet slowly receded it left minor moraines all along its
course. Sometimes its deposits dammed up river courses or inequalities in
the surface, to form the lakes which everywhere abound over Northern
territories. Some glacialists even hold the view first suggested by Ramsey,
of the British Geological Survey, that the great glacial sheets scooped out
the basins of many lakes, including the system that feeds the St. Lawrence.
At all events, it left traces of its presence all along the line of its retreat, and
its remnants exist to this day as mountain glaciers and the polar ice cap.
Indeed, we live on the border of the last glacial epoch, for with the closing
of this period the long geologic past merges into the present.
PAST, PRESENT, AND FUTURE
And the present, no less than the past, is a time of change. This is the
thought which James Hutton conceived more than a century ago, but which
his contemporaries and successors were so very slow to appreciate. Now,
however, it has become axiomatic—one can hardly realize that it was ever
doubted. Every new scientific truth, says Agassiz, must pass through three
stages—first, men say it is not true; then they declare it hostile to religion;
finally, they assert that every one has known it always. Hutton's truth that
natural law is changeless and eternal has reached this final stage. Nowhere
now could you find a scientist who would dispute the truth of that text

which Lyell, quoting from Playfair's Illustrations of the Huttonian Theory,
printed on the title-page of his Principles: "Amid all the revolutions of the
globe the economy of Nature has been uniform, and her laws are the only
things that have resisted the general movement. The rivers and the rocks,
the seas and the continents, have been changed in all their parts; but the
laws which direct those changes, and the rules to which they are subject,
have remained invariably the same."
But, on the other hand, Hutton and Playfair, and in particular Lyell, drew
inferences from this principle which the modern physicist can by no means
admit. To them it implied that the changes on the surface of the earth have
always been the same in degree as well as in kind, and must so continue
while present forces hold their sway. In other words, they thought of the
world as a great perpetual-motion machine. But the modern physicist, given
truer mechanical insight by the doctrines of the conservation and the
dissipation of energy, will have none of that. Lord Kelvin, in particular, has
urged that in the periods of our earth's in fancy and adolescence its
developmental changes must have been, like those of any other infant
organism, vastly more rapid and pronounced than those of a later day; and
to every clear thinker this truth also must now seem axiomatic.
Whoever thinks of the earth as a cooling globe can hardly doubt that its
crust, when thinner, may have heaved under strain of the moon's tidal pull
—whether or not that body was nearer—into great billows, daily rising and
falling, like waves of the present seas vastly magnified.
Under stress of that same lateral pressure from contraction which now
produces the slow depression of the Jersey coast, the slow rise of Sweden,
the occasional belching of an insignificant volcano, the jetting of a geyser,
or the trembling of an earthquake, once large areas were rent in twain, and
vast floods of lava flowed over thousands of square miles of the earth's
surface, perhaps, at a single jet; and, for aught we know to the contrary,
gigantic mountains may have heaped up their contorted heads in cataclysms
as spasmodic as even the most ardent catastrophist of the elder day of
geology could have imagined.
The atmosphere of that early day, filled with vast volumes of carbon,
oxygen, and other chemicals that have since been stored in beds of coal,
limestone, and granites, may have worn down the rocks on the one hand

and built up organic forms on the other, with a rapidity that would now
seem hardly conceivable.
And yet while all these anomalous things went on, the same laws held
sway that now are operative; and a true doctrine of uniformitarianism would
make no unwonted concession in conceding them all—though most of the
imbittered geological controversies of the middle of the nineteenth century
were due to the failure of both parties to realize that simple fact.
And as of the past and present, so of the future. The same forces will
continue to operate; and under operation of these unchanging forces each
day will differ from every one that has preceded it. If it be true, as every
physicist believes, that the earth is a cooling globe, then, whatever its
present stage of refrigeration, the time must come when its surface contour
will assume a rigidity of level not yet attained. Then, just as surely, the slow
action of the elements will continue to wear away the land surfaces, particle
by particle, and transport them to the ocean, as it does to-day, until,
compensation no longer being afforded by the upheaval of the continents,
the last foot of dry land will sink for the last time beneath the water, the last
mountain-peak melting away, and our globe, lapsing like any other
organism into its second childhood, will be on the surface—as presumably
it was before the first continent rose—one vast "waste of waters." As puny
man conceives time and things, an awful cycle will have lapsed; in the
sweep of the cosmic life, a pulse-beat will have throbbed.

V. THE NEW SCIENCE OF METEOROLOGY
METEORITES
"An astonishing miracle has just occurred in our district," wrote M.
Marais, a worthy if undistinguished citizen of France, from his home at
L'Aigle, under date of "the 13th Floreal, year 11"—a date which outside of
France would be interpreted as meaning May 3, 1803. This "miracle" was
the appearance of a "fireball" in broad daylight—"perhaps it was wildfire,"
says the naive chronicle—which "hung over the meadow," being seen by
many people, and then exploded with a loud sound, scattering thousands of
stony fragments over the surface of a territory some miles in extent.
Such a "miracle" could not have been announced at a more opportune
time. For some years the scientific world had been agog over the question
whether such a form of lightning as that reported—appearing in a clear sky,
and hurling literal thunderbolts—had real existence. Such cases had been
reported often enough, it is true. The "thunderbolts" themselves were
exhibited as sacred relics before many an altar, and those who doubted their
authenticity had been chided as having "an evil heart of unbelief." But
scientific scepticism had questioned the evidence, and late in the eighteenth
century a consensus of opinion in the French Academy had declined to
admit that such stones had been "conveyed to the earth by lightning," let
alone any more miraculous agency.
In 1802, however, Edward Howard had read a paper before the Royal
Society in which, after reviewing the evidence recently put forward, he had
reached the conclusion that the fall of stones from the sky, sometimes or
always accompanied by lightning, must be admitted as an actual
phenomenon, however inexplicable. So now, when the great stone-fall at
L'Aigle was announced, the French Academy made haste to send the
brilliant young physicist Jean Baptiste Biot to investigate it, that the matter
might, if possible, be set finally at rest. The investigation was in all respects
successful, and Biot's report transferred the stony or metallic lightning-bolt
—the aerolite or meteorite—from the realm of tradition and conjecture to
that of accepted science.

But how explain this strange phenomenon? At once speculation was rife.
One theory contended that the stony masses had not actually fallen, but had
been formed from the earth by the action of the lightning; but this
contention was early abandoned. The chemists were disposed to believe that
the aerolites had been formed by the combination of elements floating in
the upper atmosphere. Geologists, on the other hand, thought them of
terrestrial origin, urging that they might have been thrown up by volcanoes.
The astronomers, as represented by Olbers and Laplace, modified this
theory by suggesting that the stones might, indeed, have been cast out by
volcanoes, but by volcanoes situated not on the earth, but on the moon.
And one speculator of the time took a step even more daring, urging that
the aerolites were neither of telluric nor selenitic origin, nor yet children of
the sun, as the old Greeks had, many of them, contended, but that they are
visitants from the depths of cosmic space. This bold speculator was the
distinguished German physicist Ernst F. F. Chladni, a man of no small
repute in his day. As early as 1794 he urged his cosmical theory of
meteorites, when the very existence of meteorites was denied by most
scientists. And he did more: he declared his belief that these falling stones
were really one in origin and kind with those flashing meteors of the upper
atmosphere which are familiar everywhere as "shooting-stars."
Each of these coruscating meteors, he affirmed, must tell of the ignition
of a bit of cosmic matter entering the earth's atmosphere. Such wandering
bits of matter might be the fragments of shattered worlds, or, as Chladni
thought more probable, merely aggregations of "world stuff" never hitherto
connected with any large planetary mass.
Naturally enough, so unique a view met with very scant favor.
Astronomers at that time saw little to justify it; and the non-scientific world
rejected it with fervor as being "atheistic and heretical," because its
acceptance would seem to imply that the universe is not a perfect
mechanism.
Some light was thrown on the moot point presently by the observations
of Brandes and Benzenberg, which tended to show that falling-stars travel
at an actual speed of from fifteen to ninety miles a second. This observation
tended to discredit the selenitic theory, since an object, in order to acquire
such speed in falling merely from the moon, must have been projected with
an initial velocity not conceivably to be given by any lunar volcanic

impulse. Moreover, there was a growing conviction that there are no active
volcanoes on the moon, and other considerations of the same tenor led to
the complete abandonment of the selenitic theory.
But the theory of telluric origin of aerolites was by no means so easily
disposed of. This was an epoch when electrical phenomena were exciting
unbounded and universal interest, and there was a not unnatural tendency to
appeal to electricity in explanation of every obscure phenomenon; and in
this case the seeming similarity between a lightning flash and the flash of an
aerolite lent color to the explanation. So we find Thomas Forster, a
meteorologist of repute, still adhering to the atmospheric theory of
formation of aerolites in his book published in 1823; and, indeed, the
prevailing opinion of the time seemed divided between various telluric
theories, to the neglect of any cosmical theory whatever.
But in 1833 occurred a phenomenon which set the matter finally at rest.
A great meteoric shower occurred in November of that year, and in
observing it Professor Denison Olmstead, of Yale, noted that all the stars of
the shower appeared to come from a single centre or vanishing-point in the
heavens, and that this centre shifted its position with the stars, and hence
was not telluric. The full significance of this observation was at once
recognized by astronomers; it demonstrated beyond all cavil the cosmical
origin of the shooting-stars. Some conservative meteorologists kept up the
argument for the telluric origin for some decades to come, as a matter of
course—such a band trails always in the rear of progress. But even these
doubters were silenced when the great shower of shooting-stars appeared
again in 1866, as predicted by Olbers and Newton, radiating from the same
point of the heavens as before.
Since then the spectroscope has added its confirmatory evidence as to the
identity of meteorite and shooting-star, and, moreover, has linked these
atmospheric meteors with such distant cosmic residents as comets and
nebulae. Thus it appears that Chladni's daring hypothesis of 1794 has been
more than verified, and that the fragments of matter dissociated from
planetary connection—which be postulated and was declared atheistic for
postulating—have been shown to be billions of times more numerous than
any larger cosmic bodies of which we have cognizance—so widely does the
existing universe differ from man's preconceived notions as to what it
should be.

Thus also the "miracle" of the falling stone, against which the scientific
scepticism of yesterday presented "an evil heart of unbelief," turns out to be
the most natural phenomena, inasmuch as it is repeated in our atmosphere
some millions of times each day.
THE AURORA BOREALIS
If fire-balls were thought miraculous and portentous in days of yore,
what interpretation must needs have been put upon that vastly more
picturesque phenomenon, the aurora? "Through all the city," says the Book
of Maccabees, "for the space of almost forty days, there were seen
horsemen running in the air, in cloth of gold, armed with lances, like a band
of soldiers: and troops of horsemen in array encountering and running one
against another, with shaking of shields and multitude of pikes, and drawing
of swords, and casting of darts, and glittering of golden ornaments and
harness." Dire omens these; and hardly less ominous the aurora seemed to
all succeeding generations that observed it down well into the eighteenth
century—as witness the popular excitement in England in 1716 over the
brilliant aurora of that year, which became famous through Halley's
description.
But after 1752, when Franklin dethroned the lightning, all spectacular
meteors came to be regarded as natural phenomena, the aurora among the
rest. Franklin explained the aurora—which was seen commonly enough in
the eighteenth century, though only recorded once in the seventeenth—as
due to the accumulation of electricity on the surface of polar snows, and its
discharge to the equator through the upper atmosphere. Erasmus Darwin
suggested that the luminosity might be due to the ignition of hydrogen,
which was supposed by many philosophers to form the upper atmosphere.
Dalton, who first measured the height of the aurora, estimating it at about
one hundred miles, thought the phenomenon due to magnetism acting on
ferruginous particles in the air, and his explanation was perhaps the most
popular one at the beginning of the last century.
Since then a multitude of observers have studied the aurora, but the
scientific grasp has found it as elusive in fact as it seems to casual
observation, and its exact nature is as undetermined to-day as it was a
hundred years ago. There has been no dearth of theories concerning it,
however. Blot, who studied it in the Shetland Islands in 1817, thought it due
to electrified ferruginous dust, the origin of which he ascribed to Icelandic

volcanoes. Much more recently the idea of ferruginous particles has been
revived, their presence being ascribed not to volcanoes, but to the
meteorites constantly being dissipated in the upper atmosphere. Ferruginous
dust, presumably of such origin, has been found on the polar snows, as well
as on the snows of mountain-tops, but whether it could produce the
phenomena of auroras is at least an open question.
Other theorists have explained the aurora as due to the accumulation of
electricity on clouds or on spicules of ice in the upper air. Yet others think it
due merely to the passage of electricity through rarefied air itself. Humboldt
considered the matter settled in yet another way when Faraday showed, in
1831, that magnetism may produce luminous effects. But perhaps the
prevailing theory of to-day assumes that the aurora is due to a current of
electricity generated at the equator and passing through upper regions of
space, to enter the earth at the magnetic poles—simply reversing the course
which Franklin assumed.
The similarity of the auroral light to that generated in a vacuum bulb by
the passage of electricity lends support to the long-standing supposition that
the aurora is of electrical origin, but the subject still awaits complete
elucidation. For once even that mystery-solver the spectroscope has been
baffled, for the line it sifts from the aurora is not matched by that of any
recognized substance. A like line is found in the zodiacal light, it is true, but
this is of little aid, for the zodiacal light, though thought by some
astronomers to be due to meteor swarms about the sun, is held to be, on the
whole, as mysterious as the aurora itself.
Whatever the exact nature of the aurora, it has long been known to be
intimately associated with the phenomena of terrestrial magnetism.
Whenever a brilliant aurora is visible, the world is sure to be visited with
what Humboldt called a magnetic storm—a "storm" which manifests itself
to human senses in no way whatsoever except by deflecting the magnetic
needle and conjuring with the electric wire. Such magnetic storms are
curiously associated also with spots on the sun—just how no one has
explained, though the fact itself is unquestioned. Sun-spots, too, seem
directly linked with auroras, each of these phenomena passing through
periods of greatest and least frequency in corresponding cycles of about
eleven years' duration.

It was suspected a full century ago by Herschel that the variations in the
number of sun-spots had a direct effect upon terrestrial weather, and he
attempted to demonstrate it by using the price of wheat as a criterion of
climatic conditions, meantime making careful observation of the sun-spots.
Nothing very definite came of his efforts in this direction, the subject being
far too complex to be determined without long periods of observation.
Latterly, however, meteorologists, particularly in the tropics, are disposed to
think they find evidence of some such connection between sun-spots and
the weather as Herschel suspected. Indeed, Mr. Meldrum declares that there
is a positive coincidence between periods of numerous sun-spots and
seasons of excessive rain in India.
That some such connection does exist seems intrinsically probable. But
the modern meteorologist, learning wisdom of the past, is extremely
cautious about ascribing casual effects to astronomical phenomena. He
finds it hard to forget that until recently all manner of climatic conditions
were associated with phases of the moon; that not so very long ago showers
of falling-stars were considered "prognostic" of certain kinds of weather;
and that the "equinoctial storm" had been accepted as a verity by every one,
until the unfeeling hand of statistics banished it from the earth.
Yet, on the other hand, it is easily within the possibilities that the science
of the future may reveal associations between the weather and sun-spots,
auroras, and terrestrial magnetism that as yet are hardly dreamed of. Until
such time, however, these phenomena must feel themselves very grudgingly
admitted to the inner circle of meteorology. More and more this science
concerns itself, in our age of concentration and specialization, with weather
and climate. Its votaries no longer concern themselves with stars or planets
or comets or shooting-stars—once thought the very essence of guides to
weather wisdom; and they are even looking askance at the moon, and
asking her to show cause why she also should not be excluded from their
domain. Equally little do they care for the interior of the earth, since they
have learned that the central emanations of heat which Mairan imagined as
a main source of aerial warmth can claim no such distinction. Even such
problems as why the magnetic pole does not coincide with the
geographical, and why the force of terrestrial magnetism decreases from the
magnetic poles to the magnetic equator, as Humboldt first discovered that it
does, excite them only to lukewarm interest; for magnetism, they say, is not
known to have any connection whatever with climate or weather.

EVAPORATION, CLOUD FORMATION, AND DEW
There is at least one form of meteor, however, of those that interested our
forebears whose meteorological importance they did not overestimate. This
is the vapor of water. How great was the interest in this familiar meteor at
the beginning of the century is attested by the number of theories then
extant regarding it; and these conflicting theories bear witness also to the
difficulty with which the familiar phenomenon of the evaporation of water
was explained.
Franklin had suggested that air dissolves water much as water dissolves
salt, and this theory was still popular, though Deluc had disproved it by
showing that water evaporates even more rapidly in a vacuum than in air.
Deluc's own theory, borrowed from earlier chemists, was that evaporation is
the chemical union of particles of water with particles of the supposititious
element heat. Erasmus Darwin combined the two theories, suggesting that
the air might hold a variable quantity of vapor in mere solution, and in
addition a permanent moiety in chemical combination with caloric.
Undisturbed by these conflicting views, that strangely original genius,
John Dalton, afterwards to be known as perhaps the greatest of theoretical
chemists, took the question in hand, and solved it by showing that water
exists in the air as an utterly independent gas. He reached a partial insight
into the matter in 1793, when his first volume of meteorological essays was
published; but the full elucidation of the problem came to him in 1801. The
merit of his studies was at once recognized, but the tenability of his
hypothesis was long and ardently disputed.
While the nature of evaporation was in dispute, as a matter of course the
question of precipitation must be equally undetermined. The most famous
theory of the period was that formulated by Dr. Hutton in a paper read
before the Royal Society of Edinburgh, and published in the volume of
transactions which contained also the same author's epoch-making paper on
geology. This "theory of rain" explained precipitation as due to the cooling
of a current of saturated air by contact with a colder current, the assumption
being that the surplusage of moisture was precipitated in a chemical sense,
just as the excess of salt dissolved in hot water is precipitated when the
water cools. The idea that the cooling of the saturated air causes the
precipitation of its moisture is the germ of truth that renders this paper of
Hutton's important. All correct later theories build on this foundation.

"Let us suppose the surface of this earth wholly covered with water," said
Hutton, "and that the sun were stationary, being always vertical in one
place; then, from the laws of heat and rarefaction, there would be formed a
circulation in the atmosphere, flowing from the dark and cold hemisphere to
the heated and illuminated place, in all directions, towards the place of the
greatest cold.
"As there is for the atmosphere of this earth a constant cooling cause, this
fluid body could only arrive at a certain degree of heat; and this would be
regularly decreasing from the centre of illumination to the opposite point of
the globe, most distant from the light and heat. Between these two regions
of extreme heat and cold there would, in every place, be found two streams
of air following in opposite directions. If those streams of air, therefore,
shall be supposed as both sufficiently saturated with humidity, then, as they
are of different temperatures, there would be formed a continual
condensation of aqueous vapor, in some middle region of the atmosphere,
by the commixtion of part of those two opposite streams.
"Hence there is reason to believe that in this supposed case there would
be formed upon the surface of the globe three different regions—the torrid
region, the temperate, and the frigid. These three regions would continue
stationary; and the operations of each would be continual. In the torrid
region, nothing but evaporation and heat would take place; no cloud could
be formed, because in changing the transparency of the atmosphere to
opacity it would be heated immediately by the operation of light, and thus
the condensed water would be again evaporated. But this power of the sun
would have a termination; and it is these that would begin the region of
temperate heat and of continual rain. It is not probable that the region of
temperance would reach far beyond the region of light; and in the
hemisphere of darkness there would be found a region of extreme cold and
perfect dryness.
"Let us now suppose the earth as turning on its axis in the equinoctial
situation. The torrid region would thus be changed into a zone, in which
there would be night and day; consequently, here would be much
temperance, compared with the torrid region now considered; and here
perhaps there would be formed periodical condensation and evaporation of
humidity, corresponding to the seasons of night and day. As temperance
would thus be introduced into the region of torrid extremity, so would the

effect of this change be felt over all the globe, every part of which would
now be illuminated, consequently heated in some degree. Thus we would
have a line of great heat and evaporation, graduating each way into a point
of great cold and congelation. Between these two extremes of heat and cold
there would be found in each hemisphere a region of much temperance, in
relation to heat, but of much humidity in the atmosphere, perhaps of
continual rain and condensation.
"The supposition now formed must appear extremely unfit for making
this globe a habitable world in every part; but having thus seen the effect of
night and day in temperating the effects of heat and cold in every place, we
are now prepared to contemplate the effects of supposing this globe to
revolve around the sun with a certain inclination of its axis. By this
beautiful contrivance, that comparatively uninhabited globe is now divided
into two hemispheres, each of which is thus provided with a summer and a
winter season. But our present view is limited to the evaporation and
condensation of humidity; and, in this contrivance of the seasons, there
must appear an ample provision for those alternate operations in every part;
for as the place of the vertical sun is moved alternately from one tropic to
the other, heat and cold, the original causes of evaporation and
condensation, must be carried over all the globe, producing either annual
seasons of rain or diurnal seasons of condensation and evaporation, or both
these seasons, more or less—that is, in some degree.
"The original cause of motion in the atmosphere is the influence of the
sun heating the surface of the earth exposed to that luminary. We have not
supposed that surface to have been of one uniform shape and similar
substance; from whence it has followed that the annual propers of the sun,
perhaps also the diurnal propers, would produce a regular condensation of
rain in certain regions, and the evaporation of humidity in others; and this
would have a regular progress in certain determined seasons, and would not
vary. But nothing can be more distant from this supposition, that is the
natural constitution of the earth; for the globe is composed of sea and land,
in no regular shape or mixture, while the surface of the land is also irregular
with respect to its elevations and depressions, and various with regard to the
humidity and dryness of that part which is exposed to heat as the cause of
evaporation. Hence a source of the most valuable motions in the fluid
atmosphere with aqueous vapor, more or less, so far as other natural
operations will admit; and hence a source of the most irregular commixture

of the several parts of this elastic fluid, whether saturated or not with
aqueous vapor.
"According to the theory, nothing is required for the production of rain
besides the mixture of portions of the atmosphere with humidity, and of
mixing the parts that are in different degrees of heat. But we have seen the
causes of saturating every portion of the atmosphere with humidity and of
mixing the parts which are in different degrees of heat. Consequently, over
all the surface of the globe there should happen occasionally rain and
evaporation, more or less; and also, in every place, those vicissitudes should
be observed to take place with some tendency to regularity, which,
however, may be so disturbed as to be hardly distinguishable upon many
occasions. Variable winds and variable rains should be found in proportion
as each place is situated in an irregular mixture of land and water; whereas
regular winds should be found in proportion to the uniformity of the
surface; and regular rains in proportion to the regular changes of those
winds by which the mixture of the atmosphere necessary to the rain may be
produced. But as it will be acknowledged that this is the case in almost all
this earth where rain appears according to the conditions here specified, the
theory is found to be thus in conformity with nature, and natural
appearances are thus explained by the theory."(1)
The next ambitious attempt to explain the phenomena of aqueous
meteors was made by Luke Howard, in his remarkable paper on clouds,
published in the Philosophical Magazine in 1803—the paper in which the
names cirrus, cumulus, stratus, etc., afterwards so universally adopted, were
first proposed. In this paper Howard acknowledges his indebtedness to
Dalton for the theory of evaporation; yet he still clings to the idea that the
vapor, though independent of the air, is combined with particles of caloric.
He holds that clouds are composed of vapor that has previously risen from
the earth, combating the opinions of those who believe that they are formed
by the union of hydrogen and oxygen existing independently in the air;
though he agrees with these theorists that electricity has entered largely into
the modus operandi of cloud formation. He opposes the opinion of Deluc
and De Saussure that clouds are composed of particles of water in the form
of hollow vesicles (miniature balloons, in short, perhaps filled with
hydrogen), which untenable opinion was a revival of the theory as to the
formation of all vapor which Dr. Halley had advocated early in the
eighteenth century.

Of particular interest are Howard's views as to the formation of dew,
which he explains as caused by the particles of caloric forsaking the vapor
to enter the cool body, leaving the water on the surface. This comes as near
the truth, perhaps, as could be expected while the old idea as to the
materiality of heat held sway. Howard believed, however, that dew is
usually formed in the air at some height, and that it settles to the surface,
opposing the opinion, which had gained vogue in France and in America
(where Noah Webster prominently advocated it), that dew ascends from the
earth.
The complete solution of the problem of dew formation—which really
involved also the entire question of precipitation of watery vapor in any
form—was made by Dr. W. C. Wells, a man of American birth, whose life,
however, after boyhood, was spent in Scotland (where as a young man he
enjoyed the friendship of David Hume) and in London. Inspired, no doubt,
by the researches of Mack, Hutton, and their confreres of that Edinburgh
school, Wells made observations on evaporation and precipitation as early
as 1784, but other things claimed his attention; and though he asserts that
the subject was often in his mind, he did not take it up again in earnest until
about 1812.
Meantime the observations on heat of Rumford and Davy and Leslie had
cleared the way for a proper interpretation of the facts—about the facts
themselves there had long been practical unanimity of opinion. Dr. Black,
with his latent-heat observations, had really given the clew to all subsequent
discussions of the subject of precipitation of vapor; and from this time on it
had been known that heat is taken up when water evaporates, and given out
again when it condenses. Dr. Darwin had shown in 1788, in a paper before
the Royal Society, that air gives off heat on contracting and takes it up on
expanding; and Dalton, in his essay of 1793, had explained this
phenomenon as due to the condensation and vaporization of the water
contained in the air.
But some curious and puzzling observations which Professor Patrick
Wilson, professor of astronomy in the University of Glasgow, had
communicated to the Royal Society of Edinburgh in 1784, and some similar
ones made by Mr. Six, of Canterbury, a few years later, had remained
unexplained. Both these gentlemen observed that the air is cooler where
dew is forming than the air a few feet higher, and they inferred that the dew

in forming had taken up heat, in apparent violation of established physical
principles.
It remained for Wells, in his memorable paper of 1816, to show that these
observers had simply placed the cart before the horse. He made it clear that
the air is not cooler because the dew is formed, but that the dew is formed
because the air is cooler—having become so through radiation of heat from
the solids on which the dew forms. The dew itself, in forming, gives out its
latent heat, and so tends to equalize the temperature.
Wells's paper is so admirable an illustration of the lucid presentation of
clearly conceived experiments and logical conclusions that we should do it
injustice not to present it entire. The author's mention of the observations of
Six and Wilson gives added value to his own presentation.
Dr. Wells's Essay on Dew
"I was led in the autumn of 1784, by the event of a rude experiment, to
think it probable that the formation of dew is attended with the production
of cold. In 1788, a paper on hoar-frost, by Mr. Patrick Wilson, of Glasgow,
was published in the first volume of the Transactions of the Royal Society
of Edinburgh, by which it appeared that this opinion bad been entertained
by that gentleman before it had occurred to myself. In the course of the
same year, Mr. Six, of Canterbury, mentioned in a paper communicated to
the Royal Society that on clear and dewy nights he always found the
mercury lower in a thermometer laid upon the ground in a meadow in his
neighborhood than it was in a similar thermometer suspended in the air six
feet above the former; and that upon one night the difference amounted to
five degrees of Fahrenheit's scale. Mr. Six, however, did not suppose,
agreeably to the opinion of Mr. Wilson and myself, that the cold was
occasioned by the formation of dew, but imagined that it proceeded partly
from the low temperature of the air, through which the dew, already formed
in the atmosphere, had descended, and partly from the evaporation of
moisture from the ground, on which his thermometer had been placed. The
conjecture of Mr. Wilson and the observations of Mr. Six, together with
many facts which I afterwards learned in the course of reading,
strengthened my opinion; but I made no attempt, before the autumn of
1811, to ascertain by experiment if it were just, though it had in the mean
time almost daily occurred to my thoughts. Happening, in that season, to be
in that country in a clear and calm night, I laid a thermometer upon grass

wet with dew, and suspended a second in the air, two feet above the other.
An hour afterwards the thermometer on the grass was found to be eight
degrees lower, by Fahrenheit's division, than the one in the air. Similar
results having been obtained from several similar experiments, made during
the same autumn, I determined in the next spring to prosecute the subject
with some degree of steadiness, and with that view went frequently to the
house of one of my friends who lives in Surrey.
"At the end of two months I fancied that I had collected information
worthy of being published; but, fortunately, while preparing an account of it
I met by accident with a small posthumous work by Mr. Six, printed at
Canterbury in 1794, in which are related differences observed on dewy
nights between thermometers placed upon grass and others in the air that
are much greater than those mentioned in the paper presented by him to the
Royal Society in 1788. In this work, too, the cold of the grass is attributed,
in agreement with the opinion of Mr. Wilson, altogether to the dew
deposited upon it. The value of my own observations appearing to me now
much diminished, though they embraced many points left untouched by Mr.
Six, I gave up my intentions of making them known. Shortly after, however,
upon considering the subject more closely, I began to suspect that Mr.
Wilson, Mr. Six, and myself had all committed an error regarding the cold
which accompanies dew as an effect of the formation of that fluid. I
therefore resumed my experiments, and having by means of them, I think,
not only established the justness of my suspicions, but ascertained the real
cause both of dew and of several other natural appearances which have
hitherto received no sufficient explanation, I venture now to submit to the
consideration of the learned an account of some of my labors, without
regard to the order of time in which they were performed, and of various
conclusions which may be drawn from them, mixed with facts and opinions
already published by others:
"There are various occurrences in nature which seem to me strictly allied
to dew, though their relation to it be not always at first sight perceivable.
The statement and explanation of several of these will form the concluding
part of the present essay.
"1. I observed one morning, in winter, that the insides of the panes of
glass in the windows of my bedchamber were all of them moist, but that
those which had been covered by an inside shutter during the night were

much more so than the others which had been uncovered. Supposing that
this diversity of appearance depended upon a difference of temperature, I
applied the naked bulbs of two delicate thermometers to a covered and
uncovered pane; on which I found that the former was three degrees colder
than the latter. The air of the chamber, though no fire was kept in it, was at
this time eleven and one-half degrees warmer than that without. Similar
experiments were made on many other mornings, the results of which were
that the warmth of the internal air exceeded that of the external from eight
to eighteen degrees, the temperature of the covered panes would be from
one to five degrees less than the uncovered; that the covered were
sometimes dewed, while the uncovered were dry; that at other times both
were free from moisture; that the outsides of the covered and uncovered
panes had similar differences with respect to heat, though not so great as
those of the inner surfaces; and that no variation in the quantity of these
differences was occasioned by the weather's being cloudy or fair, provided
the heat of the internal air exceeded that of the external equally in both of
those states of the atmosphere.
"The remote reason of these differences did not immediately present
itself. I soon, however, saw that the closed shutter shielded the glass which
it covered from the heat that was radiated to the windows by the walls and
furniture of the room, and thus kept it nearer to the temperature of the
external air than those parts could be which, from being uncovered,
received the heat emitted to them by the bodies just mentioned.
"In making these experiments, I seldom observed the inside of any pane
to be more than a little damped, though it might be from eight to twelve
degrees colder than the general mass of the air in the room; while, in the
open air, I had often found a great dew to form on substances only three or
four degrees colder than the atmosphere. This at first surprised me; but the
cause now seems plain. The air of the chamber had once been a portion of
the external atmosphere, and had afterwards been heated, when it could
receive little accessories to its original moisture. It constantly required
being cooled considerably before it was even brought back to its former
nearness to repletion with water; whereas the whole external air is
commonly, at night, nearly replete with moisture, and therefore readily
precipitates dew on bodies only a little colder than itself.

"When the air of a room is warmer than the external atmosphere, the
effect of an outside shutter on the temperature of the glass of the window
will be directly opposite to what has just been stated; since it must prevent
the radiation, into the atmosphere, of the heat of the chamber transmitted
through the glass.
"2. Count Rumford appears to have rightly conjectured that the
inhabitants of certain hot countries, who sleep at nights on the tops of their
houses, are cooled during this exposure by the radiation of their heat to the
sky; or, according to his manner of expression, by receiving frigorific rays
from the heavens. Another fact of this kind seems to be the greater chill
which we often experience upon passing at night from the cover of a house
into the air than might have been expected from the cold of the external
atmosphere. The cause, indeed, is said to be the quickness of transition from
one situation to another. But if this were the whole reason, an equal chill
would be felt in the day, when the difference, in point of heat, between the
internal and external air was the same as at night, which is not the case.
Besides, if I can trust my own observation, the feeling of cold from this
cause is more remarkable in a clear than in a cloudy night, and in the
country than in towns. The following appears to be the manner in which
these things are chiefly to be explained:
"During the day our bodies while in the open air, although not
immediately exposed to the sun's rays, are yet constantly deriving heat from
them by means of the reflection of the atmosphere. This heat, though it
produces little change on the temperature of the air which it traverses,
affords us some compensation for the heat which we radiate to the heavens.
At night, also, if the sky be overcast, some compensation will be made to
us, both in the town and in the country, though in a less degree than during
the day, as the clouds will remit towards the earth no inconsiderable
quantity of heat. But on a clear night, in an open part of the country, nothing
almost can be returned to us from above in place of the heat which we
radiate upward. In towns, however, some compensation will be afforded
even on the clearest nights for the heat which we lose in the open air by that
which is radiated to us from the sun round buildings.
"To our loss of heat by radiation at times that we derive little
compensation from the radiation of other bodies is probably to be attributed
a great part of the hurtful effects of the night air. Descartes says that these

are not owing to dew, as was the common opinion of his contemporaries,
but to the descent of certain noxious vapors which have been exhaled from
the earth during the heat of the day, and are afterwards condensed by the
cold of a serene night. The effects in question certainly cannot be
occasioned by dew, since that fluid does not form upon a healthy human
body in temperate climates; but they may, notwithstanding, arise from the
same cause that produces dew on those substances which do not, like the
human body, possess the power of generating heat for the supply of what
they lose by radiation or any other means."(2)
This explanation made it plain why dew forms on a clear night, when
there are no clouds to reflect the radiant heat. Combined with Dalton's
theory that vapor is an independent gas, limited in quantity in any given
space by the temperature of that space, it solved the problem of the
formation of clouds, rain, snow, and hoar-frost. Thus this paper of Wells's
closed the epoch of speculation regarding this field of meteorology, as
Hutton's paper of 1784 had opened it. The fact that the volume containing
Hutton's paper contained also his epoch-making paper on geology finds
curiously a duplication in the fact that Wells's volume contained also his
essay on Albinism, in which the doctrine of natural selection was for the
first time formulated, as Charles Darwin freely admitted after his own
efforts had made the doctrine famous.
ISOTHERMS AND OCEAN CURRENTS
The very next year after Dr. Wells's paper was published there appeared
in France the third volume of the Memoires de Physique et de Chimie de la
Societe d'Arcueil, and a new epoch in meteorology was inaugurated. The
society in question was numerically an inconsequential band, listing only a
dozen members; but every name was a famous one: Arago, Berard,
Berthollet, Biot, Chaptal, De Candolle, Dulong, Gay-Lussac, Humboldt,
Laplace, Poisson, and Thenard—rare spirits every one. Little danger that
the memoirs of such a band would be relegated to the dusty shelves where
most proceedings of societies belong—no milk-for-babes fare would be
served to such a company.
The particular paper which here interests us closes this third and last
volume of memoirs. It is entitled "Des Lignes Isothermes et de la
Distribution de la Chaleursurle Globe." The author is Alexander Humboldt.
Needless to say, the topic is handled in a masterly manner. The distribution

of heat on the surface of the globe, on the mountain-sides, in the interior of
the earth; the causes that regulate such distribution; the climatic results—
these are the topics discussed. But what gives epochal character to the paper
is the introduction of those isothermal lines circling the earth in irregular
course, joining together places having the same mean annual temperature,
and thus laying the foundation for a science of comparative climatology.
It is true the attempt to study climates comparatively was not new.
Mairan had attempted it in those papers in which he developed his bizarre
ideas as to central emanations of heat. Euler had brought his profound
mathematical genius to bear on the topic, evolving the "extraordinary
conclusion that under the equator at midnight the cold ought to be more
rigorous than at the poles in winter." And in particular Richard Kirwan, the
English chemist, had combined the mathematical and the empirical methods
and calculated temperatures for all latitudes. But Humboldt differs from all
these predecessors in that he grasps the idea that the basis of all such
computations should be not theory, but fact. He drew his isothermal lines
not where some occult calculation would locate them on an ideal globe, but
where practical tests with the thermometer locate them on our globe as it is.
London, for example, lies in the same latitude as the southern extremity of
Hudson Bay; but the isotherm of London, as Humboldt outlines it, passes
through Cincinnati.
Of course such deviations of climatic conditions between places in the
same latitude had long been known. As Humboldt himself observes, the
earliest settlers of America were astonished to find themselves subjected to
rigors of climate for which their European experience had not at all
prepared them. Moreover, sagacious travellers, in particular Cook's
companion on his second voyage, young George Forster, had noted as a
general principle that the western borders of continents in temperate regions
are always warmer than corresponding latitudes of their eastern borders;
and of course the general truth of temperatures being milder in the vicinity
of the sea than in the interior of continents had long been familiar. But
Humboldt's isothermal lines for the first time gave tangibility to these ideas,
and made practicable a truly scientific study of comparative climatology.
In studying these lines, particularly as elaborated by further observations,
it became clear that they are by no means haphazard in arrangement, but are
dependent upon geographical conditions which in most cases are not

difficult to determine. Humboldt himself pointed out very clearly the main
causes that tend to produce deviations from the average—or, as Dove later
on called it, the normal—temperature of any given latitude. For example,
the mean annual temperature of a region (referring mainly to the northern
hemisphere) is raised by the proximity of a western coast; by a divided
configuration of the continent into peninsulas; by the existence of open seas
to the north or of radiating continental surfaces to the south; by mountain
ranges to shield from cold winds; by the infrequency of swamps to become
congealed; by the absence of woods in a dry, sandy soil; and by the serenity
of sky in the summer months and the vicinity of an ocean current bringing
water which is of a higher temperature than that of the surrounding sea.
Conditions opposite to these tend, of course, correspondingly to lower
the temperature. In a word, Humboldt says the climatic distribution of heat
depends on the relative distribution of land and sea, and on the
"hypsometrical configuration of the continents"; and he urges that "great
meteorological phenomena cannot be comprehended when considered
independently of geognostic relations"—a truth which, like most other
general principles, seems simple enough once it is pointed out.
With that broad sweep of imagination which characterized him,
Humboldt speaks of the atmosphere as the "aerial ocean, in the lower strata
and on the shoals of which we live," and he studies the atmospheric
phenomena always in relation to those of that other ocean of water. In each
of these oceans there are vast permanent currents, flowing always in
determinate directions, which enormously modify the climatic conditions of
every zone. The ocean of air is a vast maelstrom, boiling up always under
the influence of the sun's heat at the equator, and flowing as an upper
current towards either pole, while an undercurrent from the poles, which
becomes the trade-winds, flows towards the equator to supply its place.
But the superheated equatorial air, becoming chilled, descends to the
surface in temperate latitudes, and continues its poleward journey as the
anti-trade-winds. The trade-winds are deflected towards the west, because
in approaching the equator they constantly pass over surfaces of the earth
having a greater and greater velocity of rotation, and so, as it were, tend to
lag behind—an explanation which Hadley pointed out in 1735, but which
was not accepted until Dalton independently worked it out and promulgated
it in 1793. For the opposite reason, the anti-trades are deflected towards the

east; hence it is that the western, borders of continents in temperate zones
are bathed in moist sea-breezes, while their eastern borders lack this cold-
dispelling influence.
In the ocean of water the main currents run as more sharply
circumscribed streams—veritable rivers in the sea. Of these the best known
and most sharply circumscribed is the familiar Gulf Stream, which has its
origin in an equatorial current, impelled westward by trade-winds, which is
deflected northward in the main at Cape St. Roque, entering the Caribbean
Sea and Gulf of Mexico, to emerge finally through the Strait of Florida, and
journey off across the Atlantic to warm the shores of Europe.
Such, at least, is the Gulf Stream as Humboldt understood it. Since his
time, however, ocean currents in general, and this one in particular, have
been the subject of no end of controversy, it being hotly disputed whether
either causes or effects of the Gulf Stream are just what Humboldt, in
common with others of his time, conceived them to be. About the middle of
the century Lieutenant M. F. Maury, the distinguished American
hydrographer and meteorologist, advocated a theory of gravitation as the
chief cause of the currents, claiming that difference in density, due to
difference in temperature and saltness, would sufficiently account for the
oceanic circulation. This theory gained great popularity through the wide
circulation of Maury's Physical Geography of the Sea, which is said to have
passed through more editions than any other scientific book of the period;
but it was ably and vigorously combated by Dr. James Croll, the Scottish
geologist, in his Climate and Time, and latterly the old theory that ocean
currents are due to the trade-winds has again come into favor. Indeed, very
recently a model has been constructed, with the aid of which it is said to
have been demonstrated that prevailing winds in the direction of the actual
trade-winds would produce such a current as the Gulf Stream.
Meantime, however, it is by no means sure that gravitation does not enter
into the case to the extent of producing an insensible general oceanic
circulation, independent of the Gulf Stream and similar marked currents,
and similar in its larger outlines to the polar-equatorial circulation of the air.
The idea of such oceanic circulation was first suggested in detail by
Professor Lenz, of St. Petersburg, in 1845, but it was not generally
recognized until Dr. Carpenter independently hit upon the idea more than
twenty years later. The plausibility of the conception is obvious; yet the

alleged fact of such circulation has been hotly disputed, and the question is
still sub judice.
But whether or not such general circulation of ocean water takes place, it
is beyond dispute that the recognized currents carry an enormous quantity
of heat from the tropics towards the poles. Dr. Croll, who has perhaps given
more attention to the physics of the subject than almost any other person,
computes that the Gulf Stream conveys to the North Atlantic one-fourth as
much heat as that body receives directly from the sun, and he argues that
were it not for the transportation of heat by this and similar Pacific currents,
only a narrow tropical region of the globe would be warm enough for
habitation by the existing faunas. Dr. Croll argues that a slight change in the
relative values of northern and southern trade-winds (such as he believes
has taken place at various periods in the past) would suffice to so alter the
equatorial current which now feeds the Gulf Stream that its main bulk
would be deflected southward instead of northward, by the angle of Cape
St. Roque. Thus the Gulf Stream would be nipped in the bud, and,
according to Dr. Croll's estimates, the results would be disastrous for the
northern hemisphere. The anti-trades, which now are warmed by the Gulf
Stream, would then blow as cold winds across the shores of western
Europe, and in all probability a glacial epoch would supervene throughout
the northern hemisphere.
The same consequences, so far as Europe is concerned at least, would
apparently ensue were the Isthmus of Panama to settle into the sea, allowing
the Caribbean current to pass into the Pacific. But the geologist tells us that
this isthmus rose at a comparatively recent geological period, though it is
hinted that there had been some time previously a temporary land
connection between the two continents. Are we to infer, then, that the two
Americas in their unions and disunions have juggled with the climate of the
other hemisphere? Apparently so, if the estimates made of the influence of
the Gulf Stream be tenable. It is a far cry from Panama to Russia. Yet it
seems within the possibilities that the meteorologist may learn from the
geologist of Central America something that will enable him to explain to
the paleontologist of Europe how it chanced that at one time the mammoth
and rhinoceros roamed across northern Siberia, while at another time the
reindeer and musk-ox browsed along the shores of the Mediterranean.

Possibilities, I said, not probabilities. Yet even the faint glimmer of so
alluring a possibility brings home to one with vividness the truth of
Humboldt's perspicuous observation that meteorology can be properly
comprehended only when studied in connection with the companion
sciences. There are no isolated phenomena in nature.
CYCLONES AND ANTI-CYCLONES
Yet, after all, it is not to be denied that the chief concern of the
meteorologist must be with that other medium, the "ocean of air, on the
shoals of which we live." For whatever may be accomplished by water
currents in the way of conveying heat, it is the wind currents that effect the
final distribution of that heat. As Dr. Croll has urged, the waters of the Gulf
Stream do not warm the shores of Europe by direct contact, but by warming
the anti-trade-winds, which subsequently blow across the continent. And
everywhere the heat accumulated by water becomes effectual in modifying
climate, not so much by direct radiation as by diffusion through the medium
of the air.
This very obvious importance of aerial currents led to their practical
study long before meteorology had any title to the rank of science, and
Dalton's explanation of the trade-winds had laid the foundation for a science
of wind dynamics before the beginning of the nineteenth century. But no
substantial further advance in this direction was effected until about 1827,
when Heinrich W. Dove, of Konigsberg, afterwards to be known as perhaps
the foremost meteorologist of his generation, included the winds among the
subjects of his elaborate statistical studies in climatology.
Dove classified the winds as permanent, periodical, and variable. His
great discovery was that all winds, of whatever character, and not merely
the permanent winds, come under the influence of the earth's rotation in
such a way as to be deflected from their course, and hence to take on a
gyratory motion—that, in short, all local winds are minor eddies in the great
polar-equatorial whirl, and tend to reproduce in miniature the character of
that vast maelstrom. For the first time, then, temporary or variable winds
were seen to lie within the province of law.
A generation later, Professor William Ferrel, the American meteorologist,
who had been led to take up the subject by a perusal of Maury's discourse
on ocean winds, formulated a general mathematical law, to the effect that
any body moving in a right line along the surface of the earth in any

direction tends to have its course deflected, owing to the earth's rotation, to
the right hand in the northern and to the left hand in the southern
hemisphere. This law had indeed been stated as early as 1835 by the French
physicist Poisson, but no one then thought of it as other than a mathematical
curiosity; its true significance was only understood after Professor Ferrel
had independently rediscovered it (just as Dalton rediscovered Hadley's
forgotten law of the trade-winds) and applied it to the motion of wind
currents.
Then it became clear that here is a key to the phenomena of atmospheric
circulation, from the great polar-equatorial maelstrom which manifests
itself in the trade-winds to the most circumscribed riffle which is announced
as a local storm. And the more the phenomena were studied, the more
striking seemed the parallel between the greater maelstrom and these lesser
eddies. Just as the entire atmospheric mass of each hemisphere is seen,
when viewed as a whole, to be carried in a great whirl about the pole of that
hemisphere, so the local disturbances within this great tide are found always
to take the form of whirls about a local storm-centre—which storm-centre,
meantime, is carried along in the major current, as one often sees a little
whirlpool in the water swept along with the main current of the stream.
Sometimes, indeed, the local eddy, caught as it were in an ancillary current
of the great polar stream, is deflected from its normal course and may seem
to travel against the stream; but such deviations are departures from the
rule. In the great majority of cases, for example, in the north temperate
zone, a storm-centre (with its attendant local whirl) travels to the northeast,
along the main current of the anti-trade-wind, of which it is a part; and
though exceptionally its course may be to the southeast instead, it almost
never departs so widely from the main channel as to progress to the
westward. Thus it is that storms sweeping over the United States can be
announced, as a rule, at the seaboard in advance of their coming by
telegraphic communication from the interior, while similar storms come to
Europe off the ocean unannounced. Hence the more practical availability of
the forecasts of weather bureaus in the former country.
But these local whirls, it must be understood, are local only in a very
general sense of the word, inasmuch as a single one may be more than a
thousand miles in diameter, and a small one is two or three hundred miles
across. But quite without regard to the size of the whirl, the air composing it
conducts itself always in one of two ways. It never whirls in concentric

circles; it always either rushes in towards the centre in a descending spiral,
in which case it is called a cyclone, or it spreads out from the centre in a
widening spiral, in which case it is called an anti-cyclone. The word
cyclone is associated in popular phraseology with a terrific storm, but it has
no such restriction in technical usage. A gentle zephyr flowing towards a
"storm-centre" is just as much a cyclone to the meteorologist as is the whirl
constituting a West-Indian hurricane. Indeed, it is not properly the wind
itself that is called the cyclone in either case, but the entire system of whirls
—including the storm-centre itself, where there may be no wind at all.
What, then, is this storm-centre? Merely an area of low barometric
pressure—an area where the air has become lighter than the air of
surrounding regions. Under influence of gravitation the air seeks its level
just as water does; so the heavy air comes flowing in from all sides towards
the low-pressure area, which thus becomes a "storm-centre." But the
inrushing currents never come straight to their mark. In accordance with
Ferrel's law, they are deflected to the right, and the result, as will readily be
seen, must be a vortex current, which whirls always in one direction—
namely, from left to right, or in the direction opposite to that of the hands of
a watch held with its face upward. The velocity of the cyclonic currents will
depend largely upon the difference in barometric pressure between the
storm-centre and the confines of the cyclone system. And the velocity of the
currents will determine to some extent the degree of deflection, and hence
the exact path of the descending spiral in which the wind approaches the
centre. But in every case and in every part of the cyclone system it is true,
as Buys Ballot's famous rule first pointed out, that a person standing with
his back to the wind has the storm-centre at his left.
The primary cause of the low barometric pressure which marks the
storm-centre and establishes the cyclone is expansion of the air through
excess of temperature. The heated air, rising into cold upper regions, has a
portion of its vapor condensed into clouds, and now a new dynamic factor
is added, for each particle of vapor, in condensing, gives up its modicum of
latent heat. Each pound of vapor thus liberates, according to Professor
Tyndall's estimate, enough heat to melt five pounds of cast iron; so the
amount given out where large masses of cloud are forming must
enormously add to the convection currents of the air, and hence to the
storm-developing power of the forming cyclone. Indeed, one school of
meteorologists, of whom Professor Espy was the leader, has held that,

without such added increment of energy constantly augmenting the
dynamic effects, no storm could long continue in violent action. And it is
doubted whether any storm could ever attain, much less continue, the
terrific force of that most dreaded of winds of temperate zones, the tornado
—a storm which obeys all the laws of cyclones, but differs from ordinary
cyclones in having a vortex core only a few feet or yards in diameter—
without the aid of those great masses of condensing vapor which always
accompany it in the form of storm-clouds.
The anti-cyclone simply reverses the conditions of the cyclone. Its centre
is an area of high pressure, and the air rushes out from it in all directions
towards surrounding regions of low pressure. As before, all parts of the
current will be deflected towards the right, and the result, clearly, is a whirl
opposite in direction to that of the cyclone. But here there is a tendency to
dissipation rather than to concentration of energy, hence, considered as a
storm-generator, the anti-cyclone is of relative insignificance.
In particular the professional meteorologist who conducts a "weather
bureau"—as, for example, the chief of the United States signal-service
station in New York—is so preoccupied with the observation of this
phenomenon that cyclone-hunting might be said to be his chief pursuit. It is
for this purpose, in the main, that government weather bureaus or signal-
service departments have been established all over the world. Their chief
work is to follow up cyclones, with the aid of telegraphic reports, mapping
their course and recording the attendant meteorological conditions. Their
so-called predictions or forecasts are essentially predications, gaining
locally the effect of predictions because the telegraph outstrips the wind.
At only one place on the globe has it been possible as yet for the
meteorologist to make long-time forecasts meriting the title of predictions.
This is in the middle Ganges Valley of northern India. In this country the
climatic conditions are largely dependent upon the periodical winds called
monsoons, which blow steadily landward from April to October, and
seaward from October to April. The summer monsoons bring the all-
essential rains; if they are delayed or restricted in extent, there will be
drought and consequent famine. And such restriction of the monsoon is
likely to result when there has been an unusually deep or very late snowfall
on the Himalayas, because of the lowering of spring temperature by the
melting snow. Thus here it is possible, by observing the snowfall in the

mountains, to predict with some measure of success the average rainfall of
the following summer. The drought of 1896, with the consequent famine
and plague that devastated India the following winter, was thus predicted
some months in advance.
This is the greatest present triumph of practical meteorology. Nothing
like it is yet possible anywhere in temperate zones. But no one can say what
may not be possible in times to come, when the data now being gathered all
over the world shall at last be co-ordinated, classified, and made the basis of
broad inductions. Meteorology is pre-eminently a science of the future.

VI. MODERN THEORIES OF HEAT AND
LIGHT
THE eighteenth-century philosopher made great strides in his studies of
the physical properties of matter and the application of these properties in
mechanics, as the steam-engine, the balloon, the optic telegraph, the
spinning-jenny, the cotton-gin, the chronometer, the perfected compass, the
Leyden jar, the lightning-rod, and a host of minor inventions testify. In a
speculative way he had thought out more or less tenable conceptions as to
the ultimate nature of matter, as witness the theories of Leibnitz and
Boscovich and Davy, to which we may recur. But he had not as yet
conceived the notion of a distinction between matter and energy, which is
so fundamental to the physics of a later epoch. He did not speak of heat,
light, electricity, as forms of energy or "force"; he conceived them as subtile
forms of matter—as highly attenuated yet tangible fluids, subject to
gravitation and chemical attraction; though he had learned to measure none
of them but heat with accuracy, and this one he could test only within
narrow limits until late in the century, when Josiah Wedgwood, the famous
potter, taught him to gauge the highest temperatures with the clay
pyrometer.
He spoke of the matter of heat as being the most universally distributed
fluid in nature; as entering in some degree into the composition of nearly all
other substances; as being sometimes liquid, sometimes condensed or solid,
and as having weight that could be detected with the balance. Following
Newton, he spoke of light as a "corpuscular emanation" or fluid, composed
of shining particles which possibly are transmutable into particles of heat,
and which enter into chemical combination with the particles of other forms
of matter. Electricity he considered a still more subtile kind of matter-
perhaps an attenuated form of light. Magnetism, "vital fluid," and by some
even a "gravic fluid," and a fluid of sound were placed in the same scale;
and, taken together, all these supposed subtile forms of matter were classed
as "imponderables."

This view of the nature of the "imponderables" was in some measure a
retrogression, for many seventeenth-century philosophers, notably Hooke
and Huygens and Boyle, had held more correct views; but the materialistic
conception accorded so well with the eighteenth-century tendencies of
thought that only here and there a philosopher like Euler called it in
question, until well on towards the close of the century. Current speech
referred to the materiality of the "imponderables" unquestioningly. Students
of meteorology—a science that was just dawning—explained atmospheric
phenomena on the supposition that heat, the heaviest imponderable,
predominated in the lower atmosphere, and that light, electricity, and
magnetism prevailed in successively higher strata. And Lavoisier, the most
philosophical chemist of the century, retained heat and light on a par with
oxygen, hydrogen, iron, and the rest, in his list of elementary substances.
COUNT RUMFORD AND THE VIBRATORY THEORY OF HEAT
But just at the close of the century the confidence in the status of the
imponderables was rudely shaken in the minds of philosophers by the
revival of the old idea of Fra Paolo and Bacon and Boyle, that heat, at any
rate, is not a material fluid, but merely a mode of motion or vibration
among the particles of "ponderable" matter. The new champion of the old
doctrine as to the nature of heat was a very distinguished philosopher and
diplomatist of the time, who, it may be worth recalling, was an American.
He was a sadly expatriated American, it is true, as his name, given all the
official appendages, will amply testify; but he had been born and reared in a
Massachusetts village none the less, and he seems always to have retained a
kindly interest in the land of his nativity, even though he lived abroad in the
service of other powers during all the later years of his life, and was
knighted by England, ennobled by Bavaria, and honored by the most
distinguished scientific bodies of Europe. The American, then, who
championed the vibratory theory of heat, in opposition to all current
opinion, in this closing era of the eighteenth century, was Lieutenant-
General Sir Benjamin Thompson, Count Rumford, F.R.S.
Rumford showed that heat may be produced in indefinite quantities by
friction of bodies that do not themselves lose any appreciable matter in the
process, and claimed that this proves the immateriality of heat. Later on he
added force to the argument by proving, in refutation of the experiments of
Bowditch, that no body either gains or loses weight in virtue of being

heated or cooled. He thought he had proved that heat is only a form of
motion.
His experiment for producing indefinite quantities of heat by friction is
recorded by him in his paper entitled, "Inquiry Concerning the Source of
Heat Excited by Friction."
"Being engaged, lately, in superintending the boring of cannon in the
workshops of the military arsenal at Munich," he says, "I was struck with
the very considerable degree of heat which a brass gun acquires in a short
time in being bored; and with the still more intense heat (much greater than
that of boiling water, as I found by experiment) of the metallic chips
separated from it by the borer.
"Taking a cannon (a brass six-pounder), cast solid, and rough, as it came
from the foundry, and fixing it horizontally in a machine used for boring,
and at the same time finishing the outside of the cannon by turning, I caused
its extremity to be cut off; and by turning down the metal in that part, a
solid cylinder was formed, 7 3/4 inches in diameter and 9 8/10 inches long;
which, when finished, remained joined to the rest of the metal (that which,
properly speaking, constituted the cannon) by a small cylindrical neck, only
2 1/5 inches in diameter and 3 8/10 inches long.
"This short cylinder, which was supported in its horizontal position, and
turned round its axis by means of the neck by which it remained united to
the cannon, was now bored with the horizontal borer used in boring cannon.
"This cylinder being designed for the express purpose of generating heat
by friction, by having a blunt borer forced against its solid bottom at the
same time that it should be turned round its axis by the force of horses, in
order that the heat accumulated in the cylinder might from time to time be
measured, a small, round hole 0.37 of an inch only in diameter and 4.2
inches in depth, for the purpose of introducing a small cylindrical mercurial
thermometer, was made in it, on one side, in a direction perpendicular to the
axis of the cylinder, and ending in the middle of the solid part of the metal
which formed the bottom of the bore.
"At the beginning of the experiment, the temperature of the air in the
shade, as also in the cylinder, was just sixty degrees Fahrenheit. At the end
of thirty minutes, when the cylinder had made 960 revolutions about its
axis, the horses being stopped, a cylindrical mercury thermometer, whose
bulb was 32/100 of an inch in diameter and 3 1/4 inches in length, was

introduced into the hole made to receive it in the side of the cylinder, when
the mercury rose almost instantly to one hundred and thirty degrees.
"In order, by one decisive experiment, to determine whether the air of the
atmosphere had any part or not in the generation of the heat, I contrived to
repeat the experiment under circumstances in which it was evidently
impossible for it to produce any effect whatever. By means of a piston
exactly fitted to the mouth of the bore of the cylinder, through the middle of
which piston the square iron bar, to the end of which the blunt steel borer
was fixed, passed in a square hole made perfectly air-tight, the excess of the
external air, to the inside of the bore of the cylinder, was effectually
prevented. I did not find, however, by this experiment that the exclusion of
the air diminished in the smallest degree the quantity of heat excited by the
friction.
"There still remained one doubt, which, though it appeared to me to be so
slight as hardly to deserve any attention, I was, however, desirous to
remove. The piston which choked the mouth of the bore of the cylinder, in
order that it might be air-tight, was fitted into it with so much nicety, by
means of its collars of leather, and pressed against it with so much force,
that, notwithstanding its being oiled, it occasioned a considerable degree of
friction when the hollow cylinder was turned round its axis. Was not the
heat produced, or at least some part of it, occasioned by this friction of the
piston? and, as the external air had free access to the extremity of the bore,
where it came into contact with the piston, is it not possible that this air may
have had some share in the generation of the heat produced?
"A quadrangular oblong deal box, water-tight, being provided with holes
or slits in the middle of each of its ends, just large enough to receive, the
one the square iron rod to the end of which the blunt steel borer was
fastened, the other the small cylindrical neck which joined the hollow
cylinder to the cannon; when this box (which was occasionally closed
above by a wooden cover or lid moving on hinges) was put into its place—
that is to say, when, by means of the two vertical opening or slits in its two
ends, the box was fixed to the machinery in such a manner that its bottom
being in the plane of the horizon, its axis coincided with the axis of the
hollow metallic cylinder, it is evident, from the description, that the hollow,
metallic cylinder would occupy the middle of the box, without touching it
on either side; and that, on pouring water into the box and filling it to the

brim, the cylinder would be completely covered and surrounded on every
side by that fluid. And, further, as the box was held fast by the strong,
square iron rod which passed in a square hole in the centre of one of its
ends, while the round or cylindrical neck which joined the hollow cylinder
to the end of the cannon could turn round freely on its axis in the round hole
in the centre of the other end of it, it is evident that the machinery could be
put in motion without the least danger of forcing the box out of its place,
throwing the water out of it, or deranging any part of the apparatus."
Everything being thus ready, the box was filled with cold water, having
been made water-tight by means of leather collars, and the machinery put in
motion. "The result of this beautiful experiment," says Rumford, "was very
striking, and the pleasure it afforded me amply repaid me for all the trouble
I had had in contriving and arranging the complicated machinery used in
making it. The cylinder, revolving at the rate of thirty-two times in a
minute, had been in motion but a short time when I perceived, by putting
my hand into the water and touching the outside of the cylinder, that heat
was generated, and it was not long before the water which surrounded the
cylinder began to be sensibly warm.
"At the end of one hour I found, by plunging a thermometer into the
box,... that its temperature had been raised no less than forty-seven degrees
Fahrenheit, being now one hundred and seven degrees Fahrenheit. ... One
hour and thirty minutes after the machinery had been put in motion the heat
of the water in the box was one hundred and forty-two degrees. At the end
of two hours... it was raised to one hundred and seventy-eight degrees; and
at two hours and thirty minutes it ACTUALLY BOILED!
"It would be difficult to describe the surprise and astonishment expressed
in the countenances of the bystanders on seeing so large a quantity of cold
water heated, and actually made to boil, without any fire. Though there was,
in fact, nothing that could justly be considered as a surprise in this event,
yet I acknowledge fairly that it afforded me a degree of childish pleasure
which, were I ambitious of the reputation of a GRAVE PHILOSOPHER, I
ought most certainly rather to hide than to discover...."
Having thus dwelt in detail on these experiments, Rumford comes now to
the all-important discussion as to the significance of them—the subject that
had been the source of so much speculation among the philosophers—the

question as to what heat really is, and if there really is any such thing (as
many believed) as an igneous fluid, or a something called caloric.
"From whence came this heat which was continually given off in this
manner, in the foregoing experiments?" asks Rumford. "Was it furnished by
the small particles of metal detached from the larger solid masses on their
being rubbed together? This, as we have already seen, could not possibly
have been the case.
"Was it furnished by the air? This could not have been the case; for, in
three of the experiments, the machinery being kept immersed in water, the
access of the air of the atmosphere was completely prevented.
"Was it furnished by the water which surrounded the machinery? That
this could not have been the case is evident: first, because this water was
continually RECEIVING heat from the machinery, and could not, at the
same time, be GIVING TO and RECEIVING HEAT FROM the same body;
and, secondly, because there was no chemical decomposition of any part of
this water. Had any such decomposition taken place (which, indeed, could
not reasonably have been expected), one of its component elastic fluids
(most probably hydrogen) must, at the same time, have been set at liberty,
and, in making its escape into the atmosphere, would have been detected;
but, though I frequently examined the water to see if any air-bubbles rose
up through it, and had even made preparations for catching them if they
should appear, I could perceive none; nor was there any sign of
decomposition of any kind whatever, or other chemical process, going on in
the water.
"Is it possible that the heat could have been supplied by means of the iron
bar to the end of which the blunt steel borer was fixed? Or by the small
neck of gun-metal by which the hollow cylinder was united to the cannon?
These suppositions seem more improbable even than either of the before-
mentioned; for heat was continually going off, or OUT OF THE
MACHINERY, by both these passages during the whole time the
experiment lasted.
"And in reasoning on this subject we must not forget to consider that
most remarkable circumstance, that the source of the heat generated by
friction in these experiments appeared evidently to be INEXHAUSTIBLE.
"It is hardly necessary to add that anything which any INSULATED
body, or system of bodies, can continue to furnish WITHOUT

LIMITATION cannot possibly be a MATERIAL substance; and it appears
to me to be extremely difficult, if not quite impossible, to form any distinct
idea of anything capable of being excited and communicated, in the manner
the heat was excited and communicated in these experiments, except in
MOTION."(1)
THOMAS YOUNG AND THE WAVE THEORY OF LIGHT
But contemporary judgment, while it listened respectfully to Rumford,
was little minded to accept his verdict. The cherished beliefs of a generation
are not to be put down with a single blow. Where many minds have a
similar drift, however, the first blow may precipitate a general conflict; and
so it was here. Young Humphry Davy had duplicated Rumford's
experiments, and reached similar conclusions; and soon others fell into line.
Then, in 1800, Dr. Thomas Young—"Phenomenon Young" they called him
at Cambridge, because he was reputed to know everything—took up the
cudgels for the vibratory theory of light, and it began to be clear that the
two "imponderables," heat and light, must stand or fall together; but no one
as yet made a claim against the fluidity of electricity.
Before we take up the details of the assault made by Young upon the old
doctrine of the materiality of light, we must pause to consider the
personality of Young himself. For it chanced that this Quaker physician was
one of those prodigies who come but few times in a century, and the full list
of whom in the records of history could be told on one's thumbs and
fingers. His biographers tell us things about him that read like the most
patent fairy-tales. As a mere infant in arms he had been able to read fluently.
Before his fourth birthday came he had read the Bible twice through, as
well as Watts's Hymns—poor child!—and when seven or eight he had
shown a propensity to absorb languages much as other children absorb
nursery tattle and Mother Goose rhymes. When he was fourteen, a young
lady visiting the household of his tutor patronized the pretty boy by asking
to see a specimen of his penmanship. The pretty boy complied readily
enough, and mildly rebuked his interrogator by rapidly writing some
sentences for her in fourteen languages, including such as, Arabian, Persian,
and Ethiopic.
Meantime languages had been but an incident in the education of the lad.
He seems to have entered every available field of thought—mathematics,
physics, botany, literature, music, painting, languages, philosophy,

archaeology, and so on to tiresome lengths—and once he had entered any
field he seldom turned aside until he had reached the confines of the subject
as then known and added something new from the recesses of his own
genius. He was as versatile as Priestley, as profound as Newton himself. He
had the range of a mere dilettante, but everywhere the full grasp of the
master. He took early for his motto the saying that what one man has done,
another man may do. Granting that the other man has the brain of a Thomas
Young, it is a true motto.
Such, then, was the young Quaker who came to London to follow out the
humdrum life of a practitioner of medicine in the year 1801. But
incidentally the young physician was prevailed upon to occupy the interims
of early practice by fulfilling the duties of the chair of Natural Philosophy at
the Royal Institution, which Count Rumford had founded, and of which
Davy was then Professor of Chemistry—the institution whose glories have
been perpetuated by such names as Faraday and Tyndall, and which the
Briton of to-day speaks of as the "Pantheon of Science." Here it was that
Thomas Young made those studies which have insured him a niche in the
temple of fame not far removed from that of Isaac Newton.
As early as 1793, when he was only twenty, Young had begun to
Communicate papers to the Royal Society of London, which were adjudged
worthy to be printed in full in the Philosophical Transactions; so it is not
strange that he should have been asked to deliver the Bakerian lecture
before that learned body the very first year after he came to London. The
lecture was delivered November 12, 1801. Its subject was "The Theory of
Light and Colors," and its reading marks an epoch in physical science; for
here was brought forward for the first time convincing proof of that
undulatory theory of light with which every student of modern physics is
familiar—the theory which holds that light is not a corporeal entity, but a
mere pulsation in the substance of an all-pervading ether, just as sound is a
pulsation in the air, or in liquids or solids.
Young had, indeed, advocated this theory at an earlier date, but it was not
until 1801 that he hit upon the idea which enabled him to bring it to
anything approaching a demonstration. It was while pondering over the
familiar but puzzling phenomena of colored rings into which white light is
broken when reflected from thin films—Newton's rings, so called—that an
explanation occurred to him which at once put the entire undulatory theory

on a new footing. With that sagacity of insight which we call genius, he saw
of a sudden that the phenomena could be explained by supposing that when
rays of light fall on a thin glass, part of the rays being reflected from the
upper surface, other rays, reflected from the lower surface, might be so
retarded in their course through the glass that the two sets would interfere
with one another, the forward pulsation of one ray corresponding to the
backward pulsation of another, thus quite neutralizing the effect. Some of
the component pulsations of the light being thus effaced by mutual
interference, the remaining rays would no longer give the optical effect of
white light; hence the puzzling colors.
Here is Young's exposition of the subject:
Of the Colors of Thin Plates
"When a beam of light falls upon two refracting surfaces, the partial
reflections coincide perfectly in direction; and in this case the interval of
retardation taken between the surfaces is to their radius as twice the cosine
of the angle of refraction to the radius.
"Let the medium between the surfaces be rarer than the surrounding
mediums; then the impulse reflected at the second surface, meeting a
subsequent undulation at the first, will render the particles of the rarer
medium capable of wholly stopping the motion of the denser and destroying
the reflection, while they themselves will be more strongly propelled than if
they had been at rest, and the transmitted light will be increased. So that the
colors by reflection will be destroyed, and those by transmission rendered
more vivid, when the double thickness or intervals of retardation are any
multiples of the whole breadth of the undulations; and at intermediate
thicknesses the effects will be reversed according to the Newtonian
observation.
"If the same proportions be found to hold good with respect to thin plates
of a denser medium, which is, indeed, not improbable, it will be necessary
to adopt the connected demonstrations of Prop. IV., but, at any rate, if a thin
plate be interposed between a rarer and a denser medium, the colors by
reflection and transmission may be expected to change places."
OF THE COLORS OF THICK PLATES
"When a beam of light passes through a refracting surface, especially if
imperfectly polished, a portion of it is irregularly scattered, and makes the
surface visible in all directions, but most conspicuously in directions not far

distant from that of the light itself; and if a reflecting surface be placed
parallel to the refracting surface, this scattered light, as well as the principal
beam, will be reflected, and there will be also a new dissipation of light, at
the return of the beam through the refracting surface. These two portions of
scattered light will coincide in direction; and if the surfaces be of such a
form as to collect the similar effects, will exhibit rings of colors. The
interval of retardation is here the difference between the paths of the
principal beam and of the scattered light between the two surfaces; of
course, wherever the inclination of the scattered light is equal to that of the
beam, although in different planes, the interval will vanish and all the
undulations will conspire. At other inclinations, the interval will be the
difference of the secants from the secant of the inclination, or angle of
refraction of the principal beam. From these causes, all the colors of
concave mirrors observed by Newton and others are necessary
consequences; and it appears that their production, though somewhat
similar, is by no means as Newton imagined, identical with the production
of thin plates."(2)
By following up this clew with mathematical precision, measuring the
exact thickness of the plate and the space between the different rings of
color, Young was able to show mathematically what must be the length of
pulsation for each of the different colors of the spectrum. He estimated that
the undulations of red light, at the extreme lower end of the visible
spectrum, must number about thirty-seven thousand six hundred and forty
to the inch, and pass any given spot at a rate of four hundred and sixty-three
millions of millions of undulations in a second, while the extreme violet
numbers fifty-nine thousand seven hundred and fifty undulations to the
inch, or seven hundred and thirty-five millions of millions to the second.
The Colors of Striated Surfaces
Young similarly examined the colors that are produced by scratches on a
smooth surface, in particular testing the light from "Mr. Coventry's
exquisite micrometers," which consist of lines scratched on glass at
measured intervals. These microscopic tests brought the same results as the
other experiments. The colors were produced at certain definite and
measurable angles, and the theory of interference of undulations explained
them perfectly, while, as Young affirmed with confidence, no other
hypothesis hitherto advanced would explain them at all. Here are his words:

"Let there be in a given plane two reflecting points very near each other,
and let the plane be so situated that the reflected image of a luminous object
seen in it may appear to coincide with the points; then it is obvious that the
length of the incident and reflected ray, taken together, is equal with respect
to both points, considering them as capable of reflecting in all directions.
Let one of the points be now depressed below the given plane; then the
whole path of the light reflected from it will be lengthened by a line which
is to the depression of the point as twice the cosine of incidence to the
radius.
"If, therefore, equal undulations of given dimensions be reflected from
two points, situated near enough to appear to the eye but as one, whenever
this line is equal to half the breadth of a whole undulation the reflection
from the depressed point will so interfere with the reflection from the fixed
point that the progressive motion of the one will coincide with the
retrograde motion of the other, and they will both be destroyed; but when
this line is equal to the whole breadth of an undulation, the effect will be
doubled, and when to a breadth and a half, again destroyed; and thus for a
considerable number of alternations, and if the reflected undulations be of a
different kind, they will be variously affected, according to their proportions
to the various length of the line which is the difference between the lengths
of their two paths, and which may be denominated the interval of a
retardation.
"In order that the effect may be the more perceptible, a number of pairs
of points must be united into two parallel lines; and if several such pairs of
lines be placed near each other, they will facilitate the observation. If one of
the lines be made to revolve round the other as an axis, the depression
below the given plane will be as the sine of the inclination; and while the
eye and the luminous object remain fixed the difference of the length of the
paths will vary as this sine.
"The best subjects for the experiment are Mr. Coventry's exquisite
micrometers; such of them as consist of parallel lines drawn on glass, at a
distance of one-five-hundredth of an inch, are the most convenient. Each of
these lines appears under a microscope to consist of two or more finer lines,
exactly parallel, and at a distance of somewhat more than a twentieth more
than the adjacent lines. I placed one of these so as to reflect the sun's light at
an angle of forty-five degrees, and fixed it in such a manner that while it

revolved round one of the lines as an axis, I could measure its angular
motion; I found that the longest red color occurred at the inclination 10 1/4
degrees, 20 3/4 degrees, 32 degrees, and 45 degrees; of which the sines are
as the numbers 1, 2, 3, and 4. At all other angles also, when the sun's light
was reflected from the surface, the color vanished with the inclination, and
was equal at equal inclinations on either side.
This experiment affords a very strong confirmation of the theory. It is
impossible to deduce any explanation of it from any hypothesis hitherto
advanced; and I believe it would be difficult to invent any other that would
account for it. There is a striking analogy between this separation of colors
and the production of a musical note by successive echoes from equidistant
iron palisades, which I have found to correspond pretty accurately with the
known velocity of sound and the distances of the surfaces.
"It is not improbable that the colors of the integuments of some insects,
and of some other natural bodies, exhibiting in different lights the most
beautiful versatility, may be found to be of this description, and not to be
derived from thin plates. In some cases a single scratch or furrow may
produce similar effects, by the reflection of its opposite edges."(3)
This doctrine of interference of undulations was the absolutely novel part
of Young's theory. The all-compassing genius of Robert Hooke had, indeed,
very nearly apprehended it more than a century before, as Young himself
points out, but no one else bad so much as vaguely conceived it; and even
with the sagacious Hooke it was only a happy guess, never distinctly
outlined in his own mind, and utterly ignored by all others. Young did not
know of Hooke's guess until he himself had fully formulated the theory, but
he hastened then to give his predecessor all the credit that could possibly be
adjudged his due by the most disinterested observer. To Hooke's
contemporary, Huygens, who was the originator of the general doctrine of
undulation as the explanation of light, Young renders full justice also. For
himself he claims only the merit of having demonstrated the theory which
these and a few others of his predecessors had advocated without full proof.
The following year Dr. Young detailed before the Royal Society other
experiments, which threw additional light on the doctrine of interference;
and in 1803 he cited still others, which, he affirmed, brought the doctrine to
complete demonstration. In applying this demonstration to the general
theory of light, he made the striking suggestion that "the luminiferous ether

pervades the substance of all material bodies with little or no resistance, as
freely, perhaps, as the wind passes through a grove of trees." He asserted his
belief also that the chemical rays which Ritter had discovered beyond the
violet end of the visible spectrum are but still more rapid undulations of the
same character as those which produce light. In his earlier lecture he had
affirmed a like affinity between the light rays and the rays of radiant heat
which Herschel detected below the red end of the spectrum, suggesting that
"light differs from heat only in the frequency of its undulations or vibrations
—those undulations which are within certain limits with respect to
frequency affecting the optic nerve and constituting light, and those which
are slower and probably stronger constituting heat only." From the very
outset he had recognized the affinity between sound and light; indeed, it had
been this affinity that led him on to an appreciation of the undulatory theory
of light.
But while all these affinities seemed so clear to the great co-ordinating
brain of Young, they made no such impression on the minds of his
contemporaries. The immateriality of light had been substantially
demonstrated, but practically no one save its author accepted the
demonstration. Newton's doctrine of the emission of corpuscles was too
firmly rooted to be readily dislodged, and Dr. Young had too many other
interests to continue the assault unceasingly. He occasionally wrote
something touching on his theory, mostly papers contributed to the
Quarterly Review and similar periodicals, anonymously or under
pseudonym, for he had conceived the notion that too great conspicuousness
in fields outside of medicine would injure his practice as a physician. His
views regarding light (including the original papers from the Philosophical
Transactions of the Royal Society) were again given publicity in full in his
celebrated volume on natural philosophy, consisting in part of his lectures
before the Royal Institution, published in 1807; but even then they failed to
bring conviction to the philosophic world. Indeed, they did not even arouse
a controversial spirit, as his first papers had done.
ARAGO AND FRESNEL CHAMPION THE WAVE THEORY
So it chanced that when, in 1815, a young French military engineer,
named Augustin Jean Fresnel, returning from the Napoleonic wars, became
interested in the phenomena of light, and made some experiments
concerning diffraction which seemed to him to controvert the accepted

notions of the materiality of light, he was quite unaware that his
experiments had been anticipated by a philosopher across the Channel. He
communicated his experiments and results to the French Institute,
supposing them to be absolutely novel. That body referred them to a
committee, of which, as good fortune would have it, the dominating
member was Dominique Francois Arago, a man as versatile as Young
himself, and hardly less profound, if perhaps not quite so original. Arago at
once recognized the merit of Fresnel's work, and soon became a convert to
the theory. He told Fresnel that Young had anticipated him as regards the
general theory, but that much remained to be done, and he offered to
associate himself with Fresnel in prosecuting the investigation. Fresnel was
not a little dashed to learn that his original ideas had been worked out by
another while he was a lad, but he bowed gracefully to the situation and
went ahead with unabated zeal.
The championship of Arago insured the undulatory theory a hearing
before the French Institute, but by no means sufficed to bring about its
general acceptance. On the contrary, a bitter feud ensued, in which Arago
was opposed by the "Jupiter Olympus of the Academy," Laplace, by the
only less famous Poisson, and by the younger but hardly less able Biot. So
bitterly raged the feud that a life-long friendship between Arago and Biot
was ruptured forever. The opposition managed to delay the publication of
Fresnel's papers, but Arago continued to fight with his customary
enthusiasm and pertinacity, and at last, in 1823, the Academy yielded, and
voted Fresnel into its ranks, thus implicitly admitting the value of his work.
It is a humiliating thought that such controversies as this must mar the
progress of scientific truth; but fortunately the story of the introduction of
the undulatory theory has a more pleasant side. Three men, great both in
character and in intellect, were concerned in pressing its claims—Young,
Fresnel, and Arago—and the relations of these men form a picture
unmarred by any of those petty jealousies that so often dim the lustre of
great names. Fresnel freely acknowledged Young's priority so soon as his
attention was called to it; and Young applauded the work of the Frenchman,
and aided with his counsel in the application of the undulatory theory to the
problems of polarization of light, which still demanded explanation, and
which Fresnel's fertility of experimental resource and profundity of
mathematical insight sufficed in the end to conquer.

After Fresnel's admission to the Institute in 1823 the opposition
weakened, and gradually the philosophers came to realize the merits of a
theory which Young had vainly called to their attention a full quarter-
century before. Now, thanks largely to Arago, both Young and Fresnel
received their full meed of appreciation. Fresnel was given the Rumford
medal of the Royal Society of England in 1825, and chosen one of the
foreign members of the society two years later, while Young in turn was
elected one of the eight foreign members of the French Academy. As a
fitting culmination of the chapter of felicities between the three friends, it
fell to the lot of Young, as Foreign Secretary of the Royal Society, to notify
Fresnel of the honors shown him by England's representative body of
scientists; while Arago, as Perpetual Secretary of the French Institute,
conveyed to Young in the same year the notification that he had been
similarly honored by the savants of France.
A few months later Fresnel was dead, and Young survived him only two
years. Both died prematurely, but their great work was done, and the world
will remember always and link together these two names in connection with
a theory which in its implications and importance ranks little below the
theory of universal gravitation.

VII. THE MODERN DEVELOPMENT OF
ELECTRICITY AND MAGNETISM
GALVANI AND VOLTA

The full importance of Young's studies of light might perhaps have
gained earlier recognition had it not chanced that, at the time when they
were made, the attention of the philosophic world was turned with the fixity
and fascination of a hypnotic stare upon another field, which for a time
brooked no rival. How could the old, familiar phenomenon, light, interest
any one when the new agent, galvanism, was in view? As well ask one to
fix attention on a star while a meteorite blazes across the sky.
Galvanism was so called precisely as the Roentgen ray was christened at
a later day—as a safe means of begging the question as to the nature of the
phenomena involved. The initial fact in galvanism was the discovery of
Luigi Galvani (1737-1798), a physician of Bologna, in 1791, that by
bringing metals in contact with the nerves of a frog's leg violent muscular
contractions are produced. As this simple little experiment led eventually to
the discovery of galvanic electricity and the invention of the galvanic
battery, it may be regarded as the beginning of modern electricity.
The story is told that Galvani was led to his discovery while preparing
frogs' legs to make a broth for his invalid wife. As the story runs, he had
removed the skins from several frogs' legs, when, happening to touch the
exposed muscles with a scalpel which had lain in close proximity to an
electrical machine, violent muscular action was produced. Impressed with
this phenomenon, he began a series of experiments which finally resulted in
his great discovery. But be this story authentic or not, it is certain that
Galvani experimented for several years upon frogs' legs suspended upon
wires and hooks, until he finally constructed his arc of two different metals,
which, when arranged so that one was placed in contact with a nerve and
the other with a muscle, produced violent contractions.
These two pieces of metal form the basic principle of the modern
galvanic battery, and led directly to Alessandro Volta's invention of his

"voltaic pile," the immediate ancestor of the modern galvanic battery.
Volta's experiments were carried on at the same time as those of Galvani,
and his invention of his pile followed close upon Galvani's discovery of the
new form of electricity. From these facts the new form of electricity was
sometimes called "galvanic" and sometimes "voltaic" electricity, but in
recent years the term "galvanism" and "galvanic current" have almost
entirely supplanted the use of the term voltaic.
It was Volta who made the report of Galvani's wonderful discovery to the
Royal Society of London, read on January 31, 1793. In this letter he
describes Galvani's experiments in detail and refers to them in glowing
terms of praise. He calls it one of the "most beautiful and important
discoveries," and regarded it as the germ or foundation upon which other
discoveries were to be made. The prediction proved entirely correct, Volta
himself being the chief discoverer.
Working along lines suggested by Galvani's discovery, Volta constructed
an apparatus made up of a number of disks of two different kinds of metal,
such as tin and silver, arranged alternately, a piece of some moist, porous
substance, like paper or felt, being interposed between each pair of disks.
With this "pile," as it was called, electricity was generated, and by linking
together several such piles an electric battery could be formed.
This invention took the world by storm. Nothing like the enthusiasm it
created in the philosophic world had been known since the invention of the
Leyden jar, more than half a century before. Within a few weeks after
Volta's announcement, batteries made according to his plan were being
experimented with in every important laboratory in Europe.
As the century closed, half the philosophic world was speculating as to
whether "galvanic influence" were a new imponderable, or only a form of
electricity; and the other half was eagerly seeking to discover what new
marvels the battery might reveal. The least imaginative man could see that
here was an invention that would be epoch-making, but the most visionary
dreamer could not even vaguely adumbrate the real measure of its
importance.
It was evident at once that almost any form of galvanic battery, despite
imperfections, was a more satisfactory instrument for generating electricity
than the frictional machine hitherto in use, the advantage lying in the fact
that the current from the galvanic battery could be controlled practically at

will, and that the apparatus itself was inexpensive and required
comparatively little attention. These advantages were soon made apparent
by the practical application of the electric current in several fields.
It will be recalled that despite the energetic endeavors of such
philosophers as Watson, Franklin, Galvani, and many others, the field of
practical application of electricity was very limited at the close of the
eighteenth century. The lightning-rod had come into general use, to be sure,
and its value as an invention can hardly be overestimated. But while it was
the result of extensive electrical discoveries, and is a most practical
instrument, it can hardly be called one that puts electricity to practical use,
but simply acts as a means of warding off the evil effects of a natural
manifestation of electricity. The invention, however, had all the effects of a
mechanism which turned electricity to practical account. But with the
advent of the new kind of electricity the age of practical application began.
DAVY AND ELECTRIC LIGHT
Volta's announcement of his pile was scarcely two months old when two
Englishmen, Messrs. Nicholson and Carlisle, made the discovery that the
current from the galvanic battery had a decided effect upon certain
chemicals, among other things decomposing water into its elements,
hydrogen and oxygen. On May 7, 1800, these investigators arranged the
ends of two brass wires connected with the poles of a voltaic pile,
composed of alternate silver and zinc plates, so that the current coming
from the pile was discharged through a small quantity of "New River
water." "A fine stream of minute bubbles immediately began to flow from
the point of the lower wire in the tube which communicated with the silver,"
wrote Nicholson, "and the opposite point of the upper wire became
tarnished, first deep orange and then black...." The product of gas during
two hours and a half was two-thirtieths of a cubic inch. "It was then mixed
with an equal quantity of common air," continues Nicholson, "and exploded
by the application of a lighted waxen thread."
This demonstration was the beginning of the very important science of
electro-chemistry.
The importance of this discovery was at once recognized by Sir Humphry
Davy, who began experimenting immediately in this new field. He
constructed a series of batteries in various combinations, with which he
attacked the "fixed alkalies," the composition of which was then unknown.

Very shortly he was able to decompose potash into bright metallic globules,
resembling quicksilver. This new substance he named "potassium." Then in
rapid succession the elementary substances sodium, calcium, strontium, and
magnesium were isolated.
It was soon discovered, also, that the new electricity, like the old,
possessed heating power under certain conditions, even to the fusing of
pieces of wire. This observation was probably first made by Frommsdorff,
but it was elaborated by Davy, who constructed a battery of two thousand
cells with which he produced a bright light from points of carbon—the
prototype of the modern arc lamp. He made this demonstration before the
members of the Royal Institution in 1810. But the practical utility of such a
light for illuminating purposes was still a thing of the future. The expense of
constructing and maintaining such an elaborate battery, and the rapid
internal destruction of its plates, together with the constant polarization,
rendered its use in practical illumination out of the question. It was not until
another method of generating electricity was discovered that Davy's
demonstration could be turned to practical account.
In Davy's own account of his experiment he says:
"When pieces of charcoal about an inch long and one-sixth of an inch in
diameter were brought near each other (within the thirtieth or fortieth of an
inch), a bright spark was produced, and more than half the volume of the
charcoal became ignited to whiteness; and, by withdrawing the points from
each other, a constant discharge took place through the heated air, in a space
equal to at least four inches, producing a most brilliant ascending arch of
light, broad and conical in form in the middle. When any substance was
introduced into this arch, it instantly became ignited; platina melted as
readily in it as wax in a common candle; quartz, the sapphire, magnesia,
lime, all entered into fusion; fragments of diamond and points of charcoal
and plumbago seemed to evaporate in it, even when the connection was
made in the receiver of an air-pump; but there was no evidence of their
having previously undergone fusion. When the communication between the
points positively and negatively electrified was made in the air rarefied in
the receiver of the air-pump, the distance at which the discharge took place
increased as the exhaustion was made; and when the atmosphere in the
vessel supported only one-fourth of an inch of mercury in the barometrical
gauge, the sparks passed through a space of nearly half an inch; and, by

withdrawing the points from each other, the discharge was made through
six or seven inches, producing a most brilliant coruscation of purple light;
the charcoal became intensely ignited, and some platina wire attached to it
fused with brilliant scintillations and fell in large globules upon the plate of
the pump. All the phenomena of chemical decomposition were produced
with intense rapidity by this combination."(1)
But this experiment demonstrated another thing besides the possibility of
producing electric light and chemical decomposition, this being the heating
power capable of being produced by the electric current. Thus Davy's
experiment of fusing substances laid the foundation of the modern electric
furnaces, which are of paramount importance in several great commercial
industries.
While some of the results obtained with Davy's batteries were practically
as satisfactory as could be obtained with modern cell batteries, the batteries
themselves were anything but satisfactory. They were expensive, required
constant care and attention, and, what was more important from an
experimental standpoint at least, were not constant in their action except for
a very limited period of time, the current soon "running down." Numerous
experimenters, therefore, set about devising a satisfactory battery, and
when, in 1836, John Frederick Daniell produced the cell that bears his
name, his invention was epoch-making in the history of electrical progress.
The Royal Society considered it of sufficient importance to bestow the
Copley medal upon the inventor, whose device is the direct parent of all
modern galvanic cells. From the time of the advent of the Daniell cell
experiments in electricity were rendered comparatively easy. In the mean
while, however, another great discovery was made.
ELECTRICITY AND MAGNETISM
For many years there had been a growing suspicion, amounting in many
instances to belief in the close relationship existing between electricity and
magnetism. Before the winter of 1815, however, it was a belief that was
surmised but not demonstrated. But in that year it occurred to Jean Christian
Oersted, of Denmark, to pass a current of electricity through a wire held
parallel with, but not quite touching, a suspended magnetic needle. The
needle was instantly deflected and swung out of its position.
"The first experiments in connection with the subject which I am
undertaking to explain," wrote Oersted, "were made during the course of

lectures which I held last winter on electricity and magnetism. From those
experiments it appeared that the magnetic needle could be moved from its
position by means of a galvanic battery—one with a closed galvanic circuit.
Since, however, those experiments were made with an apparatus of small
power, I undertook to repeat and increase them with a large galvanic
battery.
"Let us suppose that the two opposite ends of the galvanic apparatus are
joined by a metal wire. This I shall always call the conductor for the sake of
brevity. Place a rectilinear piece of this conductor in a horizontal position
over an ordinary magnetic needle so that it is parallel to it. The magnetic
needle will be set in motion and will deviate towards the west under that
part of the conductor which comes from the negative pole of the galvanic
battery. If the wire is not more than four-fifths of an inch distant from the
middle of this needle, this deviation will be about forty-five degrees. At a
greater distance the angle of deviation becomes less. Moreover, the
deviation varies according to the strength of the battery. The conductor can
be moved towards the east or west, so long as it remains parallel to the
needle, without producing any other result than to make the deviation
smaller.
"The conductor can consist of several combined wires or metal coils. The
nature of the metal does not alter the result except, perhaps, to make it
greater or less. We have used wires of platinum, gold, silver, brass, and iron,
and coils of lead, tin, and quicksilver with the same result. If the conductor
is interrupted by water, all effect is not cut off, unless the stretch of water is
several inches long.
"The conductor works on the magnetic needle through glass, metals,
wood, water, and resin, through clay vessels and through stone, for when
we placed a glass plate, a metal plate, or a board between the conductor and
the needle the effect was not cut off; even the three together seemed hardly
to weaken the effect, and the same was the case with an earthen vessel, even
when it was full of water. Our experiments also demonstrated that the said
effects were not altered when we used a magnetic needle which was in a
brass case full of water.
"When the conductor is placed in a horizontal plane under the magnetic
needle all the effects we have described take place in precisely the same

way, but in the opposite direction to what took place when the conductor
was in a horizontal plane above the needle.
"If the conductor is moved in a horizontal plane so that it gradually
makes ever-increasing angles with the magnetic meridian, the deviation of
the magnetic needle from the magnetic meridian is increased when the wire
is turned towards the place of the needle; it decreases, on the other hand,
when it is turned away from that place.
"A needle of brass which is hung in the same way as the magnetic needle
is not set in motion by the influence of the conductor. A needle of glass or
rubber likewise remains static under similar experiments. Hence the
electrical conductor affects only the magnetic parts of a substance. That the
electrical current is not confined to the conducting wire, but is
comparatively widely diffused in the surrounding space, is sufficiently
demonstrated from the foregoing observations."(2)
The effect of Oersted's demonstration is almost incomprehensible. By it
was shown the close relationship between magnetism and electricity. It
showed the way to the establishment of the science of electrodynamics;
although it was by the French savant Andre Marie Ampere (1775-1836) that
the science was actually created, and this within the space of one week after
hearing of Oersted's experiment in deflecting the needle. Ampere first
received the news of Oersted's experiment on September 11, 1820, and on
the 18th of the same month he announced to the Academy the fundamental
principles of the science of electro-dynamics—seven days of rapid progress
perhaps unequalled in the history of science.
Ampere's distinguished countryman, Arago, a few months later, gave the
finishing touches to Oersted's and Ampere's discoveries, by demonstrating
conclusively that electricity not only influenced a magnet, but actually
produced magnetism under proper circumstances—a complemental fact
most essential in practical mechanics.
Some four years after Arago's discovery, Sturgeon made the first "electro-
magnet" by winding a soft iron core with wire through which a current of
electricity was passed. This study of electro-magnets was taken up by
Professor Joseph Henry, of Albany, New York, who succeeded in making
magnets of enormous lifting power by winding the iron core with several
coils of wire. One of these magnets, excited by a single galvanic cell of less

than half a square foot of surface, and containing only half a pint of dilute
acids, sustained a weight of six hundred and fifty pounds.
Thus by Oersted's great discovery of the intimate relationship of
magnetism and electricity, with further elaborations and discoveries by
Ampere, Volta, and Henry, and with the invention of Daniell's cell, the way
was laid for putting electricity to practical use. Soon followed the invention
and perfection of the electro-magnetic telegraph and a host of other but
little less important devices.
FARADAY AND ELECTRO-MAGNETIC INDUCTION
With these great discoveries and inventions at hand, electricity became
no longer a toy or a "plaything for philosophers," but of enormous and
growing importance commercially. Still, electricity generated by chemical
action, even in a very perfect cell, was both feeble and expensive, and,
withal, only applicable in a comparatively limited field. Another important
scientific discovery was necessary before such things as electric traction
and electric lighting on a large scale were to become possible; but that
discovery was soon made by Sir Michael Faraday.
Faraday, the son of a blacksmith and a bookbinder by trade, had
interested Sir Humphry Davy by his admirable notes on four of Davy's
lectures, which he had been able to attend. Although advised by the great
scientist to "stick to his bookbinding" rather than enter the field of science,
Faraday became, at twenty-two years of age, Davy's assistant in the Royal
Institution. There, for several years, he devoted all his spare hours to
scientific investigations and experiments, perfecting himself in scientific
technique.
A few years later he became interested, like all the scientists of the time,
in Arago's experiment of rotating a copper disk underneath a suspended
compass-needle. When this disk was rotated rapidly, the needle was
deflected, or even rotated about its axis, in a manner quite inexplicable.
Faraday at once conceived the idea that the cause of this rotation was due to
electricity, induced in the revolving disk—not only conceived it, but put his
belief in writing. For several years, however, he was unable to demonstrate
the truth of his assumption, although he made repeated experiments to
prove it. But in 1831 he began a series of experiments that established
forever the fact of electro-magnetic induction.

In his famous paper, read before the Royal Society in 1831, Faraday
describes the method by which he first demonstrated electro-magnetic
induction, and then explained the phenomenon of Arago's revolving disk.
"About twenty-six feet of copper wire, one-twentieth of an inch in
diameter, were wound round a cylinder of wood as a helix," he said, "the
different spires of which were prevented from touching by a thin interposed
twine. This helix was covered with calico, and then a second wire applied in
the same manner. In this way twelve helices were "superposed, each
containing an average length of wire of twenty-seven feet, and all in the
same direction. The first, third, fifth, seventh, ninth, and eleventh of these
helices were connected at their extremities end to end so as to form one
helix; the others were connected in a similar manner; and thus two principal
helices were produced, closely interposed, having the same direction, not
touching anywhere, and each containing one hundred and fifty-five feet in
length of wire.
One of these helices was connected with a galvanometer, the other with a
voltaic battery of ten pairs of plates four inches square, with double coppers
and well charged; yet not the slightest sensible deflection of the
galvanometer needle could be observed.
"A similar compound helix, consisting of six lengths of copper and six of
soft iron wire, was constructed. The resulting iron helix contained two
hundred and eight feet; but whether the current from the trough was passed
through the copper or the iron helix, no effect upon the other could be
perceived at the galvanometer.
"In these and many similar experiments no difference in action of any
kind appeared between iron and other metals.
"Two hundred and three feet of copper wire in one length were passed
round a large block of wood; other two hundred and three feet of similar
wire were interposed as a spiral between the turns of the first, and metallic
contact everywhere prevented by twine. One of these helices was connected
with a galvanometer and the other with a battery of a hundred pairs of
plates four inches square, with double coppers and well charged. When the
contact was made, there was a sudden and very slight effect at the
galvanometer, and there was also a similar slight effect when the contact
with the battery was broken. But whilst the voltaic current was continuing
to pass through the one helix, no galvanometrical appearances of any effect

like induction upon the other helix could be perceived, although the active
power of the battery was proved to be great by its heating the whole of its
own helix, and by the brilliancy of the discharge when made through
charcoal.
"Repetition of the experiments with a battery of one hundred and twenty
pairs of plates produced no other effects; but it was ascertained, both at this
and at the former time, that the slight deflection of the needle occurring at
the moment of completing the connection was always in one direction, and
that the equally slight deflection produced when the contact was broken was
in the other direction; and, also, that these effects occurred when the first
helices were used.
"The results which I had by this time obtained with magnets led me to
believe that the battery current through one wire did, in reality, induce a
similar current through the other wire, but that it continued for an instant
only, and partook more of the nature of the electrical wave passed through
from the shock of a common Leyden jar than of that from a voltaic battery,
and, therefore, might magnetize a steel needle although it scarcely affected
the galvanometer.
"This expectation was confirmed; for on substituting a small hollow
helix, formed round a glass tube, for the galvanometer, introducing a steel
needle, making contact as before between the battery and the inducing wire,
and then removing the needle before the battery contact was broken, it was
found magnetized.
"When the battery contact was first made, then an unmagnetized needle
introduced, and lastly the battery contact broken, the needle was found
magnetized to an equal degree apparently with the first; but the poles were
of the contrary kinds."(3)
To Faraday these experiments explained the phenomenon of Arago's
rotating disk, the disk inducing the current from the magnet, and, in
reacting, deflecting the needle. To prove this, he constructed a disk that
revolved between the poles of an electro-magnet, connecting the axis and
the edge of the disk with a galvanometer. "... A disk of copper, twelve
inches in diameter, fixed upon a brass axis," he says, "was mounted in
frames so as to be revolved either vertically or horizontally, its edge being
at the same time introduced more or less between the magnetic poles. The
edge of the plate was well amalgamated for the purpose of obtaining good

but movable contact; a part round the axis was also prepared in a similar
manner.
"Conductors or collectors of copper and lead were constructed so as to
come in contact with the edge of the copper disk, or with other forms of
plates hereafter to be described. These conductors we're about four inches
long, one-third of an inch wide, and one-fifth of an inch thick; one end of
each was slightly grooved, to allow of more exact adaptation to the
somewhat convex edge of the plates, and then amalgamated. Copper wires,
one-sixteenth of an inch in thickness, attached in the ordinary manner by
convolutions to the other ends of these conductors, passed away to the
galvanometer.
"All these arrangements being made, the copper disk was adjusted, the
small magnetic poles being about one-half an inch apart, and the edge of the
plate inserted about half their width between them. One of the galvanometer
wires was passed twice or thrice loosely round the brass axis of the plate,
and the other attached to a conductor, which itself was retained by the hand
in contact with the amalgamated edge of the disk at the part immediately
between the magnetic poles. Under these circumstances all was quiescent,
and the galvanometer exhibited no effect. But the instant the plate moved
the galvanometer was influenced, and by revolving the plate quickly the
needle could be deflected ninety degrees or more."(4)
This rotating disk was really a dynamo electric machine in miniature, the
first ever constructed, but whose direct descendants are the ordinary
dynamos. Modern dynamos range in power from little machines operating
machinery requiring only fractions of a horsepower to great dynamos
operating street-car lines and lighting cities; but all are built on the same
principle as Faraday's rotating disk. By this discovery the use of electricity
as a practical and economical motive power became possible.
STORAGE BATTERIES
When the discoveries of Faraday of electro-magnetic induction had made
possible the means of easily generating electricity, the next natural step was
to find a means of storing it or accumulating it. This, however, proved no
easy matter, and as yet a practical storage or secondary battery that is
neither too cumbersome, too fragile, nor too weak in its action has not been
invented. If a satisfactory storage battery could be made, it is obvious that
its revolutionary effects could scarcely be overestimated. In the single field

of aeronautics, it would probably solve the question of aerial navigation.
Little wonder, then, that inventors have sought so eagerly for the invention
of satisfactory storage batteries. As early as 1803 Ritter had attempted to
make such a secondary battery. In 1843 Grove also attempted it. But it was
not until 1859, when Gaston Planche produced his invention, that anything
like a reasonably satisfactory storage battery was made. Planche discovered
that sheets of lead immersed in dilute sulphuric acid were very satisfactory
for the production of polarization effects. He constructed a battery of sheets
of lead immersed in sulphuric acid, and, after charging these for several
hours from the cells of an ordinary Bunsen battery, was able to get currents
of great strength and considerable duration. This battery, however, from its
construction of lead, was necessarily heavy and cumbersome. Faure
improved it somewhat by coating the lead plates with red-lead, thus
increasing the capacity of the cell. Faure's invention gave a fresh impetus to
inventors, and shortly after the market was filled with storage batteries of
various kinds, most of them modifications of Planche's or Faure's. The ardor
of enthusiastic inventors soon flagged, however, for all these storage
batteries proved of little practical account in the end, as compared with
other known methods of generating power.
Three methods of generating electricity are in general use: static or
frictional electricity is generated by "plate" or "static" machines; galvanic,
generated by batteries based on Volta's discovery; and induced, or faradic,
generated either by chemical or mechanical action. There is still another
kind, thermo-electricity, that may be generated in a most simple manner. In
1821 Seebecle, of Berlin, discovered that when a circuit was formed of two
wires of different metals, if there be a difference in temperature at the
juncture of these two metals an electrical current will be established. In this
way heat may be transmitted directly into the energy of the current without
the interposition of the steam-engine. Batteries constructed in this way are
of low resistance, however, although by arranging several of them in
"series," currents of considerable strength can be generated. As yet,
however, they are of little practical importance.
About the middle of the century Clerk-Maxwell advanced the idea that
light waves were really electro-magnetic waves. If this were true and light
proved to be simply one form of electrical energy, then the same would be
true of radiant heat. Maxwell advanced this theory, but failed to substantiate
it by experimental confirmation. But Dr. Heinrich Hertz, a few years later,

by a series of experiments, demonstrated the correctness of Maxwell's
surmises. What are now called "Hertzian waves" are waves apparently
identical with light waves, but of much lower pitch or period. In his
experiments Hertz showed that, under proper conditions, electric sparks
between polished balls were attended by ether waves of the same nature as
those of light, but of a pitch of several millions of vibrations per second.
These waves could be dealt with as if they were light waves—reflected,
refracted, and polarized. These are the waves that are utilized in wireless
telegraphy.
ROENTGEN RAYS, OR X-RAYS
In December of 1895 word came out of Germany of a scientific
discovery that startled the world. It came first as a rumor, little credited;
then as a pronounced report; at last as a demonstration. It told of a new
manifestation of energy, in virtue of which the interior of opaque objects is
made visible to human eyes. One had only to look into a tube containing a
screen of a certain composition, and directed towards a peculiar electrical
apparatus, to acquire clairvoyant vision more wonderful than the discredited
second-sight of the medium. Coins within a purse, nails driven into wood,
spectacles within a leather case, became clearly visible when subjected to
the influence of this magic tube; and when a human hand was held before
the tube, its bones stood revealed in weird simplicity, as if the living,
palpitating flesh about them were but the shadowy substance of a ghost.
Not only could the human eye see these astounding revelations, but the
impartial evidence of inanimate chemicals could be brought forward to
prove that the mind harbored no illusion. The photographic film recorded
the things that the eye might see, and ghostly pictures galore soon gave a
quietus to the doubts of the most sceptical. Within a month of the
announcement of Professor Roentgen's experiments comment upon the "X-
ray" and the "new photography" had become a part of the current gossip of
all Christendom.
It is hardly necessary to say that such a revolutionary thing as the
discovery of a process whereby opaque objects became transparent, or
translucent, was not achieved at a single bound with no intermediate
discoveries. In 1859 the German physicist Julius Plucker (1801-1868)
noticed that when there was an electrical discharge through an exhausted
tube at a low pressure, on the surrounding walls of the tube near the

negative pole, or cathode, appeared a greenish phosphorescence. This
discovery was soon being investigated by a number of other scientists,
among others Hittorf, Goldstein, and Professor (now Sir William) Crookes.
The explanations given of this phenomenon by Professor Crookes concern
us here more particularly, inasmuch as his views did not accord exactly with
those held by the other two scientists, and as his researches were more
directly concerned in the discovery of the Roentgen rays. He held that the
heat and phosphorescence produced in a low-pressure tube were caused by
streams of particles, projected from the cathode with great velocity, striking
the sides of the glass tube. The composition of the glass seemed to enter
into this phosphorescence also, for while lead glass produced blue
phosphorescence, soda glass produced a yellowish green. The composition
of the glass seemed to be changed by a long-continued pelting of these
particles, the phosphorescence after a time losing its initial brilliancy,
caused by the glass becoming "tired," as Professor Crookes said. Thus when
some opaque substance, such as iron, is placed between the cathode and the
sides of the glass tube so that it casts a shadow in a certain spot on the glass
for some little time, it is found on removing the opaque substance or
changing its position that the area of glass at first covered by the shadow
now responded to the rays in a different manner from the surrounding glass.
The peculiar ray's, now known as the cathode rays, not only cast a
shadow, but are deflected by a magnet, so that the position of the
phosphorescence on the sides of the tube may be altered by the proximity of
a powerful magnet. From this it would seem that the rays are composed of
particles charged with negative electricity, and Professor J. J. Thomson has
modified the experiment of Perrin to show that negative electricity is
actually associated with the rays. There is reason for believing, therefore,
that the cathode rays are rapidly moving charges of negative electricity. It is
possible, also, to determine the velocity at which these particles are moving
by measuring the deflection produced by the magnetic field.
From the fact that opaque substances cast a shadow in these rays it was
thought at first that all solids were absolutely opaque to them. Hertz,
however, discovered that a small amount of phosphorescence occurred on
the glass even when such opaque substances as gold-leaf or aluminium foil
were interposed between the cathode and the sides of the tube. Shortly
afterwards Lenard discovered that the cathode rays can be made to pass

from the inside of a discharge tube to the outside air. For convenience these
rays outside the tube have since been known as "Lenard rays."
In the closing days of December, 1895, Professor Wilhelm Konrad
Roentgen, of Wurzburg, announced that he had made the discovery of the
remarkable effect arising from the cathode rays to which reference was
made above. He found that if a plate covered with a phosphorescent
substance is placed near a discharge tube exhausted so highly that the
cathode rays produced a green phosphorescence, this plate is made to glow
in a peculiar manner. The rays producing this glow were not the cathode
rays, although apparently arising from them, and are what have since been
called the Roentgen rays, or X-rays.
Roentgen found that a shadow is thrown upon the screen by substances
held between it and the exhausted tube, the character of the shadow
depending upon the density of the substance. Thus metals are almost
completely opaque to the rays; such substances as bone much less so, and
ordinary flesh hardly so at all. If a coin were held in the hand that had been
interposed between the tube and the screen the picture formed showed the
coin as a black shadow; and the bones of the hand, while casting a distinct
shadow, showed distinctly lighter; while the soft tissues produced scarcely
any shadow at all. The value of such a discovery was obvious from the first;
and was still further enhanced by the discovery made shortly that,
photographic plates are affected by the rays, thus making it possible to
make permanent photographic records of pictures through what we know as
opaque substances.
What adds materially to the practical value of Roentgen's discovery is the
fact that the apparatus for producing the X-rays is now so simple and
relatively inexpensive that it is within the reach even of amateur scientists.
It consists essentially of an induction coil attached either to cells or a street-
current plug for generating the electricity, a focus tube, and a
phosphorescence screen. These focus tubes are made in various shapes, but
perhaps the most popular are in the form of a glass globe, not unlike an
ordinary small-sized water-bottle, this tube being closed and exhausted, and
having the two poles (anode and cathode) sealed into the glass walls, but
protruding at either end for attachment to the conducting wires from the
induction coil. This tube may be mounted on a stand at a height convenient
for manipulation. The phosphorescence screen is usually a plate covered

with some platino-cyanide and mounted in the end of a box of convenient
size, the opposite end of which is so shaped that it fits the contour of the
face, shutting out the light and allowing the eyes of the observer to focalize
on the screen at the end. For making observations the operator has simply to
turn on the current of electricity and apply the screen to his eyes, pointing it
towards the glowing tube, when the shadow of any substance interposed
between the tube and the screen will appear upon the phosphorescence
plate.
The wonderful shadow pictures produced on the phosphorescence screen,
or the photographic plate, would seem to come from some peculiar form of
light, but the exact nature of these rays is still an open question. Whether
the Roentgen rays are really a form of light—that is, a form of "electro-
magnetic disturbance propagated through ether," is not fully determined.
Numerous experiments have been undertaken to determine this, but as yet
no proof has been found that the rays are a form of light, although there
appears to be nothing in their properties inconsistent with their being so.
For the moment most investigators are content to admit that the term X-ray
virtually begs the question as to the intimate nature of the form of energy
involved.

VIII. THE CONSERVATION OF ENERGY
As we have seen, it was in 1831 that Faraday opened up the field of
magneto-electricity. Reversing the experiments of his predecessors, who
had found that electric currents may generate magnetism, he showed that
magnets have power under certain circumstances to generate electricity; he
proved, indeed, the interconvertibility of electricity and magnetism. Then he
showed that all bodies are more or less subject to the influence of
magnetism, and that even light may be affected by magnetism as to its
phenomena of polarization. He satisfied himself completely of the true
identity of all the various forms of electricity, and of the convertibility of
electricity and chemical action. Thus he linked together light, chemical
affinity, magnetism, and electricity. And, moreover, he knew full well that
no one of these can be produced in indefinite supply from another.
"Nowhere," he says, "is there a pure creation or production of power
without a corresponding exhaustion of something to supply it."
When Faraday wrote those words in 1840 he was treading on the very
heels of a greater generalization than any which he actually formulated; nay,
he had it fairly within his reach. He saw a great truth without fully realizing
its import; it was left for others, approaching the same truth along another
path, to point out its full significance.
The great generalization which Faraday so narrowly missed is the truth
which since then has become familiar as the doctrine of the conservation of
energy—the law that in transforming energy from one condition to another
we can never secure more than an equivalent quantity; that, in short, "to
create or annihilate energy is as impossible as to create or annihilate matter;
and that all the phenomena of the material universe consist in
transformations of energy alone." Some philosophers think this the greatest
generalization ever conceived by the mind of man. Be that as it may, it is
surely one of the great intellectual landmarks of the nineteenth century. It
stands apart, so stupendous and so far-reaching in its implications that the
generation which first saw the law developed could little appreciate it; only
now, through the vista of half a century, do we begin to see it in its true
proportions.

A vast generalization such as this is never a mushroom growth, nor does
it usually spring full grown from the mind of any single man. Always a
number of minds are very near a truth before any one mind fully grasps it.
Pre-eminently true is this of the doctrine of the conservation of energy. Not
Faraday alone, but half a dozen different men had an inkling of it before it
gained full expression; indeed, every man who advocated the undulatory
theory of light and heat was verging towards the goal. The doctrine of
Young and Fresnel was as a highway leading surely on to the wide plain of
conservation. The phenomena of electro-magnetism furnished another such
highway. But there was yet another road which led just as surely and even
more readily to the same goal. This was the road furnished by the
phenomena of heat, and the men who travelled it were destined to outstrip
their fellow-workers; though, as we have seen, wayfarers on other roads
were within hailing distance when the leaders passed the mark.
In order to do even approximate justice to the men who entered into the
great achievement, we must recall that just at the close of the eighteenth
century Count Rumford and Humphry Davy independently showed that
labor may be transformed into heat; and correctly interpreted this fact as
meaning the transformation of molar into molecular motion. We can hardly
doubt that each of these men of genius realized—vaguely, at any rate—that
there must be a close correspondence between the amount of the molar and
the molecular motions; hence that each of them was in sight of the law of
the mechanical equivalent of heat. But neither of them quite grasped or
explicitly stated what each must vaguely have seen; and for just a quarter of
a century no one else even came abreast their line of thought, let alone
passing it.
But then, in 1824, a French philosopher, Sadi Carnot, caught step with
the great Englishmen, and took a long leap ahead by explicitly stating his
belief that a definite quantity of work could be transformed into a definite
quantity of heat, no more, no less. Carnot did not, indeed, reach the clear
view of his predecessors as to the nature of heat, for he still thought it a
form of "imponderable" fluid; but he reasoned none the less clearly as to its
mutual convertibility with mechanical work. But important as his
conclusions seem now that we look back upon them with clearer vision,
they made no impression whatever upon his contemporaries. Carnot's work
in this line was an isolated phenomenon of historical interest, but it did not

enter into the scheme of the completed narrative in any such way as did the
work of Rumford and Davy.
The man who really took up the broken thread where Rumford and Davy
had dropped it, and wove it into a completed texture, came upon the scene
in 1840. His home was in Manchester, England; his occupation that of a
manufacturer. He was a friend and pupil of the great Dr. Dalton. His name
was James Prescott Joule. When posterity has done its final juggling with
the names of the nineteenth century, it is not unlikely that the name of this
Manchester philosopher will be a household word, like the names of
Aristotle, Copernicus, and Newton.
For Joule's work it was, done in the fifth decade of the century, which
demonstrated beyond all cavil that there is a precise and absolute
equivalence between mechanical work and heat; that whatever the form of
manifestation of molar motion, it can generate a definite and measurable
amount of heat, and no more. Joule found, for example, that at the sea-level
in Manchester a pound weight falling through seven hundred and seventy-
two feet could generate enough heat to raise the temperature of a pound of
water one degree Fahrenheit. There was nothing haphazard, nothing
accidental, about this; it bore the stamp of unalterable law. And Joule
himself saw, what others in time were made to see, that this truth is merely
a particular case within a more general law. If heat cannot be in any sense
created, but only made manifest as a transformation of another kind of
motion, then must not the same thing be true of all those other forms of
"force"—light, electricity, magnetism—which had been shown to be so
closely associated, so mutually convertible, with heat? All analogy seemed
to urge the truth of this inference; all experiment tended to confirm it. The
law of the mechanical equivalent of heat then became the main corner-stone
of the greater law of the conservation of energy.
But while this citation is fresh in mind, we must turn our attention with
all haste to a country across the Channel—to Denmark, in short—and learn
that even as Joule experimented with the transformation of heat, a
philosopher of Copenhagen, Colding by name, had hit upon the same idea,
and carried it far towards a demonstration. And then, without pausing, we
must shift yet again, this time to Germany, and consider the work of three
other men, who independently were on the track of the same truth, and two
of whom, it must be admitted, reached it earlier than either Joule or

Colding, if neither brought it to quite so clear a demonstration. The names
of these three Germans are Mohr, Mayer, and Helmholtz. Their share in
establishing the great doctrine of conservation must now claim our
attention.
As to Karl Friedrich Mohr, it may be said that his statement of the
doctrine preceded that of any of his fellows, yet that otherwise it was
perhaps least important. In 1837 this thoughtful German had grasped the
main truth, and given it expression in an article published in the Zeitschrift
fur Physik, etc. But the article attracted no attention whatever, even from
Mohr's own countrymen. Still, Mohr's title to rank as one who
independently conceived the great truth, and perhaps conceived it before
any other man in the world saw it as clearly, even though he did not
demonstrate its validity, is not to be disputed.
It was just five years later, in 1842, that Dr. Julius Robert Mayer,
practising physician in the little German town of Heilbronn, published a
paper in Liebig's Annalen on "The Forces of Inorganic Nature," in which
not merely the mechanical theory of heat, but the entire doctrine of the
conservation of energy, is explicitly if briefly stated. Two years earlier Dr.
Mayer, while surgeon to a Dutch India vessel cruising in the tropics, had
observed that the venous blood of a patient seemed redder than venous
blood usually is observed to be in temperate climates. He pondered over
this seemingly insignificant fact, and at last reached the conclusion that the
cause must be the lesser amount of oxidation required to keep up the body
temperature in the tropics. Led by this reflection to consider the body as a
machine dependent on outside forces for its capacity to act, he passed on
into a novel realm of thought, which brought him at last to independent
discovery of the mechanical theory of heat, and to the first full and
comprehensive appreciation of the great law of conservation. Blood-letting,
the modern physician holds, was a practice of very doubtful benefit, as a
rule, to the subject; but once, at least, it led to marvellous results. No straw
is go small that it may not point the receptive mind of genius to new and
wonderful truths.
MAYER'S PAPER OF 1842
The paper in which Mayer first gave expression to his revolutionary ideas
bore the title of "The Forces of Inorganic Nature," and was published in
1842. It is one of the gems of scientific literature, and fortunately it is not

too long to be quoted in its entirety. Seldom if ever was a great
revolutionary doctrine expounded in briefer compass:
"What are we to understand by 'forces'? and how are different forces
related to each other? The term force conveys for the most part the idea of
something unknown, unsearchable, and hypothetical; while the term matter,
on the other hand, implies the possession, by the object in question, of such
definite properties as weight and extension. An attempt, therefore, to render
the idea of force equally exact with that of matter is one which should be
welcomed by all those who desire to have their views of nature clear and
unencumbered by hypothesis.
"Forces are causes; and accordingly we may make full application in
relation to them of the principle causa aequat effectum. If the cause c has
the effect e, then c = e; if, in its turn, e is the cause of a second effect of f,
we have e = f, and so on: c = e = f... = c. In a series of causes and effects, a
term or a part of a term can never, as is apparent from the nature of an
equation, become equal to nothing. This first property of all causes we call
their indestructibility.
"If the given cause c has produced an effect e equal to itself, it has in that
very act ceased to be—c has become e. If, after the production of e, c still
remained in the whole or in part, there must be still further effects
corresponding to this remaining cause: the total effect of c would thus be >
e, which would be contrary to the supposition c = e. Accordingly, since c
becomes e, and e becomes f, etc., we must regard these various magnitudes
as different forms under which one and the same object makes its
appearance. This capability of assuming various forms is the second
essential property of all causes. Taking both properties together, we may
say, causes an INDESTRUCTIBLE quantitatively, and quantitatively
CONVERTIBLE objects.
"There occur in nature two causes which apparently never pass one into
the other," said Mayer. "The first class consists of such causes as possess
the properties of weight and impenetrability. These are kinds of matter. The
other class is composed of causes which are wanting in the properties just
mentioned—namely, forces, called also imponderables, from the negative
property that has been indicated. Forces are therefore INDESTRUCTIBLE,
CONVERTIBLE, IMPONDERABLE OBJECTS.

"As an example of causes and effects, take matter: explosive gas, H + O,
and water, HO, are related to each other as cause and effect; therefore H +
O = HO. But if H + O becomes HO, heat, cal., makes its appearance as well
as water; this heat must likewise have a cause, x, and we have therefore H +
O + X = HO + cal. It might be asked, however, whether H + O is really =
HO, and x = cal., and not perhaps H + O = cal., and x = HO, whence the
above equation could equally be deduced; and so in many other cases. The
phlogistic chemists recognized the equation between cal. and x, or
phlogiston as they called it, and in so doing made a great step in advance;
but they involved themselves again in a system of mistakes by putting x in
place of O. In this way they obtained H = HO + x.
"Chemistry teaches us that matter, as a cause, has matter for its effect; but
we may say with equal justification that to force as a cause corresponds
force as effect. Since c = e, and e = c, it is natural to call one term of an
equation a force, and the other an effect of force, or phenomenon, and to
attach different notions to the expression force and phenomenon. In brief,
then, if the cause is matter, the effect is matter; if the cause is a force, the
effect is also a force.
"The cause that brings about the raising of a weight is a force. The effect
of the raised weight is, therefore, also a force; or, expressed in a more
general form, SEPARATION IN SPACE OF PONDERABLE OBJECTS IS
A FORCE; and since this force causes the fall of bodies, we call it
FALLING FORCE. Falling force and fall, or, still more generally, falling
force and motion, are forces related to each other as cause and effect—
forces convertible into each other—two different forms of one and the same
object. For example, a weight resting on the ground is not a force: it is
neither the cause of motion nor of the lifting of another weight. It becomes
so, however, in proportion as it is raised above the ground. The cause—that
is, the distance between a weight and the earth, and the effect, or the
quantity of motion produced, bear to each other, as shown by mechanics, a
constant relation.
"Gravity being regarded as the cause of the falling of bodies, a
gravitating force is spoken of; and thus the ideas of PROPERTY and of
FORCE are confounded with each other. Precisely that which is the
essential attribute of every force—that is, the UNION of indestructibility
with convertibility—is wanting in every property: between a property and a

force, between gravity and motion, it is therefore impossible to establish the
equation required for a rightly conceived causal relation. If gravity be called
a force, a cause is supposed which produces effects without itself
diminishing, and incorrect conceptions of the causal connections of things
are thereby fostered. In order that a body may fall, it is just as necessary that
it be lifted up as that it should be heavy or possess gravity. The fall of
bodies, therefore, ought not to be ascribed to their gravity alone. The
problem of mechanics is to develop the equations which subsist between
falling force and motion, motion and falling force, and between different
motions. Here is a case in point: The magnitude of the falling force v is
directly proportional (the earth's radius being assumed—oo) to the
magnitude of the mass m, and the height d, to which it is raised—that is, v =
md. If the height d = l, to which the mass m is raised, is transformed into
the final velocity c = l of this mass, we have also v = mc; but from the
known relations existing between d and c, it results that, for other values of
d or of c, the measure of the force v is mc squared; accordingly v = md =
mcsquared. The law of the conservation of vis viva is thus found to be
based on the general law of the indestructibility of causes.
"In many cases we see motion cease without having caused another
motion or the lifting of a weight. But a force once in existence cannot be
annihilated—it can only change its form. And the question therefore arises,
what other forms is force, which we have become acquainted with as falling
force and motion, capable of assuming? Experience alone can lead us to a
conclusion on this point. That we may experiment to advantage, we must
select implements which, besides causing a real cessation of motion, are as
little as possible altered by the objects to be examined. For example, if we
rub together two metal plates, we see motion disappear, and heat, on the
other hand, make its appearance, and there remains to be determined only
whether MOTION is the cause of heat. In order to reach a decision on this
point, we must discuss the question whether, in the numberless cases in
which the expenditure of motion is accompanied by the appearance of heat,
the motion has not some other effect than the production of heat, and the
heat some other cause than the motion.
"A serious attempt to ascertain the effects of ceasing motion has never
been made. Without wishing to exclude a priori the hypothesis which it may
be possible to establish, therefore, we observe only that, as a rule, this effect
cannot be supposed to be an alteration in the state of aggregation of the

moved (that is, rubbing, etc.) bodies. If we assume that a certain quantity of
motion v is expended in the conversion of a rubbing substance m into n, we
must then have m + v - n, and n = m + v; and when n is reconverted into m,
v must appear again in some form or other.
"By the friction of two metallic plates continued for a very long time, we
can gradually cause the cessation of an immense quantity of movement; but
would it ever occur to us to look for even the smallest trace of the force
which has disappeared in the metallic dust that we could collect, and to try
to regain it thence? We repeat, the motion cannot have been annihilated; and
contrary, or positive and negative, motions cannot be regarded as = o any
more than contrary motions can come out of nothing, or a weight can raise
itself.
"Without the recognition of a causal relation between motion and heat, it
is just as difficult to explain the production of heat as it is to give any
account of the motion that disappears. The heat cannot be derived from the
diminution of the volume of the rubbing substances. It is well known that
two pieces of ice may be melted by rubbing them together in vacuo; but let
any one try to convert ice into water by pressure, however enormous. The
author has found that water undergoes a rise of temperature when shaken
violently. The water so heated (from twelve to thirteen degrees centigrade)
has a greater bulk after being shaken than it had before. Whence now comes
this quantity of heat, which by repeated shaking may be called into
existence in the same apparatus as often as we please? The vibratory
hypothesis of heat is an approach towards the doctrine of heat being the
effect of motion, but it does not favor the admission of this causal relation
in its full generality. It rather lays the chief stress on restless oscillations.
"If it be considered as now established that in many cases no other effect
of motion can be traced except heat, and that no other cause than motion
can be found for the heat that is produced, we prefer the assumption that
heat proceeds from motion to the assumption of a cause without effect and
of an effect without a cause. Just as the chemist, instead of allowing oxygen
and hydrogen to disappear without further investigation, and water to be
produced in some inexplicable manner, establishes a connection between
oxygen and hydrogen on the one hand, and water on the other.
"We may conceive the natural connection existing between falling force,
motion, and heat as follows: We know that heat makes its appearance when

the separate particles of a body approach nearer to each other; condensation
produces heat. And what applies to the smallest particles of matter, and the
smallest intervals between them, must also apply to large masses and to
measurable distances. The falling of a weight is a diminution of the bulk of
the earth, and must therefore without doubt be related to the quantity of heat
thereby developed; this quantity of heat must be proportional to the
greatness of the weight and its distance from the ground. From this point of
view we are easily led to the equations between falling force, motion, and
heat that have already been discussed.
"But just as little as the connection between falling force and motion
authorizes the conclusion that the essence of falling force is motion, can
such a conclusion be adopted in the case of heat. We are, on the contrary,
rather inclined to infer that, before it can become heat, motion must cease to
exist as motion, whether simple, or vibratory, as in the case of light and
radiant heat, etc.
"If falling force and motion are equivalent to heat, heat must also
naturally be equivalent to motion and falling force. Just as heat appears as
an EFFECT of the diminution of bulk and of the cessation of motion, so
also does heat disappear as a CAUSE when its effects are produced in the
shape of motion, expansion, or raising of weight.
"In water-mills the continual diminution in bulk which the earth
undergoes, owing to the fall of the water, gives rise to motion, which
afterwards disappears again, calling forth unceasingly a great quantity of
heat; and, inversely, the steam-engine serves to decompose heat again into
motion or the raising of weights. A locomotive with its train may be
compared to a distilling apparatus; the heat applied under the boiler passes
off as motion, and this is deposited again as heat at the axles of the wheels."
Mayer then closes his paper with the following deduction: "The solution
of the equations subsisting between falling force and motion requires that
the space fallen through in a given time—e. g., the first second—should be
experimentally determined. In like manner, the solution of the equations
subsisting between falling force and motion on the one hand and heat on the
other requires an answer to the question, How great is the quantity of heat
which corresponds to a given quantity of motion or falling force? For
instance, we must ascertain how high a given weight requires to be raised
above the ground in order that its falling force maybe equivalent to the

raising of the temperature of an equal weight of water from 0 degrees to 1
degrees centigrade. The attempt to show that such an equation is the
expression of a physical truth may be regarded as the substance of the
foregoing remarks.

"By applying the principles that have been set forth to the relations
subsisting between the temperature and the volume of gases, we find
that the sinking of a mercury column by which a gas is compressed is
equivalent to the quantity of heat set free by the compression; and
hence it follows, the ratio between the capacity for heat of air under
constant pressure and its capacity under constant volume being taken as
= 1.421, that the warming of a given weight of water from 0 degrees to
equal weight from the height of about three hundred and sixty-five
metres. If we compare with this result the working of our best
steam-engines, we see how small a part only of the heat applied under
the boiler is really transformed into motion or the raising of weights;
and this may serve as justification for the attempts at the profitable
production of motion by some other method than the expenditure of the
chemical difference between carbon and oxygen—more particularly by
the transformation into motion of electricity obtained by chemical
means."(1)

MAYER AND HELMHOLTZ
Here, then, was this obscure German physician, leading the humdrum life
of a village practitioner, yet seeing such visions as no human being in the
world had ever seen before.
The great principle he had discovered became the dominating thought of
his life, and filled all his leisure hours. He applied it far and wide, amid all
the phenomena of the inorganic and organic worlds. It taught him that both
vegetables and animals are machines, bound by the same laws that hold
sway over inorganic matter, transforming energy, but creating nothing. Then
his mind reached out into space and met a universe made up of questions.
Each star that blinked down at him as he rode in answer to a night-call
seemed an interrogation-point asking, How do I exist? Why have I not long
since burned out if your theory of conservation be true? No one had hitherto
even tried to answer that question; few had so much as realized that it
demanded an answer. But the Heilbronn physician understood the question
and found an answer. His meteoric hypothesis, published in 1848, gave for
the first time a tenable explanation of the persistent light and heat of our sun
and the myriad other suns—an explanation to which we shall recur in
another connection.
All this time our isolated philosopher, his brain aflame with the glow of
creative thought, was quite unaware that any one else in the world was

working along the same lines. And the outside world was equally heedless
of the work of the Heilbronn physician. There was no friend to inspire
enthusiasm and give courage, no kindred spirit to react on this masterful but
lonely mind. And this is the more remarkable because there are few other
cases where a master-originator in science has come upon the scene except
as the pupil or friend of some other master-originator. Of the men we have
noticed in the present connection, Young was the friend and confrere of
Davy; Davy, the protege of Rumford; Faraday, the pupil of Davy; Fresnel,
the co-worker with Arago; Colding, the confrere of Oersted; Joule, the pupil
of Dalton. But Mayer is an isolated phenomenon—one of the lone
mountain-peak intellects of the century. That estimate may be exaggerated
which has called him the Galileo of the nineteenth century, but surely no
lukewarm praise can do him justice.
Yet for a long time his work attracted no attention whatever. In 1847,
when another German physician, Hermann von Helmholtz, one of the most
massive and towering intellects of any age, had been independently led to
comprehension of the doctrine of the conservation of energy and published
his treatise on the subject, he had hardly heard of his countryman Mayer.
When he did hear of him, however, he hastened to renounce all claim to the
doctrine of conservation, though the world at large gives him credit of
independent even though subsequent discovery.
JOULE'S PAPER OF 1843
Meantime, in England, Joule was going on from one experimental
demonstration to another, oblivious of his German competitors and almost
as little noticed by his own countrymen. He read his first paper before the
chemical section of the British Association for the Advancement of Science
in 1843, and no one heeded it in the least. It is well worth our while,
however, to consider it at length. It bears the title, "On the Calorific Effects
of Magneto-Electricity, and the Mechanical Value of Heat." The full text, as
published in the Report of the British Association, is as follows:
"Although it has been long known that fine platinum wire can be ignited
by magneto-electricity, it still remained a matter of doubt whether heat was
evolved by the COILS in which the magneto-electricity was generated; and
it seemed indeed not unreasonable to suppose that COLD was produced
there in order to make up for the heat evolved by the other part of the
circuit. The author therefore has endeavored to clear up this uncertainty by

experiment. His apparatus consisted of a small compound electro-magnet,
immersed in water, revolving between the poles of a powerful stationary
magnet. The magneto-electricity developed in the coils of the revolving
electro-magnet was measured by an accurate galvanometer; and the
temperature of the water was taken before and after each experiment by a
very delicate thermometer. The influence of the temperature of the
surrounding atmospheric air was guarded against by covering the revolving
tube with flannel, etc., and by the adoption of a system of interpolation. By
an extensive series of experiments with the above apparatus the author
succeeded in proving that heat is evolved by the coils of the magneto-
electrical machine, as well as by any other part of the circuit, in proportion
to the resistance to conduction of the wire and the square of the current; the
magneto having, under comparable circumstances, the same calorific power
as the voltaic electricity.
"Professor Jacobi, of St. Petersburg, bad shown that the motion of an
electro-magnetic machine generates magneto-electricity in opposition to the
voltaic current of the battery. The author had observed the same
phenomenon on arranging his apparatus as an electro-magnetic machine;
but had found that no additional heat was evolved on account of the conflict
of forces in the coil of the electro-magnet, and that the heat evolved by the
coil remained, as before, proportional to the square of the current. Again, by
turning the machine contrary to the direction of the attractive forces, so as
to increase the intensity of the voltaic current by the assistance of the
magneto-electricity, he found that the evolution of heat was still
proportional to the square of the current. The author discovered, therefore,
that the heat evolved by the voltaic current is invariably proportional to the
square of the current, however the intensity of the current may be varied by
magnetic induction. But Dr. Faraday has shown that the chemical effects of
the current are simply as its quantity. Therefore he concluded that in the
electro-magnetic engine a part of the heat due to the chemical actions of the
battery is lost by the circuit, and converted into mechanical power; and that
when the electro-magnetic engine is turned CONTRARY to the direction of
the attractive forces, a greater quantity of heat is evolved by the circuit than
is due to the chemical reactions of the battery, the over-plus quantity being
produced by the conversion of the mechanical force exerted in turning the
machine. By a dynamometrical apparatus attached to his machine, the
author has ascertained that, in all the above cases, a quantity of heat,

capable of increasing the temperature of a pound of water by one degree of
Fahrenheit's scale, is equal to the mechanical force capable of raising a
weight of about eight hundred and thirty pounds to the height of one foot."
(2)
JOULE OR MAYER?
Two years later Joule wished to read another paper, but the chairman
hinted that time was limited, and asked him to confine himself to a brief
verbal synopsis of the results of his experiments. Had the chairman but
known it, he was curtailing a paper vastly more important than all the other
papers of the meeting put together. However, the synopsis was given, and
one man was there to hear it who had the genius to appreciate its
importance. This was William Thomson, the present Lord Kelvin, now
known to all the world as among the greatest of natural philosophers, but
then only a novitiate in science. He came to Joule's aid, started rolling the
ball of controversy, and subsequently associated himself with the
Manchester experimenter in pursuing his investigations.
But meantime the acknowledged leaders of British science viewed the
new doctrine askance. Faraday, Brewster, Herschel—those were the great
names in physics at that day, and no one of them could quite accept the new
views regarding energy. For several years no older physicist, speaking with
recognized authority, came forward in support of the doctrine of
conservation. This culminating thought of the first half of the nineteenth
century came silently into the world, unheralded and unopposed. The fifth
decade of the century had seen it elaborated and substantially demonstrated
in at least three different countries, yet even the leaders of thought did not
so much as know of its existence. In 1853 Whewell, the historian of the
inductive sciences, published a second edition of his history, and, as Huxley
has pointed out, he did not so much as refer to the revolutionizing thought
which even then was a full decade old.
By this time, however, the battle was brewing. The rising generation saw
the importance of a law which their elders could not appreciate, and soon it
was noised abroad that there were more than one claimant to the honor of
discovery. Chiefly through the efforts of Professor Tyndall, the work of
Mayer became known to the British public, and a most regrettable
controversy ensued between the partisans of Mayer and those of Joule—a
bitter controversy, in which Davy's contention that science knows no

country was not always regarded, and which left its scars upon the hearts
and minds of the great men whose personal interests were involved.
And so to this day the question who is the chief discoverer of the law of
the conservation of energy is not susceptible of a categorical answer that
would satisfy all philosophers. It is generally held that the first choice lies
between Joule and Mayer. Professor Tyndall has expressed the belief that in
future each of these men will be equally remembered in connection with
this work. But history gives us no warrant for such a hope. Posterity in the
long run demands always that its heroes shall stand alone. Who remembers
now that Robert Hooke contested with Newton the discovery of the doctrine
of universal gravitation? The judgment of posterity is unjust, but it is
inexorable. And so we can little doubt that a century from now one name
will be mentioned as that of the originator of the great doctrine of the
conservation of energy. The man whose name is thus remembered will
perhaps be spoken of as the Galileo, the Newton, of the nineteenth century;
but whether the name thus dignified by the final verdict of history will be
that of Colding, Mohr, Mayer, Helmholtz, or Joule, is not as, yet decided.
LORD KELVIN AND THE DISSIPATION OF ENERGY
The gradual permeation of the field by the great doctrine of conservation
simply repeated the history of the introduction of every novel and
revolutionary thought. Necessarily the elder generation, to whom all forms
of energy were imponderable fluids, must pass away before the new
conception could claim the field. Even the word energy, though Young had
introduced it in 1807, did not come into general use till some time after the
middle of the century. To the generality of philosophers (the word physicist
was even less in favor at this time) the various forms of energy were still
subtile fluids, and never was idea relinquished with greater unwillingness
than this. The experiments of Young and Fresnel had convinced a large
number of philosophers that light is a vibration and not a substance; but so
great an authority as Biot clung to the old emission idea to the end of his
life, in 1862, and held a following.
Meantime, however, the company of brilliant young men who had just
served their apprenticeship when the doctrine of conservation came upon
the scene had grown into authoritative positions, and were battling actively
for the new ideas. Confirmatory evidence that energy is a molecular motion
and not an "imponderable" form of matter accumulated day by day. The

experiments of two Frenchmen, Hippolyte L. Fizeau and Leon Foucault,
served finally to convince the last lingering sceptics that light is an
undulation; and by implication brought heat into the same category, since
James David Forbes, the Scotch physicist, had shown in 1837 that radiant
heat conforms to the same laws of polarization and double refraction that
govern light. But, for that matter, the experiments that had established the
mechanical equivalent of heat hardly left room for doubt as to the
immateriality of this "imponderable." Doubters had indeed, expressed
scepticism as to the validity of Joule's experiments, but the further
researches, experimental and mathematical, of such workers as Thomson
(Lord Kelvin), Rankine, and Tyndall in Great Britain, of Helmholtz and
Clausius in Germany, and of Regnault in France, dealing with various
manifestations of heat, placed the evidence beyond the reach of criticism.
Out of these studies, just at the middle of the century, to which the
experiments of Mayer and Joule had led, grew the new science of thermo-
dynamics. Out of them also grew in the mind of one of the investigators a
new generalization, only second in importance to the doctrine of
conservation itself. Professor William Thomson (Lord Kelvin) in his studies
in thermodynamics was early impressed with the fact that whereas all the
molar motion developed through labor or gravity could be converted into
heat, the process is not fully reversible. Heat can, indeed, be converted into
molar motion or work, but in the process a certain amount of the heat is
radiated into space and lost. The same thing happens whenever any other
form of energy is converted into molar motion. Indeed, every transmutation
of energy, of whatever character, seems complicated by a tendency to
develop heat, part of which is lost. This observation led Professor Thomson
to his doctrine of the dissipation of energy, which he formulated before the
Royal Society of Edinburgh in 1852, and published also in the
Philosophical Magazine the same year, the title borne being, "On a
Universal Tendency in Nature to the Dissipation of Mechanical Energy."
From the principle here expressed Professor Thomson drew the startling
conclusion that, "since any restoration of this mechanical energy without
more than an equivalent dissipation is impossible," the universe, as known
to us, must be in the condition of a machine gradually running down; and in
particular that the world we live on has been within a finite time unfit for
human habitation, and must again become so within a finite future. This
thought seems such a commonplace to-day that it is difficult to realize how

startling it appeared half a century ago. A generation trained, as ours has
been, in the doctrines of the conservation and dissipation of energy as the
very alphabet of physical science can but ill appreciate the mental attitude
of a generation which for the most part had not even thought it
problematical whether the sun could continue to give out heat and light
forever. But those advance thinkers who had grasped the import of the
doctrine of conservation could at once appreciate the force of Thomson's
doctrine of dissipation, and realize the complementary character of the two
conceptions.
Here and there a thinker like Rankine did, indeed, attempt to fancy
conditions under which the energy lost through dissipation might be
restored to availability, but no such effort has met with success, and in time
Professor Thomson's generalization and his conclusions as to the
consequences of the law involved came to be universally accepted.
The introduction of the new views regarding the nature of energy
followed, as I have said, the course of every other growth of new ideas.
Young and imaginative men could accept the new point of view; older
philosophers, their minds channelled by preconceptions, could not get into
the new groove. So strikingly true is this in the particular case now before
us that it is worth while to note the ages at the time of the revolutionary
experiments of the men whose work has been mentioned as entering into
the scheme of evolution of the idea that energy is merely a manifestation of
matter in motion. Such a list will tell the story better than a volume of
commentary.
Observe, then, that Davy made his epochal experiment of melting ice by
friction when he was a youth of twenty. Young was no older when he made
his first communication to the Royal Society, and was in his twenty-seventh
year when he first actively espoused the undulatory theory. Fresnel was
twenty-six when he made his first important discoveries in the same field;
and Arago, who at once became his champion, was then but two years his
senior, though for a decade he had been so famous that one involuntarily
thinks of him as belonging to an elder generation.
Forbes was under thirty when he discovered the polarization of heat,
which pointed the way to Mohr, then thirty-one, to the mechanical
equivalent. Joule was twenty-two in 1840, when his great work was begun;
and Mayer, whose discoveries date from the same year, was then twenty-

six, which was also the age of Helmholtz when he published his
independent discovery of the same law. William Thomson was a youth just
past his majority when he came to the aid of Joule before the British
Society, and but seven years older when he formulated his own doctrine of
the dissipation of energy. And Clausius and Rankine, who are usually
mentioned with Thomson as the great developers of thermo-dynamics, were
both far advanced with their novel studies before they were thirty. With
such a list in mind, we may well agree with the father of inductive science
that "the man who is young in years may be old in hours."
Yet we must not forget that the shield has a reverse side. For was not the
greatest of observing astronomers, Herschel, past thirty-five before he ever
saw a telescope, and past fifty before he discovered the heat rays of the
spectrum? And had not Faraday reached middle life before he turned his
attention especially to electricity? Clearly, then, to make this phrase
complete, Bacon should have added that "the man who is old in years may
be young in imagination." Here, however, even more appropriate than in the
other case—more's the pity—would have been the application of his
qualifying clause: "but that happeneth rarely."
THE FINAL UNIFICATION
There are only a few great generalizations as yet thought out in any
single field of science. Naturally, then, after a great generalization has found
definitive expression, there is a period of lull before another forward move.
In the case of the doctrines of energy, the lull has lasted half a century.
Throughout this period, it is true, a multitude of workers have been delving
in the field, and to the casual observer it might seem as if their activity had
been boundless, while the practical applications of their ideas—as
exemplified, for example, in the telephone, phonograph, electric light, and
so on—have been little less than revolutionary. Yet the most competent of
living authorities, Lord Kelvin, could assert in 1895 that in fifty years he
had learned nothing new regarding the nature of energy.
This, however, must not be interpreted as meaning that the world has
stood still during these two generations. It means rather that the rank and
file have been moving forward along the road the leaders had already
travelled. Only a few men in the world had the range of thought regarding
the new doctrine of energy that Lord Kelvin had at the middle of the
century. The few leaders then saw clearly enough that if one form of energy

is in reality merely an undulation or vibration among the particles of
"ponderable" matter or of ether, all other manifestations of energy must be
of the same nature. But the rank and file were not even within sight of this
truth for a long time after they had partly grasped the meaning of the
doctrine of conservation. When, late in the fifties, that marvellous young
Scotchman, James Clerk-Maxwell, formulating in other words an idea of
Faraday's, expressed his belief that electricity and magnetism are but
manifestations of various conditions of stress and motion in the ethereal
medium (electricity a displacement of strain, magnetism a whirl in the
ether), the idea met with no immediate popularity. And even less cordial
was the reception given the same thinker's theory, put forward in 1863, that
the ethereal undulations producing the phenomenon we call light differ in
no respect except in their wave-length from the pulsations of electro-
magnetism.
At about the same time Helmholtz formulated a somewhat similar
electro-magnetic theory of light; but even the weight of this combined
authority could not give the doctrine vogue until very recently, when the
experiments of Heinrich Hertz, the pupil of Helmholtz, have shown that a
condition of electrical strain may be developed into a wave system by
recurrent interruptions of the electric state in the generator, and that such
waves travel through the ether with the rapidity of light. Since then the
electro-magnetic theory of light has been enthusiastically referred to as the
greatest generalization of the century; but the sober thinker must see that it
is really only what Hertz himself called it—one pier beneath the great arch
of conservation. It is an interesting detail of the architecture, but the part
cannot equal the size of the whole.
More than that, this particular pier is as yet by no means a very firm one.
It has, indeed, been demonstrated that waves of electro-magnetism pass
through space with the speed of light, but as yet no one has developed
electric waves even remotely approximating the shortness of the visual rays.
The most that can positively be asserted, therefore, is that all the known
forms of radiant energy-heat, light, electro-magnetism—travel through
space at the same rate of speed, and consist of traverse vibrations—"lateral
quivers," as Fresnel said of light—known to differ in length, and not
positively known to differ otherwise. It has, indeed, been suggested that the
newest form of radiant energy, the famous X-ray of Professor Roentgen's
discovery, is a longitudinal vibration, but this is a mere surmise. Be that as

it may, there is no one now to question that all forms of radiant energy,
whatever their exact affinities, consist essentially of undulatory motions of
one uniform medium.
A full century of experiment, calculation, and controversy has thus
sufficed to correlate the "imponderable fluids" of our forebears, and reduce
them all to manifestations of motion among particles of matter. At first
glimpse that seems an enormous change of view. And yet, when closely
considered, that change in thought is not so radical as the change in phrase
might seem to imply. For the nineteenth-century physicist, in displacing the
"imponderable fluids" of many kinds—one each for light, heat, electricity,
magnetism—has been obliged to substitute for them one all-pervading
fluid, whose various quivers, waves, ripples, whirls or strains produce the
manifestations which in popular parlance are termed forms of force. This
all-pervading fluid the physicist terms the ether, and he thinks of it as
having no weight. In effect, then, the physicist has dispossessed the many
imponderables in favor of a single imponderable—though the word
imponderable has been banished from his vocabulary. In this view the ether
—which, considered as a recognized scientific verity, is essentially a
nineteenth-century discovery—is about the most interesting thing in the
universe. Something more as to its properties, real or assumed, we shall
have occasion to examine as we turn to the obverse side of physics, which
demands our attention in the next chapter.

IX. THE ETHER AND PONDERABLE
MATTER
"Whatever difficulties we may have in forming a consistent idea of the
constitution of the ether, there can be no doubt that the interplanetary and
interstellar spaces are not empty, but are occupied by a material substance
or body which is certainly the largest and probably the most uniform body
of which we have any knowledge."
Such was the verdict pronounced some thirty years ago by James Clerk-
Maxwell, one of the very greatest of nineteenth-century physicists,
regarding the existence of an all-pervading plenum in the universe, in which
every particle of tangible matter is immersed. And this verdict may be said
to express the attitude of the entire philosophical world of our day. Without
exception, the authoritative physicists of our time accept this plenum as a
verity, and reason about it with something of the same confidence they
manifest in speaking of "ponderable" matter or of, energy. It is true there are
those among them who are disposed to deny that this all-pervading plenum
merits the name of matter. But that it is a something, and a vastly important
something at that, all are agreed. Without it, they allege, we should know
nothing of light, of radiant heat, of electricity or magnetism; without it there
would probably be no such thing as gravitation; nay, they even hint that
without this strange something, ether, there would be no such thing as
matter in the universe. If these contentions of the modern physicist are
justified, then this intangible ether is incomparably the most important as
well as the "largest and most uniform substance or body" in the universe. Its
discovery may well be looked upon as one of the most important feats of
the nineteenth century.
For a discovery of that century it surely is, in the sense that all the known
evidences of its existence were gathered in that epoch. True dreamers of all
ages have, for metaphysical reasons, imagined the existence of intangible
fluids in space—they had, indeed, peopled space several times over with
different kinds of ethers, as Maxwell remarks—but such vague dreamings
no more constituted the discovery of the modern ether than the dream of

some pre-Columbian visionary that land might lie beyond the unknown
waters constituted the discovery of America. In justice it must be admitted
that Huyghens, the seventeenth-century originator of the undulatory theory
of light, caught a glimpse of the true ether; but his contemporaries and some
eight generations of his successors were utterly deaf to his claims; so he
bears practically the same relation to the nineteenth-century discoverers of
ether that the Norseman bears to Columbus.
The true Columbus of the ether was Thomas Young. His discovery was
consummated in the early days of the nineteenth century, when he brought
forward the first, conclusive proofs of the undulatory theory of light. To say
that light consists of undulations is to postulate something that undulates;
and this something could not be air, for air exists only in infinitesimal
quantity, if at all, in the interstellar spaces, through which light freely
penetrates. But if not air, what then? Why, clearly, something more
intangible than air; something supersensible, evading all direct efforts to
detect it, yet existing everywhere in seemingly vacant space, and also
interpenetrating the substance of all transparent liquids and solids, if not,
indeed, of all tangible substances. This intangible something Young
rechristened the Luminiferous Ether.
In the early days of his discovery Young thought of the undulations
which produce light and radiant heat as being longitudinal—a forward and
backward pulsation, corresponding to the pulsations of sound—and as such
pulsations can be transmitted by a fluid medium with the properties of
ordinary fluids, he was justified in thinking of the ether as being like a fluid
in its properties, except for its extreme intangibility. But about 1818 the
experiments of Fresnel and Arago with polarization of light made it seem
very doubtful whether the theory of longitudinal vibrations is sufficient, and
it was suggested by Young, and independently conceived and demonstrated
by Fresnel, that the luminiferous undulations are not longitudinal, but
transverse; and all the more recent experiments have tended to confirm this
view. But it happens that ordinary fluids—gases and liquids—cannot
transmit lateral vibrations; only rigid bodies are capable of such a vibration.
So it became necessary to assume that the luminiferous ether is a body
possessing elastic rigidity—a familiar property of tangible solids, but one
quite unknown among fluids.

The idea of transverse vibrations carried with it another puzzle. Why
does not the ether, when set aquiver with the vibration which gives us the
sensation we call light, have produced in its substance subordinate quivers,
setting out at right angles from the path of the original quiver? Such
perpendicular vibrations seem not to exist, else we might see around a
corner; how explain their absence? The physicist could think of but one
way: they must assume that the ether is incompressible. It must fill all space
—at any rate, all space with which human knowledge deals—perfectly full.
These properties of the ether, incompressibility and elastic rigidity, are
quite conceivable by themselves; but difficulties of thought appear when we
reflect upon another quality which the ether clearly must possess—namely,
frictionlessness. By hypothesis this rigid, incompressible body pervades all
space, imbedding every particle of tangible matter; yet it seems not to retard
the movements of this matter in the slightest degree. This is undoubtedly
the most difficult to comprehend of the alleged properties of the ether. The
physicist explains it as due to the perfect elasticity of the ether, in virtue of
which it closes in behind a moving particle with a push exactly
counterbalancing the stress required to penetrate it in front.
To a person unaccustomed to think of seemingly solid matter as really
composed of particles relatively wide apart, it is hard to understand the
claim that ether penetrates the substance of solids—of glass, for example—
and, to use Young's expression, which we have previously quoted, moves
among them as freely as the wind moves through a grove of trees. This
thought, however, presents few difficulties to the mind accustomed to
philosophical speculation. But the question early arose in the mind of
Fresnel whether the ether is not considerably affected by contact with the
particles of solids. Some of his experiments led him to believe that a portion
of the ether which penetrates among the molecules of tangible matter is
held captive, so to speak, and made to move along with these particles. He
spoke of such portions of the ether as "bound" ether, in contradistinction to
the great mass of "free" ether. Half a century after Fresnel's death, when the
ether hypothesis had become an accepted tenet of science, experiments
were undertaken by Fizeau in France, and by Clerk-Maxwell in England, to
ascertain whether any portion of ether is really thus bound to particles of
matter; but the results of the experiments were negative, and the question is
still undetermined.

While the undulatory theory of light was still fighting its way, another
kind of evidence favoring the existence of an ether was put forward by
Michael Faraday, who, in the course of his experiments in electrical and
magnetic induction, was led more and more to perceive definite lines or
channels of force in the medium subject to electro-magnetic influence.
Faraday's mind, like that of Newton and many other philosophers, rejected
the idea of action at a distance, and he felt convinced that the phenomena of
magnetism and of electric induction told strongly for the existence of an
invisible plenum everywhere in space, which might very probably be the
same plenum that carries the undulations of light and radiant heat.
Then, about the middle of the century, came that final revolution of
thought regarding the nature of energy which we have already outlined in
the preceding chapter, and with that the case for ether was considered to be
fully established. The idea that energy is merely a "mode of motion" (to
adopt Tyndall's familiar phrase), combined with the universal rejection of
the notion of action at a distance, made the acceptance of a plenum
throughout space a necessity of thought—so, at any rate, it has seemed to
most physicists of recent decades. The proof that all known forms of radiant
energy move through space at the same rate of speed is regarded as
practically a demonstration that but one plenum—one ether—is concerned
in their transmission. It has, indeed, been tentatively suggested, by
Professor J. Oliver Lodge, that there may be two ethers, representing the
two opposite kinds of electricity, but even the author of this hypothesis
would hardly claim for it a high degree of probability.
The most recent speculations regarding the properties of the ether have
departed but little from the early ideas of Young and Fresnel. It is assumed
on all sides that the ether is a continuous, incompressible body, possessing
rigidity and elasticity. Lord Kelvin has even calculated the probable density
of this ether, and its coefficient of rigidity. As might be supposed, it is all
but infinitely tenuous as compared with any tangible solid, and its rigidity is
but infinitesimal as compared with that of steel. In a word, it combines
properties of tangible matter in a way not known in any tangible substance.
Therefore we cannot possibly conceive its true condition correctly. The
nearest approximation, according to Lord Kelvin, is furnished by a mould
of transparent jelly. It is a crude, inaccurate analogy, of course, the density
and resistance of jelly in particular being utterly different from those of the
ether; but the quivers that run through the jelly when it is shaken, and the

elastic tension under which it is placed when its mass is twisted about,
furnish some analogy to the quivers and strains in the ether, which are held
to constitute radiant energy, magnetism, and electricity.
The great physicists of the day being at one regarding the existence of
this all-pervading ether, it would be a manifest presumption for any one
standing without the pale to challenge so firmly rooted a belief. And,
indeed, in any event, there seems little ground on which to base such a
challenge. Yet it may not be altogether amiss to reflect that the physicist of
to-day is no more certain of his ether than was his predecessor of the
eighteenth century of the existence of certain alleged substances which he
called phlogiston, caloric, corpuscles of light, and magnetic and electric
fluids. It would be but the repetition of history should it chance that before
the close of another century the ether should have taken its place along with
these discarded creations of the scientific imagination of earlier generations.
The philosopher of to-day feels very sure that an ether exists; but when he
says there is "no doubt" of its existence he speaks incautiously, and steps
beyond the bounds of demonstration. He does not KNOW that action
cannot take place at a distance; he does not KNOW that empty space itself
may not perform the functions which he ascribes to his space-filling ether.
Meantime, however, the ether, be it substance or be it only dream-stuff, is
serving an admirable purpose in furnishing a fulcrum for modern physics.
Not alone to the student of energy has it proved invaluable, but to the
student of matter itself as well. Out of its hypothetical mistiness has been
reared the most tenable theory of the constitution of ponderable matter
which has yet been suggested—or, at any rate, the one that will stand as the
definitive nineteenth-century guess at this "riddle of the ages." I mean, of
course, the vortex theory of atoms—that profound and fascinating doctrine
which suggests that matter, in all its multiform phases, is neither more nor
less than ether in motion.
The author of this wonderful conception is Lord Kelvin. The idea was
born in his mind of a happy union of mathematical calculations with
concrete experiments. The mathematical calculations were largely the work
of Hermann von Helmholtz, who, about the year 1858, had undertaken to
solve some unique problems in vortex motions. Helmholtz found that a
vortex whirl, once established in a frictionless medium, must go on,
theoretically, unchanged forever. In a limited medium such a whirl may be

V-shaped, with its ends at the surface of the medium. We may imitate such a
vortex by drawing the bowl of a spoon quickly through a cup of water. But
in a limitless medium the vortex whirl must always be a closed ring, which
may take the simple form of a hoop or circle, or which may be indefinitely
contorted, looped, or, so to speak, knotted. Whether simple or contorted,
this endless chain of whirling matter (the particles revolving about the axis
of the loop as the particles of a string revolve when the string is rolled
between the fingers) must, in a frictionless medium, retain its form and
whirl on with undiminished speed forever.
While these theoretical calculations of Helmholtz were fresh in his mind,
Lord Kelvin (then Sir William Thomson) was shown by Professor P. G.
Tait, of Edinburgh, an apparatus constructed for the purpose of creating
vortex rings in air. The apparatus, which any one may duplicate, consisted
simply of a box with a hole bored in one side, and a piece of canvas
stretched across the opposite side in lieu of boards. Fumes of chloride of
ammonia are generated within the box, merely to render the air visible. By
tapping with the band on the canvas side of the box, vortex rings of the
clouded air are driven out, precisely similar in appearance to those smoke-
rings which some expert tobacco-smokers can produce by tapping on their
cheeks, or to those larger ones which we sometimes see blown out from the
funnel of a locomotive.
The advantage of Professor Tait's apparatus is its manageableness and the
certainty with which the desired result can be produced. Before Lord
Kelvin's interested observation it threw out rings of various sizes, which
moved straight across the room at varying rates of speed, according to the
initial impulse, and which behaved very strangely when coming in contact
with one another. If, for example, a rapidly moving ring overtook another
moving in the same path, the one in advance seemed to pause, and to spread
out its periphery like an elastic band, while the pursuer seemed to contract,
till it actually slid through the orifice of the other, after which each ring
resumed its original size, and continued its course as if nothing had
happened. When, on the other hand, two rings moving in slightly different
directions came near each other, they seemed to have an attraction for each
other; yet if they impinged, they bounded away, quivering like elastic
solids. If an effort were made to grasp or to cut one of these rings, the subtle
thing shrank from the contact, and slipped away as if it were alive.

And all the while the body which thus conducted itself consisted simply
of a whirl in the air, made visible, but not otherwise influenced, by smoky
fumes. Presently the friction of the surrounding air wore the ring away, and
it faded into the general atmosphere—often, however, not until it had
persisted for many seconds, and passed clear across a large room. Clearly, if
there were no friction, the ring's inertia must make it a permanent structure.
Only the frictionless medium was lacking to fulfil all the conditions of
Helmholtz's indestructible vortices. And at once Lord Kelvin bethought him
of the frictionless medium which physicists had now begun to accept—the
all-pervading ether. What if vortex rings were started in this ether, must
they not have the properties which the vortex rings in air had exhibited—
inertia, attraction, elasticity? And are not these the properties of ordinary
tangible matter? Is it not probable, then, that what we call matter consists
merely of aggregations of infinitesimal vortex rings in the ether?
Thus the vortex theory of atoms took form in Lord Kelvin's mind, and its
expression gave the world what many philosophers of our time regard as
the most plausible conception of the constitution of matter hitherto
formulated. It is only a theory, to be sure; its author would be the last person
to claim finality for it. "It is only a dream," Lord Kelvin said to me, in
referring to it not long ago. But it has a basis in mathematical calculation
and in analogical experiment such as no other theory of matter can lay
claim to, and it has a unifying or monistic tendency that makes it, for the
philosophical mind, little less than fascinating. True or false, it is the
definitive theory of matter of the twentieth century.
Quite aside from the question of the exact constitution of the ultimate
particles of matter, questions as to the distribution of such particles, their
mutual relations, properties, and actions, came in for a full share of
attention during the nineteenth century, though the foundations for the
modern speculations were furnished in a previous epoch. The most popular
eighteenth-century speculation as to the ultimate constitution of matter was
that of the learned Italian priest, Roger Joseph Boscovich, published in
1758, in his Theoria Philosophiae Naturalis. "In this theory," according to
an early commentator, "the whole mass of which the bodies of the universe
are composed is supposed to consist of an exceedingly great yet finite
number of simple, indivisible, inextended atoms. These atoms are endued
by the Creator with REPULSIVE and ATTRACTIVE forces, which vary
according to the distance. At very small distances the particles of matter

repel each other; and this repulsive force increases beyond all limits as the
distances are diminished, and will consequently forever prevent actual
contact. When the particles of matter are removed to sensible distances, the
repulsive is exchanged for an attractive force, which decreases in inverse
ratio with the squares of the distances, and extends beyond the spheres of
the most remote comets."
This conception of the atom as a mere centre of force was hardly such as
could satisfy any mind other than the metaphysical. No one made a
conspicuous attempt to improve upon the idea, however, till just at the close
of the century, when Humphry Davy was led, in the course of his studies of
heat, to speculate as to the changes that occur in the intimate substance of
matter under altered conditions of temperature. Davy, as we have seen,
regarded heat as a manifestation of motion among the particles of matter. As
all bodies with which we come in contact have some temperature, Davy
inferred that the intimate particles of every substance must be perpetually in
a state of vibration. Such vibrations, he believed, produced the "repulsive
force" which (in common with Boscovich) he admitted as holding the
particles of matter at a distance from one another. To heat a substance
means merely to increase the rate of vibration of its particles; thus also,
plainly, increasing the repulsive forces and expanding the bulk of the mass
as a whole. If the degree of heat applied be sufficient, the repulsive force
may become strong enough quite to overcome the attractive force, and the
particles will separate and tend to fly away from one another, the solid then
becoming a gas.
Not much attention was paid to these very suggestive ideas of Davy,
because they were founded on the idea that heat is merely a motion, which
the scientific world then repudiated; but half a century later, when the new
theories of energy had made their way, there came a revival of practically
the same ideas of the particles of matter (molecules they were now called)
which Davy had advocated. Then it was that Clausius in Germany and
Clerk-Maxwell in England took up the investigation of what came to be
known as the kinetic theory of gases—the now familiar conception that all
the phenomena of gases are due to the helter-skelter flight of the showers of
widely separated molecules of which they are composed. The specific idea
that the pressure or "spring" of gases is due to such molecular impacts was
due to Daniel Bournelli, who advanced it early in the eighteenth century.
The idea, then little noticed, had been revived about a century later by

William Herapath, and again with some success by J. J. Waterston, of
Bombay, about 1846; but it gained no distinct footing until taken in hand by
Clausius in 1857 and by Clerk-Maxwell in 1859.
The considerations that led Clerk-Maxwell to take up the computations
may be stated in his own words, as formulated in a paper "On the Motions
and Collisions of Perfectly Elastic Spheres."
"So many of the properties of matter, especially when in the gaseous
form," he says, "can be deduced from the hypothesis that their minute parts
are in rapid motion, the velocity increasing with the temperature, that the
precise nature of this motion becomes a subject of rational curiosity. Daniel
Bournelli, Herapath, Joule, Kronig, Clausius, etc., have shown that the
relations between pressure, temperature, and density in a perfect gas can be
explained by supposing the particles to move with uniform velocities in
straight lines, striking against the sides of the containing vessel and thus
producing pressure. It is not necessary to suppose each particle to travel to
any great distance in the same straight line; for the effect in producing
pressure will be the same if the particles strike against each other; so that
the straight line described may be very short. M. Clausius has determined
the mean length of path in terms of the average of the particles, and the
distance between the centres of two particles when the collision takes place.
We have at present no means of ascertaining either of these distances; but
certain phenomena, such as the internal friction of gases, the conduction of
heat through a gas, and the diffusion of one gas through another, seem to
indicate the possibility of determining accurately the mean length of path
which a particle describes between two successive collisions. In order to lay
the foundation of such investigations on strict mechanical principles, I shall
demonstrate the laws of motion of an indefinite number of small, hard, and
perfectly elastic spheres acting on one another only during impact. If the
properties of such a system of bodies are found to correspond to those of
gases, an important physical analogy will be established, which may lead to
more accurate knowledge of the properties of matter. If experiments on
gases are inconsistent with the hypothesis of these propositions, then our
theory, though consistent with itself, is proved to be incapable of explaining
the phenomena of gases. In either case it is necessary to follow out these
consequences of the hypothesis.

"Instead of saying that the particles are hard, spherical, and elastic, we
may, if we please, say the particles are centres of force, of which the action
is insensible except at a certain very small distance, when it suddenly
appears as a repulsive force of very great intensity. It is evident that either
assumption will lead to the same results. For the sake of avoiding the
repetition of a long phrase about these repulsive bodies, I shall proceed
upon the assumption of perfectly elastic spherical bodies. If we suppose
those aggregate molecules which move together to have a bounding surface
which is not spherical, then the rotatory motion of the system will close up
a certain proportion of the whole vis viva, as has been shown by Clausius,
and in this way we may account for the value of the specific heat being
greater than on the more simple hypothesis."(1)
The elaborate investigations of Clerk-Maxwell served not merely to
substantiate the doctrine, but threw a flood of light upon the entire subject
of molecular dynamics. Soon the physicists came to feel as certain of the
existence of these showers of flying molecules making up a gas as if they
could actually see and watch their individual actions. Through study of the
viscosity of gases—that is to say, of the degree of frictional opposition they
show to an object moving through them or to another current of gas—an
idea was gained, with the aid of mathematics, of the rate of speed at which
the particles of the gas are moving, and the number of collisions which each
particle must experience in a given time, and of the length of the average
free path traversed by the molecule between collisions, These
measurements were confirmed by study of the rate of diffusion at which
different gases mix together, and also by the rate of diffusion of heat
through a gas, both these phenomena being chiefly due to the helter-skelter
flight of the molecules.
It is sufficiently astonishing to be told that such measurements as these
have been made at all, but the astonishment grows when one hears the
results. It appears from Clerk-Maxwell's calculations that the mean free
path, or distance traversed by the molecules between collisions in ordinary
air, is about one-half-millionth of an inch; while the speed of the molecules
is such that each one experiences about eight billions of collisions per
second! It would be hard, perhaps, to cite an illustration showing the
refinements of modern physics better than this; unless, indeed, one other
result that followed directly from these calculations be considered such—
the feat, namely, of measuring the size of the molecules themselves.

Clausius was the first to point out how this might be done from a
knowledge of the length of free path; and the calculations were made by
Loschmidt in Germany and by Lord Kelvin in England, independently.
The work is purely mathematical, of course, but the results are regarded
as unassailable; indeed, Lord Kelvin speaks of them as being absolutely
demonstrative within certain limits of accuracy. This does not mean,
however, that they show the exact dimensions of the molecule; it means an
estimate of the limits of size within which the actual size of the molecule
may lie. These limits, Lord Kelvin estimates, are about the one-ten-
millionth of a centimetre for the maximum, and the one-one-hundred-
millionth of a centimetre for the minimum. Such figures convey no
particular meaning to our blunt senses, but Lord Kelvin has given a tangible
illustration that aids the imagination to at least a vague comprehension of
the unthinkable smallness of the molecule. He estimates that if a ball, say of
water or glass, about "as large as a football, were to be magnified up to the
size of the earth, each constituent molecule being magnified in the same
proportion, the magnified structure would be more coarse-grained than a
heap of shot, but probably less coarse-grained than a heap of footballs."
Several other methods have been employed to estimate the size of
molecules. One of these is based upon the phenomena of contact electricity;
another upon the wave-theory of light; and another upon capillary
attraction, as shown in the tense film of a soap-bubble! No one of these
methods gives results more definite than that due to the kinetic theory of
gases, just outlined; but the important thing is that the results obtained by
these different methods (all of them due to Lord Kelvin) agree with one
another in fixing the dimensions of the molecule at somewhere about the
limits already mentioned. We may feel very sure indeed, therefore, that the
molecules of matter are not the unextended, formless points which
Boscovich and his followers of the eighteenth century thought them. But all
this, it must be borne in mind, refers to the molecule, not to the ultimate
particle of matter, about which we shall have more to say in another
connection. Curiously enough, we shall find that the latest theories as to the
final term of the series are not so very far afield from the dreamings of the
eighteenth-century philosophers; the electron of J. J. Thompson shows
many points of resemblance to the formless centre of Boscovich.

Whatever the exact form of the molecule, its outline is subject to
incessant variation; for nothing in molecular science is regarded as more
firmly established than that the molecule, under all ordinary circumstances,
is in a state of intense but variable vibration. The entire energy of a
molecule of gas, for example, is not measured by its momentum, but by this
plus its energy of vibration and rotation, due to the collisions already
referred to. Clausius has even estimated the relative importance of these
two quantities, showing that the translational motion of a molecule of gas
accounts for only three-fifths of its kinetic energy. The total energy of the
molecule (which we call "heat") includes also another factor—namely,
potential energy, or energy of position, due to the work that has been done
on expanding, in overcoming external pressure, and internal attraction
between the molecules themselves. This potential energy (which will be
recovered when the gas contracts) is the "latent heat" of Black, which so
long puzzled the philosophers. It is latent in the same sense that the energy
of a ball thrown into the air is latent at the moment when the ball poises at
its greatest height before beginning to fall.
It thus appears that a variety of motions, real and potential, enter into the
production of the condition we term heat. It is, however, chiefly the
translational motion which is measurable as temperature; and this, too,
which most obviously determines the physical state of the substance that the
molecules collectively compose—whether, that is to say, it shall appear to
our blunt perceptions as a gas, a liquid, or a solid. In the gaseous state, as
we have seen, the translational motion of the molecules is relatively
enormous, the molecules being widely separated. It does not follow, as we
formerly supposed, that this is evidence of a repulsive power acting
between the molecules. The physicists of to-day, headed by Lord Kelvin,
decline to recognize any such power. They hold that the molecules of a gas
fly in straight lines by virtue of their inertia, quite independently of one
another, except at times of collision, from which they rebound by virtue of
their elasticity; or on an approach to collision, in which latter case, coming
within the range of mutual attraction, two molecules may circle about each
other, as a comet circles about the sun, then rush apart again, as the comet
rushes from the sun.
It is obvious that the length of the mean free path of the molecules of a
gas may be increased indefinitely by decreasing the number of the
molecules themselves in a circumscribed space. It has been shown by

Professors Tait and Dewar that a vacuum may be produced artificially of
such a degree of rarefaction that the mean free path of the remaining
molecules is measurable in inches. The calculation is based on experiments
made with the radiometer of Professor Crookes, an instrument which in
itself is held to demonstrate the truth of the kinetic theory of gases. Such an
attenuated gas as this is considered by Professor Crookes as constituting a
fourth state of matter, which he terms ultra-gaseous.
If, on the other hand, a gas is subjected to pressure, its molecules are
crowded closer together, and the length of their mean free path is thus
lessened. Ultimately, the pressure being sufficient, the molecules are
practically in continuous contact. Meantime the enormously increased
number of collisions has set the molecules more and more actively
vibrating, and the temperature of the gas has increased, as, indeed,
necessarily results in accordance with the law of the conservation of energy.
No amount of pressure, therefore, can suffice by itself to reduce the gas to a
liquid state. It is believed that even at the centre of the sun, where the
pressure is almost inconceivably great, all matter is to be regarded as really
gaseous, though the molecules must be so packed together that the
consistency is probably more like that of a solid.
If, however, coincidently with the application of pressure, opportunity be
given for the excess of heat to be dissipated to a colder surrounding
medium, the molecules, giving off their excess of energy, become relatively
quiescent, and at a certain stage the gas becomes a liquid. The exact point at
which this transformation occurs, however, differs enormously for different
substances. In the case of water, for example, it is a temperature more than
four hundred degrees above zero, centigrade; while for atmospheric air it is
one hundred and ninety-four degrees centigrade below zero, or more than a
hundred and fifty degrees below the point at which mercury freezes.
Be it high or low, the temperature above which any substance is always a
gas, regardless of pressure, is called the critical temperature, or absolute
boiling-point, of that substance. It does not follow, however, that below this
point the substance is necessarily a liquid. This is a matter that will be
determined by external conditions of pressure. Even far below the critical
temperature the molecules have an enormous degree of activity, and tend to
fly asunder, maintaining what appears to be a gaseous, but what technically
is called a vaporous, condition—the distinction being that pressure alone

suffices to reduce the vapor to the liquid state. Thus water may change from
the gaseous to the liquid state at four hundred degrees above zero, but under
conditions of ordinary atmospheric pressure it does not do so until the
temperature is lowered three hundred degrees further. Below four hundred
degrees, however, it is technically a vapor, not a gas; but the sole difference,
it will be understood, is in the degree of molecular activity.
It thus appeared that the prevalence of water in a vaporous and liquid
rather than in a "permanently" gaseous condition here on the globe is a
mere incident of telluric evolution. Equally incidental is the fact that the air
we breathe is "permanently" gaseous and not liquid or solid, as it might be
were the earth's surface temperature to be lowered to a degree which, in the
larger view, may be regarded as trifling. Between the atmospheric
temperature in tropical and in arctic regions there is often a variation of
more than one hundred degrees; were the temperature reduced another
hundred, the point would be reached at which oxygen gas becomes a vapor,
and under increased pressure would be a liquid. Thirty-seven degrees more
would bring us to the critical temperature of nitrogen.
Nor is this a mere theoretical assumption; it is a determination of
experimental science, quite independent of theory. The physicist in the
laboratory has produced artificial conditions of temperature enabling him to
change the state of the most persistent gases. Some fifty years since, when
the kinetic theory was in its infancy, Faraday liquefied carbonic-acid gas,
among others, and the experiments thus inaugurated have been extended by
numerous more recent investigators, notably by Cailletet in Switzerland, by
Pictet in France, and by Dr. Thomas. Andrews and Professor James Dewar
in England. In the course of these experiments not only has air been
liquefied, but hydrogen also, the most subtle of gases; and it has been made
more and more apparent that gas and liquid are, as Andrews long ago
asserted, "only distant stages of a long series of continuous physical
changes." Of course, if the temperature be lowered still further, the liquid
becomes a solid; and this change also has been effected in the case of some
of the most "permanent" gases, including air.
The degree of cold—that is, of absence of heat—thus produced is
enormous, relatively to anything of which we have experience in nature
here at the earth now, yet the molecules of solidified air, for example, are
not absolutely quiescent. In other words, they still have a temperature,

though so very low. But it is clearly conceivable that a stage might be
reached at which the molecules became absolutely quiescent, as regards
either translational or vibratory motion. Such a heatless condition has been
approached, but as yet not quite attained, in laboratory experiments. It is
called the absolute zero of temperature, and is estimated to be equivalent to
two hundred and seventy-three degrees Centigrade below the freezing-point
of water, or ordinary zero.
A temperature (or absence of temperature) closely approximating this is
believed to obtain in the ethereal ocean of interplanetary and interstellar
space, which transmits, but is thought not to absorb, radiant energy. We here
on the earth's surface are protected from exposure to this cold, which would
deprive every organic thing of life almost instantaneously, solely by the thin
blanket of atmosphere with which the globe is coated. It would seem as if
this atmosphere, exposed to such a temperature at its surface, must there be
incessantly liquefied, and thus fall back like rain to be dissolved into gas
again while it still is many miles above the earth's surface. This may be the
reason why its scurrying molecules have not long ago wandered off into
space and left the world without protection.
But whether or not such liquefaction of the air now occurs in our outer
atmosphere, there can be no question as to what must occur in its entire
depth were we permanently shut off from the heating influence of the sun,
as the astronomers threaten that we may be in a future age. Each molecule,
not alone of the atmosphere, but of the entire earth's substance, is kept
aquiver by the energy which it receives, or has received, directly or
indirectly, from the sun. Left to itself, each molecule would wear out its
energy and fritter it off into the space about it, ultimately running
completely down, as surely as any human-made machine whose power is
not from time to time restored. If, then, it shall come to pass in some future
age that the sun's rays fail us, the temperature of the globe must gradually
sink towards the absolute zero. That is to say, the molecules of gas which
now fly about at such inconceivable speed must drop helpless to the earth;
liquids must in turn become solids; and solids themselves, their molecular
quivers utterly stilled, may perhaps take on properties the nature of which
we cannot surmise.
Yet even then, according to the current hypothesis, the heatless molecule
will still be a thing instinct with life. Its vortex whirl will still go on,

uninfluenced by the dying-out of those subordinate quivers that produced
the transitory effect which we call temperature. For those transitory thrills,
though determining the physical state of matter as measured by our crude
organs of sense, were no more than non-essential incidents; but the vortex
whirl is the essence of matter itself. Some estimates as to the exact
character of this intramolecular motion, together with recent theories as to
the actual structure of the molecule, will claim our attention in a later
volume. We shall also have occasion in another connection to make fuller
inquiry as to the phenomena of low temperature.

APPENDIX
REFERENCE-LIST

CHAPTER I

THE SUCCESSORS OF NEWTON IN ASTRONOMY (1) (p. 10). An Account of Several
Extraordinary Meteors or Lights in the Sky, by Dr. Edmund Halley. Phil.
Trans. of Royal Society of London, vol. XXIX, pp. 159-162. Read before
the Royal Society in the autumn of 1714. (2) (p. 13). Phil. Trans. of
Royal Society of London for 1748, vol. XLV., pp. 8, 9. From A Letter to
the Right Honorable George, Earl of Macclesfield, concerning an Apparent
Motion observed in some of the Fixed Stars, by James Bradley, D.D.,
Astronomer Royal and F.R.S.

CHAPTER II

THE PROGRESS OF MODERN ASTRONOMY

(1) (p. 25). William Herschel, Phil. Trans. for 1783, vol. LXXIII. (2)
(p. 30). Kant's Cosmogony, ed. and trans. by W. Hartie, D.D., Glasgow,
900, pp. 74-81. (3) (p. 39). Exposition du systeme du monde (included in
oeuvres Completes), by M. le Marquis de Laplace, vol. VI., p. 498. (4)
(p. 48). From The Scientific Papers of J. Clerk-Maxwell, edited by W.
D. Nevin, M.A. (2 vols.), vol. I., pp. 372-374. This is a reprint of
Clerk-Maxwell's prize paper of 1859.

CHAPTER III

THE NEW SCIENCE OF PALEONTOLOGY

(1) (p. 81). Baron de Cuvier, Theory of the Earth, New York, 1818, p.
98. (2) (p. 88). Charles Lyell, Principles of Geology (4 vols.),
London, 1834. (p. 92). Ibid., vol. III., pp. 596-598. (4) (p. 100). Hugh
Falconer, in Paleontological Memoirs, vol. II., p. 596. (5) (p. 101).
Ibid., p. 598. (6) (p. 102). Ibid., p. 599. (7) (p. 111). Fossil Horses
in America (reprinted from American Naturalist, vol. VIII., May, 1874),
by O. C. Marsh, pp. 288, 289.

CHAPTER IV

THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY

(1) (p. 123). James Hutton, from Transactions of the Royal Society of
Edinburgh, 1788, vol. I., p. 214. A paper on the "Theory of the Earth,"
read before the Society in 1781. (2) (p. 128). Ibid., p. 216. (3)
(p. 139). Consideration on Volcanoes, by G. Poulett Scrope, Esq., pp.
228-234. (4) (p. 153). L. Agassiz, Etudes sur les glaciers, Neufchatel,
1840, p. 240.

CHAPTER V

THE NEW SCIENCE OF METEOROLOGY

(1) (p. 182). Theory of Rain, by James Hutton, in Transactions of the
Royal Society of Edinburgh, 1788, vol. 1, pp. 53-56. (2) (p. 191). Essay
on Dew, by W. C. Wells, M.D., F.R.S., London, 1818, pp. 124 f.

CHAPTER VI

MODERN THEORIES OF HEAT AND LIGHT

(1) (p. 215). Essays Political, Economical, and Philosophical, by
Benjamin Thompson, Count of Rumford (2 vols.), Vol. II., pp. 470-493,
London; T. Cadell, Jr., and W. Davies, 1797. (2) (p. 220). Thomas Young,
Phil. Trans., 1802, p. 35. (3) (p. 223). Ibid., p. 36.

CHAPTER VII

THE MODERN DEVELOPMENT OF ELECTRICITY AND MAGNETISM

(1) (p. 235). Davy's paper before Royal Institution, 1810. (2) (p. 238).
Hans Christian Oersted, Experiments with the Effects of the Electric
Current on the Magnetic Needle, 1815. (3) (p. 243). On the Induction
of Electric Currents, by Michael Faraday, F.R.S., Phil. Trans. of Royal
Society of London for 1832, pp. 126-128. (4) (p. 245). Explication of
Arago's Magnetic Phenomena, by Michael Faraday, F.R.S., Phil. Trans.
Royal Society of London for 1832, pp. 146-149.

CHAPTER VIII

THE CONSERVATION OF ENERGY

(1) (p. 267). The Forces of Inorganic Nature, a paper by Dr. Julius
Robert Mayer, Liebig's Annalen, 1842. (2) (p. 272). On the Calorific
Effects of Magneto-Electricity and the Mechanical Value of Heat, by J.
P. Joule, in Report of the British Association for the Advancement of
Science, vol. XII., p. 33.

CHAPTER IX

THE ETHER AND PONDERABLE MATTER

(1) (p. 297). James Clerk-Maxwell, Philosophical Magazine for January
and July, 1860.

END OF VOL. III

TABLE OF CONTENTS

FOR THE FIVE VOLUMES

BOOK I
I. PREHISTORIC SCIENCE
II. EGYPTIAN SCIENCE
III. SCIENCE OF BABYLONIA AND ASSYRIA
IV. THE DEVELOPMENT OF THE ALPHABET
V. THE BEGINNINGS OF GREEK SCIENCE
VI. THE EARLY GREEK PHILOSOPHERS IN ITALY
VII. GREEK SCIENCE IN THE EARLY ATTIC PERIOD
VIII. POST-SOCRATIC SCIENCE AT ATHENS—PLATO,
ARISTOTLE, AND THEOPHRASTUS
IX. GREEK SCIENCE OF THE ALEXANDRIAN OR HELLENISTIC
PERIOD
X. SCIENCE OF THE ROMAN PERIOD
XI. A RETROSPECTIVE GLANCE AT CLASSICAL SCIENCE

BOOK II. THE BEGINNINGS OF MODERN SCIENCE

I. SCIENCE IN THE DARK AGE
II. MEDIAEVAL SCIENCE AMONG THE ARABIANS
III. MEDIAEVAL SCIENCE IN THE WEST
IV. THE NEW COSMOLOGY—COPERNICUS TO KEPLER AND
GALILEO
V. GALILEO AND THE NEW PHYSICS
VI. TWO PSEUDO-SCIENCES—ALCHEMY AND ASTROLOGY
VII. FROM PARACELSUS TO HARVEY
VIII. MEDICINE IN THE SIXTEENTH AND SEVENTEENTH
CENTURIES
IX. PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF
LEARNING
X. THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE
XI. NEWTON AND THE COMPOSITION OF LIGHT
XII. NEWTON AND THE LAW OF GRAVITATION
XIII. INSTRUMENTS OF PRECISION IN THE AGE OF NEWTON
XIV. PROGRESS IN ELECTRICITY FROM GILBERT AND VON
GUERICKE TO FRANKLIN
XV. NATURAL HISTORY TO THE TIME OF LINNAEUS

BOOK III. MODERN DEVELOPMENT OF THE PHYSICAL
SCIENCES

I. THE SUCCESSORS OF NEWTON IN ASTRONOMY
II. THE PROGRESS OF MODERN ASTRONOMY
III. THE NEW SCIENCE OF PALEONTOLOGY
IV. THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY
V. THE NEW SCIENCE OF METEOROLOGY
VI. MODERN THEORIES OF HEAT AND LIGHT
VII. THE MODERN DEVELOPMENT OF ELECTRICITY AND
MAGNETISM
VIII. THE CONSERVATION OF ENERGY
IX. THE ETHER AND PONDERABLE MATTER

BOOK IV. MODERN DEVELOPMENT OF THE CHEMICAL AND
BIOLOGICAL SCIENCES
I. THE PHLOGISTON THEORY IN CHEMISTRY
II. THE BEGINNINGS OF MODERN CHEMISTRY
III. CHEMISTRY SINCE THE TIME OF DALTON
IV. ANATOMY AND PHYSIOLOGY IN THE EIGHTEENTH
CENTURY
V. ANATOMY AND PHYSIOLOGY IN THE NINETEENTH
CENTURY
VI. THEORIES OF ORGANIC EVOLUTION
VII. EIGHTEENTH-CENTURY MEDICINE

VIII. NINETEENTH-CENTURY MEDICINE
IX. THE NEW SCIENCE OF EXPERIMENTAL PSYCHOLOGY
X. THE NEW SCIENCE OF ORIENTAL ARCHAEOLOGY

BOOK V. ASPECTS OF RECENT SCIENCE
I. THE BRITISH MUSEUM
II. THE ROYAL SOCIETY OF LONDON FOR IMPROVING
NATURAL KNOWLEDGE
III. THE ROYAL INSTITUTION AND THE LOW-TEMPERATURE
RESEARCHES
IV. SOME PHYSICAL LABORATORIES AND PHYSICAL
PROBLEMS
V. THE MARINE BIOLOGICAL LABORATORY AT NAPLES
VI. ERNST HAECKEL AND THE NEW ZOOLOGY
VII. SOME MEDICAL LABORATORIES AND MEDICAL
PROBLEMS
VII. SOME UNSOLVED SCIENTIFIC PROBLEMS
IX. RETROSPECT AND PROSPECT

*** END OF THE PROJECT GUTENBERG EBOOK A HISTORY OF
SCIENCE — VOLUME 3 ***

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