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Title: A History of Science — Volume 2

Author: Henry Smith Williams
Edward Huntington Williams

Release date: April 1, 1999 [eBook #1706]
Most recently updated: January 29, 2013

Language: English

Other information and formats: www.gutenberg.org/ebooks/1706

Credits: Produced by Charles Keller, and David Widger

*** START OF THE PROJECT GUTENBERG EBOOK A HISTORY OF
SCIENCE — VOLUME 2 ***

A HISTORY OF SCIENCE

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

ASSISTED BY EDWARD H. WILLIAMS, M.D.

IN FIVE VOLUMES

VOLUME II.

CONTENTS

A HISTORY OF 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

APPENDIX
CHAPTER I
CHAPTER III
CHAPTER IV
CHAPTER V
CHAPTER VI
CHAPTER VII
CHAPTER VIII

CHAPTER IX
CHAPTER X
CHAPTER XI
CHAPTER XII
CHAPTER XIV

A HISTORY OF SCIENCE

BOOK II. THE BEGINNINGS OF MODERN
SCIENCE
The studies of the present book cover the progress of science from the
close of the Roman period in the fifth century A.D. to about the middle of
the eighteenth century. In tracing the course of events through so long a
period, a difficulty becomes prominent which everywhere besets the
historian in less degree—a difficulty due to the conflict between the strictly
chronological and the topical method of treatment. We must hold as closely
as possible to the actual sequence of events, since, as already pointed out,
one discovery leads on to another. But, on the other hand, progressive steps
are taken contemporaneously in the various fields of science, and if we
were to attempt to introduce these in strict chronological order we should
lose all sense of topical continuity.
Our method has been to adopt a compromise, following the course of a
single science in each great epoch to a convenient stopping-point, and then
turning back to bring forward the story of another science. Thus, for
example, we tell the story of Copernicus and Galileo, bringing the record of
cosmical and mechanical progress down to about the middle of the
seventeenth century, before turning back to take up the physiological
progress of the fifteenth and sixteenth centuries. Once the latter stream is
entered, however, we follow it without interruption to the time of Harvey
and his contemporaries in the middle of the seventeenth century, where we
leave it to return to the field of mechanics as exploited by the successors of
Galileo, who were also the predecessors and contemporaries of Newton.
In general, it will aid the reader to recall that, so far as possible, we hold
always to the same sequences of topical treatment of contemporary events;
as a rule we treat first the cosmical, then the physical, then the biological
sciences. The same order of treatment will be held to in succeeding
volumes.
Several of the very greatest of scientific generalizations are developed in
the period covered by the present book: for example, the Copernican theory
of the solar system, the true doctrine of planetary motions, the laws of

motion, the theory of the circulation of the blood, and the Newtonian theory
of gravitation. The labors of the investigators of the early decades of the
eighteenth century, terminating with Franklin's discovery of the nature of
lightning and with the Linnaean classification of plants and animals, bring
us to the close of our second great epoch; or, to put it otherwise, to the
threshold of the modern period.

I. SCIENCE IN THE DARK AGE
An obvious distinction between the classical and mediaeval epochs may
be found in the fact that the former produced, whereas the latter failed to
produce, a few great thinkers in each generation who were imbued with that
scepticism which is the foundation of the investigating spirit; who thought
for themselves and supplied more or less rational explanations of observed
phenomena. Could we eliminate the work of some score or so of classical
observers and thinkers, the classical epoch would seem as much a dark age
as does the epoch that succeeded it.
But immediately we are met with the question: Why do no great original
investigators appear during all these later centuries? We have already
offered a part explanation in the fact that the borders of civilization, where
racial mingling naturally took place, were peopled with semi-barbarians.
But we must not forget that in the centres of civilization all along there were
many men of powerful intellect. Indeed, it would violate the principle of
historical continuity to suppose that there was any sudden change in the
level of mentality of the Roman world at the close of the classical period.
We must assume, then, that the direction in which the great minds turned
was for some reason changed. Newton is said to have alleged that he made
his discoveries by "intending" his mind in a certain direction continuously.
It is probable that the same explanation may be given of almost every great
scientific discovery. Anaxagoras could not have thought out the theory of
the moon's phases; Aristarchus could not have found out the true
mechanism of the solar system; Eratosthenes could not have developed his
plan for measuring the earth, had not each of these investigators "intended"
his mind persistently towards the problems in question.
Nor can we doubt that men lived in every generation of the dark age who
were capable of creative thought in the field of science, bad they chosen
similarly to "intend" their minds in the right direction. The difficulty was
that they did not so choose. Their minds had a quite different bent. They
were under the spell of different ideals; all their mental efforts were directed
into different channels. What these different channels were cannot be in
doubt—they were the channels of oriental ecclesiasticism. One all-

significant fact speaks volumes here. It is the fact that, as Professor
Robinson(1) points out, from the time of Boethius (died 524 or 525 A.D.) to
that of Dante (1265-1321 A.D.) there was not a single writer of renown in
western Europe who was not a professional churchman. All the learning of
the time, then, centred in the priesthood. We know that the same condition
of things pertained in Egypt, when science became static there. But,
contrariwise, we have seen that in Greece and early Rome the scientific
workers were largely physicians or professional teachers; there was scarcely
a professional theologian among them.
Similarly, as we shall see in the Arabic world, where alone there was
progress in the mediaeval epoch, the learned men were, for the most part,
physicians. Now the meaning of this must be self-evident. The physician
naturally "intends" his mind towards the practicalities. His professional
studies tend to make him an investigator of the operations of nature. He is
usually a sceptic, with a spontaneous interest in practical science. But the
theologian "intends" his mind away from practicalities and towards
mysticism. He is a professional believer in the supernatural; he discounts
the value of merely "natural" phenomena. His whole attitude of mind is
unscientific; the fundamental tenets of his faith are based on alleged
occurrences which inductive science cannot admit—namely, miracles. And
so the minds "intended" towards the supernatural achieved only the hazy
mysticism of mediaeval thought. Instead of investigating natural laws, they
paid heed (as, for example, Thomas Aquinas does in his Summa Theologia)
to the "acts of angels," the "speaking of angels," the "subordination of
angels," the "deeds of guardian angels," and the like. They disputed such
important questions as, How many angels can stand upon the point of a
needle? They argued pro and con as to whether Christ were coeval with
God, or whether he had been merely created "in the beginning," perhaps
ages before the creation of the world. How could it be expected that science
should flourish when the greatest minds of the age could concern
themselves with problems such as these?
Despite our preconceptions or prejudices, there can be but one answer to
that question. Oriental superstition cast its blight upon the fair field of
science, whatever compensation it may or may not have brought in other
fields. But we must be on our guard lest we overestimate or incorrectly
estimate this influence. Posterity, in glancing backward, is always prone to
stamp any given age of the past with one idea, and to desire to characterize

it with a single phrase; whereas in reality all ages are diversified, and any
generalization regarding an epoch is sure to do that epoch something less or
something more than justice. We may be sure, then, that the ideal of
ecclesiasticism is not solely responsible for the scientific stasis of the dark
age. Indeed, there was another influence of a totally different character that
is too patent to be overlooked—the influence, namely, of the economic
condition of western Europe during this period. As I have elsewhere pointed
out,(2) Italy, the centre of western civilization, was at this time
impoverished, and hence could not provide the monetary stimulus so
essential to artistic and scientific no less than to material progress. There
were no patrons of science and literature such as the Ptolemies of that elder
Alexandrian day. There were no great libraries; no colleges to supply
opportunities and afford stimuli to the rising generation. Worst of all, it
became increasingly difficult to secure books.
This phase of the subject is often overlooked. Yet a moment's
consideration will show its importance. How should we fare to-day if no
new scientific books were being produced, and if the records of former
generations were destroyed? That is what actually happened in Europe
during the Middle Ages. At an earlier day books were made and distributed
much more abundantly than is sometimes supposed. Bookmaking had,
indeed, been an important profession in Rome, the actual makers of books
being slaves who worked under the direction of a publisher. It was through
the efforts of these workers that the classical works in Greek and Latin were
multiplied and disseminated. Unfortunately the climate of Europe does not
conduce to the indefinite preservation of a book; hence very few remnants
of classical works have come down to us in the original from a remote
period. The rare exceptions are certain papyrus fragments, found in Egypt,
some of which are Greek manuscripts dating from the third century B.C.
Even from these sources the output is meagre; and the only other repository
of classical books is a single room in the buried city of Herculaneum, which
contained several hundred manuscripts, mostly in a charred condition, a
considerable number of which, however, have been unrolled and found
more or less legible. This library in the buried city was chiefly made up of
philosophical works, some of which were quite unknown to the modern
world until discovered there.
But this find, interesting as it was from an archaeological stand-point,
had no very important bearing on our knowledge of the literature of

antiquity. Our chief dependence for our knowledge of that literature must
still be placed in such copies of books as were made in the successive
generations. Comparatively few of the extant manuscripts are older than the
tenth century of our era. It requires but a momentary consideration of the
conditions under which ancient books were produced to realize how slow
and difficult the process was before the invention of printing. The taste of
the book-buying public demanded a clearly written text, and in the Middle
Ages it became customary to produce a richly ornamented text as well. The
script employed being the prototype of the modern printed text, it will be
obvious that a scribe could produce but a few pages at best in a day. A large
work would therefore require the labor of a scribe for many months or even
for several years. We may assume, then, that it would be a very flourishing
publisher who could produce a hundred volumes all told per annum; and
probably there were not many publishers at any given time, even in the
period of Rome's greatest glory, who had anything like this output.
As there was a large number of authors in every generation of the
classical period, it follows that most of these authors must have been
obliged to content themselves with editions numbering very few copies; and
it goes without saying that the greater number of books were never
reproduced in what might be called a second edition. Even books that
retained their popularity for several generations would presently fail to
arouse sufficient interest to be copied; and in due course such works would
pass out of existence altogether. Doubtless many hundreds of books were
thus lost before the close of the classical period, the names of their authors
being quite forgotten, or preserved only through a chance reference; and of
course the work of elimination went on much more rapidly during the
Middle Ages, when the interest in classical literature sank to so low an ebb
in the West. Such collections of references and quotations as the Greek
Anthology and the famous anthologies of Stobaeus and Athanasius and
Eusebius give us glimpses of a host of writers—more than seven hundred
are quoted by Stobaeus—a very large proportion of whom are quite
unknown except through these brief excerpts from their lost works.
Quite naturally the scientific works suffered at least as largely as any
others in an age given over to ecclesiastical dreamings. Yet in some regards
there is matter for surprise as to the works preserved. Thus, as we have
seen, the very extensive works of Aristotle on natural history, and the
equally extensive natural history of Pliny, which were preserved throughout

this period, and are still extant, make up relatively bulky volumes. These
works seem to have interested the monks of the Middle Ages, while many
much more important scientific books were allowed to perish. A
considerable bulk of scientific literature was also preserved through the
curious channels of Arabic and Armenian translations. Reference has
already been made to the Almagest of Ptolemy, which, as we have seen,
was translated into Arabic, and which was at a later day brought by the
Arabs into western Europe and (at the instance of Frederick II of Sicily)
translated out of their language into mediaeval Latin.
It remains to inquire, however, through what channels the Greek works
reached the Arabs themselves. To gain an answer to this question we must
follow the stream of history from its Roman course eastward to the new seat
of the Roman empire in Byzantium. Here civilization centred from about
the fifth century A.D., and here the European came in contact with the
civilization of the Syrians, the Persians, the Armenians, and finally of the
Arabs. The Byzantines themselves, unlike the inhabitants of western
Europe, did not ignore the literature of old Greece; the Greek language
became the regular speech of the Byzantine people, and their writers made a
strenuous effort to perpetuate the idiom and style of the classical period.
Naturally they also made transcriptions of the classical authors, and thus a
great mass of literature was preserved, while the corresponding works were
quite forgotten in western Europe.
Meantime many of these works were translated into Syriac, Armenian,
and Persian, and when later on the Byzantine civilization degenerated,
many works that were no longer to be had in the Greek originals continued
to be widely circulated in Syriac, Persian, Armenian, and, ultimately, in
Arabic translations. When the Arabs started out in their conquests, which
carried them through Egypt and along the southern coast of the
Mediterranean, until they finally invaded Europe from the west by way of
Gibraltar, they carried with them their translations of many a Greek
classical author, who was introduced anew to the western world through
this strange channel.
We are told, for example, that Averrhoes, the famous commentator of
Aristotle, who lived in Spain in the twelfth century, did not know a word of
Greek and was obliged to gain his knowledge of the master through a
Syriac translation; or, as others alleged (denying that he knew even Syriac),

through an Arabic version translated from the Syriac. We know, too, that the
famous chronology of Eusebius was preserved through an Armenian
translation; and reference has more than once been made to the Arabic
translation of Ptolemy's great work, to which we still apply its Arabic title
of Almagest.
The familiar story that when the Arabs invaded Egypt they burned the
Alexandrian library is now regarded as an invention of later times. It seems
much more probable that the library bad been largely scattered before the
coming of the Moslems. Indeed, it has even been suggested that the
Christians of an earlier day removed the records of pagan thought. Be that
as it may, the famous Alexandrian library had disappeared long before the
revival of interest in classical learning. Meanwhile, as we have said, the
Arabs, far from destroying the western literature, were its chief preservers.
Partly at least because of their regard for the records of the creative work of
earlier generations of alien peoples, the Arabs were enabled to outstrip their
contemporaries. For it cannot be in doubt that, during that long stretch of
time when the western world was ignoring science altogether or at most
contenting itself with the casual reading of Aristotle and Pliny, the Arabs
had the unique distinction of attempting original investigations in science.
To them were due all important progressive steps which were made in any
scientific field whatever for about a thousand years after the time of
Ptolemy and Galen. The progress made even by the Arabs during this long
period seems meagre enough, yet it has some significant features. These
will now demand our attention.

II. MEDIAEVAL SCIENCE AMONG THE
ARABIANS
The successors of Mohammed showed themselves curiously receptive of
the ideas of the western people whom they conquered. They came in
contact with the Greeks in western Asia and in Egypt, and, as has been said,
became their virtual successors in carrying forward the torch of learning. It
must not be inferred, however, that the Arabian scholars, as a class, were
comparable to their predecessors in creative genius. On the contrary, they
retained much of the conservative oriental spirit. They were under the spell
of tradition, and, in the main, what they accepted from the Greeks they
regarded as almost final in its teaching. There were, however, a few notable
exceptions among their men of science, and to these must be ascribed
several discoveries of some importance.
The chief subjects that excited the interest and exercised the ingenuity of
the Arabian scholars were astronomy, mathematics, and medicine. The
practical phases of all these subjects were given particular attention. Thus it
is well known that our so-called Arabian numerals date from this period.
The revolutionary effect of these characters, as applied to practical
mathematics, can hardly be overestimated; but it is generally considered,
and in fact was admitted by the Arabs themselves, that these numerals were
really borrowed from the Hindoos, with whom the Arabs came in contact on
the east. Certain of the Hindoo alphabets, notably that of the Battaks of
Sumatra, give us clews to the originals of the numerals. It does not seem
certain, however, that the Hindoos employed these characters according to
the decimal system, which is the prime element of their importance.
Knowledge is not forthcoming as to just when or by whom such application
was made. If this was an Arabic innovation, it was perhaps the most
important one with which that nation is to be credited. Another
mathematical improvement was the introduction into trigonometry of the
sine—the half-chord of the double arc—instead of the chord of the arc itself
which the Greek astronomers had employed. This improvement was due to
the famous Albategnius, whose work in other fields we shall examine in a
moment.

Another evidence of practicality was shown in the Arabian method of
attempting to advance upon Eratosthenes' measurement of the earth. Instead
of trusting to the measurement of angles, the Arabs decided to measure
directly a degree of the earth's surface—or rather two degrees. Selecting a
level plain in Mesopotamia for the experiment, one party of the surveyors
progressed northward, another party southward, from a given point to the
distance of one degree of arc, as determined by astronomical observations.
The result found was fifty-six miles for the northern degree, and fifty-six
and two-third miles for the southern. Unfortunately, we do not know the
precise length of the mile in question, and therefore cannot be assured as to
the accuracy of the measurement. It is interesting to note, however, that the
two degrees were found of unequal lengths, suggesting that the earth is not
a perfect sphere—a suggestion the validity of which was not to be put to the
test of conclusive measurements until about the close of the eighteenth
century. The Arab measurement was made in the time of Caliph Abdallah
al-Mamun, the son of the famous Harun-al-Rashid. Both father and son
were famous for their interest in science. Harun-al-Rashid was, it will be
recalled, the friend of Charlemagne. It is said that he sent that ruler, as a
token of friendship, a marvellous clock which let fall a metal ball to mark
the hours. This mechanism, which is alleged to have excited great wonder
in the West, furnishes yet another instance of Arabian practicality.
Perhaps the greatest of the Arabian astronomers was Mohammed ben
Jabir Albategnius, or El-batani, who was born at Batan, in Mesopotamia,
about the year 850 A.D., and died in 929. Albategnius was a student of the
Ptolemaic astronomy, but he was also a practical observer. He made the
important discovery of the motion of the solar apogee. That is to say, he
found that the position of the sun among the stars, at the time of its greatest
distance from the earth, was not what it had been in the time of Ptolemy.
The Greek astronomer placed the sun in longitude 65 degrees, but
Albategnius found it in longitude 82 degrees, a distance too great to be
accounted for by inaccuracy of measurement. The modern inference from
this observation is that the solar system is moving through space; but of
course this inference could not well be drawn while the earth was regarded
as the fixed centre of the universe.
In the eleventh century another Arabian discoverer, Arzachel, observing
the sun to be less advanced than Albategnius had found it, inferred
incorrectly that the sun had receded in the mean time. The modern

explanation of this observation is that the measurement of Albategnius was
somewhat in error, since we know that the sun's motion is steadily
progressive. Arzachel, however, accepting the measurement of his
predecessor, drew the false inference of an oscillatory motion of the stars,
the idea of the motion of the solar system not being permissible. This
assumed phenomenon, which really has no existence in point of fact, was
named the "trepidation of the fixed stars," and was for centuries accepted as
an actual phenomenon. Arzachel explained this supposed phenomenon by
assuming that the equinoctial points, or the points of intersection of the
equator and the ecliptic, revolve in circles of eight degrees' radius. The first
points of Aries and Libra were supposed to describe the circumference of
these circles in about eight hundred years. All of which illustrates how a
difficult and false explanation may take the place of a simple and correct
one. The observations of later generations have shown conclusively that the
sun's shift of position is regularly progressive, hence that there is no
"trepidation" of the stars and no revolution of the equinoctial points.
If the Arabs were wrong as regards this supposed motion of the fixed
stars, they made at least one correct observation as to the inequality of
motion of the moon. Two inequalities of the motion of this body were
already known. A third, called the moon's variation, was discovered by an
Arabian astronomer who lived at Cairo and observed at Bagdad in 975, and
who bore the formidable name of Mohammed Aboul Wefaal-Bouzdjani.
The inequality of motion in question, in virtue of which the moon moves
quickest when she is at new or full, and slowest at the first and third quarter,
was rediscovered by Tycho Brahe six centuries later; a fact which in itself
evidences the neglect of the Arabian astronomer's discovery by his
immediate successors.
In the ninth and tenth centuries the Arabian city of Cordova, in Spain,
was another important centre of scientific influence. There was a library of
several hundred thousand volumes here, and a college where mathematics
and astronomy were taught. Granada, Toledo, and Salamanca were also
important centres, to which students flocked from western Europe. It was
the proximity of these Arabian centres that stimulated the scientific interests
of Alfonso X. of Castile, at whose instance the celebrated Alfonsine tables
were constructed. A familiar story records that Alfonso, pondering the
complications of the Ptolemaic cycles and epicycles, was led to remark that,
had he been consulted at the time of creation, he could have suggested a

much better and simpler plan for the universe. Some centuries were to
elapse before Copernicus was to show that it was not the plan of the
universe, but man's interpretation of it, that was at fault.
Another royal personage who came under Arabian influence was
Frederick II. of Sicily—the "Wonder of the World," as he was called by his
contemporaries. The Almagest of Ptolemy was translated into Latin at his
instance, being introduced to the Western world through this curious
channel. At this time it became quite usual for the Italian and Spanish
scholars to understand Arabic although they were totally ignorant of Greek.
In the field of physical science one of the most important of the Arabian
scientists was Alhazen. His work, published about the year 1100 A.D., had
great celebrity throughout the mediaeval period. The original investigations
of Alhazen had to do largely with optics. He made particular studies of the
eye itself, and the names given by him to various parts of the eye, as the
vitreous humor, the cornea, and the retina, are still retained by anatomists. It
is known that Ptolemy had studied the refraction of light, and that he, in
common with his immediate predecessors, was aware that atmospheric
refraction affects the apparent position of stars near the horizon. Alhazen
carried forward these studies, and was led through them to make the first
recorded scientific estimate of the phenomena of twilight and of the height
of the atmosphere. The persistence of a glow in the atmosphere after the sun
has disappeared beneath the horizon is so familiar a phenomenon that the
ancient philosophers seem not to have thought of it as requiring an
explanation. Yet a moment's consideration makes it clear that, if light
travels in straight lines and the rays of the sun were in no wise deflected,
the complete darkness of night should instantly succeed to day when the
sun passes below the horizon. That this sudden change does not occur,
Alhazen explained as due to the reflection of light by the earth's
atmosphere.
Alhazen appears to have conceived the atmosphere as a sharply defined
layer, and, assuming that twilight continues only so long as rays of the sun
reflected from the outer surface of this layer can reach the spectator at any
given point, he hit upon a means of measurement that seemed to solve the
hitherto inscrutable problem as to the atmospheric depth. Like the
measurements of Aristarchus and Eratosthenes, this calculation of Alhazen
is simple enough in theory. Its defect consists largely in the difficulty of

fixing its terms with precision, combined with the further fact that the rays
of the sun, in taking the slanting course through the earth's atmosphere, are
really deflected from a straight line in virtue of the constantly increasing
density of the air near the earth's surface. Alhazen must have been aware of
this latter fact, since it was known to the later Alexandrian astronomers, but
he takes no account of it in the present measurement. The diagram will
make the method of Alhazen clear.
His important premises are two: first, the well-recognized fact that, when
light is reflected from any surface, the angle of incidence is equal to the
angle of reflection; and, second, the much more doubtful observation that
twilight continues until such time as the sun, according to a simple
calculation, is nineteen degrees below the horizon. Referring to the
diagram, let the inner circle represent the earth's surface, the outer circle the
limits of the atmosphere, C being the earth's centre, and RR radii of the
earth. Then the observer at the point A will continue to receive the reflected
rays of the sun until that body reaches the point S, which is, according to
the hypothesis, nineteen degrees below the horizon line of the observer at
A. This horizon line, being represented by AH, and the sun's ray by SM, the
angle HMS is an angle of nineteen degrees. The complementary angle SMA
is, obviously, an angle of (180-19) one hundred and sixty-one degrees. But
since M is the reflecting surface and the angle of incidence equals the angle
of reflection, the angle AMC is an angle of one-half of one hundred and
sixty-one degrees, or eighty degrees and thirty minutes. Now this angle
AMC, being known, the right-angled triangle MAC is easily resolved, since
the side AC of that triangle, being the radius of the earth, is a known
dimension. Resolution of this triangle gives us the length of the hypotenuse
MC, and the difference between this and the radius (AC), or CD, is
obviously the height of the atmosphere (h), which was the measurement
desired. According to the calculation of Alhazen, this h, or the height of the
atmosphere, represents from twenty to thirty miles. The modern
computation extends this to about fifty miles. But, considering the various
ambiguities that necessarily attended the experiment, the result was a
remarkably close approximation to the truth.
Turning from physics to chemistry, we find as perhaps the greatest
Arabian name that of Geber, who taught in the College of Seville in the first
half of the eighth century. The most important researches of this really
remarkable experimenter had to do with the acids. The ancient world had

had no knowledge of any acid more powerful than acetic. Geber, however,
vastly increased the possibilities of chemical experiment by the discovery
of sulphuric, nitric, and nitromuriatic acids. He made use also of the
processes of sublimation and filtration, and his works describe the water
bath and the chemical oven. Among the important chemicals which he first
differentiated is oxide of mercury, and his studies of sulphur in its various
compounds have peculiar interest. In particular is this true of his
observation that, tinder certain conditions of oxidation, the weight of a
metal was lessened.
From the record of these studies in the fields of astronomy, physics, and
chemistry, we turn to a somewhat extended survey of the Arabian advances
in the field of medicine.
ARABIAN MEDICINE
The influence of Arabian physicians rested chiefly upon their use of
drugs rather than upon anatomical knowledge. Like the mediaeval
Christians, they looked with horror on dissection of the human body; yet
there were always among them investigators who turned constantly to
nature herself for hidden truths, and were ready to uphold the superiority of
actual observation to mere reading. Thus the physician Abd el-Letif, while
in Egypt, made careful studies of a mound of bones containing more than
twenty thousand skeletons. While examining these bones he discovered that
the lower jaw consists of a single bone, not of two, as had been taught by
Galen. He also discovered several other important mistakes in Galenic
anatomy, and was so impressed with his discoveries that he contemplated
writing a work on anatomy which should correct the great classical
authority's mistakes.
It was the Arabs who invented the apothecary, and their pharmacopoeia,
issued from the hospital at Gondisapor, and elaborated from time to time,
formed the basis for Western pharmacopoeias. Just how many drugs
originated with them, and how many were borrowed from the Hindoos,
Jews, Syrians, and Persians, cannot be determined. It is certain, however,
that through them various new and useful drugs, such as senna, aconite,
rhubarb, camphor, and mercury, were handed down through the Middle
Ages, and that they are responsible for the introduction of alcohol in the
field of therapeutics.

In mediaeval Europe, Arabian science came to be regarded with
superstitious awe, and the works of certain Arabian physicians were exalted
to a position above all the ancient writers. In modern times, however, there
has been a reaction and a tendency to depreciation of their work. By some
they are held to be mere copyists or translators of Greek books, and in no
sense original investigators in medicine. Yet there can be little doubt that
while the Arabians did copy and translate freely, they also originated and
added considerably to medical knowledge. It is certain that in the time when
Christian monarchs in western Europe were paying little attention to
science or education, the caliphs and vizirs were encouraging physicians
and philosophers, building schools, and erecting libraries and hospitals.
They made at least a creditable effort to uphold and advance upon the
scientific standards of an earlier age.
The first distinguished Arabian physician was Harets ben Kaladah, who
received his education in the Nestonian school at Gondisapor, about the
beginning of the seventh century. Notwithstanding the fact that Harets was
a Christian, he was chosen by Mohammed as his chief medical adviser, and
recommended as such to his successor, the Caliph Abu Bekr. Thus, at the
very outset, the science of medicine was divorced from religion among the
Arabians; for if the prophet himself could employ the services of an
unbeliever, surely others might follow his example. And that this example
was followed is shown in the fact that many Christian physicians were
raised to honorable positions by succeeding generations of Arabian
monarchs. This broad-minded view of medicine taken by the Arabs
undoubtedly assisted as much as any one single factor in upbuilding the
science, just as the narrow and superstitious view taken by Western nations
helped to destroy it.
The education of the Arabians made it natural for them to associate
medicine with the natural sciences, rather than with religion. An Arabian
savant was supposed to be equally well educated in philosophy,
jurisprudence, theology, mathematics, and medicine, and to practise law,
theology, and medicine with equal skill upon occasion. It is easy to
understand, therefore, why these religious fanatics were willing to employ
unbelieving physicians, and their physicians themselves to turn to the
scientific works of Hippocrates and Galen for medical instruction, rather
than to religious works. Even Mohammed himself professed some
knowledge of medicine, and often relied upon this knowledge in treating

ailments rather than upon prayers or incantations. He is said, for example,
to have recommended and applied the cautery in the case of a friend who,
when suffering from angina, had sought his aid.
The list of eminent Arabian physicians is too long to be given here, but
some of them are of such importance in their influence upon later medicine
that they cannot be entirely ignored. One of the first of these was Honain
ben Isaac (809-873 A.D.), a Christian Arab of Bagdad. He made translations
of the works of Hippocrates, and practised the art along the lines indicated
by his teachings and those of Galen. He is considered the greatest translator
of the ninth century and one of the greatest philosophers of that period.
Another great Arabian physician, whose work was just beginning as
Honain's was drawing to a close, was Rhazes (850-923 A.D.), who during
his life was no less noted as a philosopher and musician than as a physician.
He continued the work of Honain, and advanced therapeutics by
introducing more extensive use of chemical remedies, such as mercurial
ointments, sulphuric acid, and aqua vitae. He is also credited with being the
first physician to describe small-pox and measles accurately.
While Rhazes was still alive another Arabian, Haly Abbas (died about
994), was writing his famous encyclopaedia of medicine, called The Royal
Book. But the names of all these great physicians have been considerably
obscured by the reputation of Avicenna (980-1037), the Arabian "Prince of
Physicians," the greatest name in Arabic medicine, and one of the most
remarkable men in history. Leclerc says that "he was perhaps never
surpassed by any man in brilliancy of intellect and indefatigable activity."
His career was a most varied one. He was at all times a boisterous reveller,
but whether flaunting gayly among the guests of an emir or biding in some
obscure apothecary cellar, his work of philosophical writing was carried on
steadily. When a friendly emir was in power, he taught and wrote and
caroused at court; but between times, when some unfriendly ruler was
supreme, he was hiding away obscurely, still pouring out his great mass of
manuscripts. In this way his entire life was spent.
By his extensive writings he revived and kept alive the best of the
teachings of the Greek physicians, adding to them such observations as he
had made in anatomy, physiology, and materia medica. Among his
discoveries is that of the contagiousness of pulmonary tuberculosis. His
works for several centuries continued to be looked upon as the highest

standard by physicians, and he should undoubtedly be credited with having
at least retarded the decline of mediaeval medicine.
But it was not the Eastern Arabs alone who were active in the field of
medicine. Cordova, the capital of the western caliphate, became also a great
centre of learning and produced several great physicians. One of these,
Albucasis (died in 1013 A.D.), is credited with having published the first
illustrated work on surgery, this book being remarkable in still another way,
in that it was also the first book, since classical times, written from the
practical experience of the physician, and not a mere compilation of ancient
authors. A century after Albucasis came the great physician Avenzoar
(1113-1196), with whom he divides about equally the medical honors of the
western caliphate. Among Avenzoar's discoveries was that of the cause of
"itch"—a little parasite, "so small that he is hardly visible." The discovery
of the cause of this common disease seems of minor importance now, but it
is of interest in medical history because, had Avenzoar's discovery been
remembered a hundred years ago, "itch struck in" could hardly have been
considered the cause of three-fourths of all diseases, as it was by the famous
Hahnemann.
The illustrious pupil of Avenzoar, Averrhoes, who died in 1198 A.D., was
the last of the great Arabian physicians who, by rational conception of
medicine, attempted to stem the flood of superstition that was
overwhelming medicine. For a time he succeeded; but at last the Moslem
theologians prevailed, and he was degraded and banished to a town
inhabited only by the despised Jews.
ARABIAN HOSPITALS
To early Christians belong the credit of having established the first
charitable institutions for caring for the sick; but their efforts were soon
eclipsed by both Eastern and Western Mohammedans. As early as the eighth
century the Arabs had begun building hospitals, but the flourishing time of
hospital building seems to have begun early in the tenth century. Lady
Seidel, in 918 A.D., opened a hospital at Bagdad, endowed with an amount
corresponding to about three hundred pounds sterling a month. Other
similar hospitals were erected in the years immediately following, and in
977 the Emir Adad-adaula established an enormous institution with a staff
of twenty-four medical officers. The great physician Rhazes is said to have
selected the site for one of these hospitals by hanging pieces of meat in

various places about the city, selecting the site near the place at which
putrefaction was slowest in making its appearance. By the middle of the
twelfth century there were something like sixty medical institutions in
Bagdad alone, and these institutions were free to all patients and supported
by official charity.
The Emir Nureddin, about the year 1160, founded a great hospital at
Damascus, as a thank-offering for his victories over the Crusaders. This
great institution completely overshadowed all the earlier Moslem hospitals
in size and in the completeness of its equipment. It was furnished with
facilities for teaching, and was conducted for several centuries in a lavish
manner, regardless of expense. But little over a century after its foundation
the fame of its methods of treatment led to the establishment of a larger and
still more luxurious institution—the Mansuri hospital at Cairo. It seems that
a certain sultan, having been cured by medicines from the Damascene
hospital, determined to build one of his own at Cairo which should eclipse
even the great Damascene institution.
In a single year (1283-1284) this hospital was begun and completed. No
efforts were spared in hurrying on the good work, and no one was exempt
from performing labor on the building if he chanced to pass one of the
adjoining streets. It was the order of the sultan that any person passing near
could be impressed into the work, and this order was carried out to the
letter, noblemen and beggars alike being forced to lend a hand. Very
naturally, the adjacent thoroughfares became unpopular and practically
deserted, but still the holy work progressed rapidly and was shortly
completed.
This immense structure is said to have contained four courts, each having
a fountain in the centre; lecture-halls, wards for isolating certain diseases,
and a department that corresponded to the modern hospital's "out-patient"
department. The yearly endowment amounted to something like the
equivalent of one hundred and twenty-five thousand dollars. A novel feature
was a hall where musicians played day and night, and another where story-
tellers were employed, so that persons troubled with insomnia were amused
and melancholiacs cheered. Those of a religious turn of mind could listen to
readings of the Koran, conducted continuously by a staff of some fifty
chaplains. Each patient on leaving the hospital received some gold pieces,
that he need not be obliged to attempt hard labor at once.

In considering the astonishing tales of these sumptuous Arabian
institutions, it should be borne in mind that our accounts of them are, for the
most part, from Mohammedan sources. Nevertheless, there can be little
question that they were enormous institutions, far surpassing any similar
institutions in western Europe. The so-called hospitals in the West were, at
this time, branches of monasteries under supervision of the monks, and did
not compare favorably with the Arabian hospitals.
But while the medical science of the Mohammedans greatly
overshadowed that of the Christians during this period, it did not
completely obliterate it. About the year 1000 A.D. came into prominence
the Christian medical school at Salerno, situated on the Italian coast, some
thirty miles southeast of Naples. Just how long this school had been in
existence, or by whom it was founded, cannot be determined, but its period
of greatest influence was the eleventh, twelfth, and thirteenth centuries. The
members of this school gradually adopted Arabic medicine, making use of
many drugs from the Arabic pharmacopoeia, and this formed one of the
stepping-stones to the introduction of Arabian medicine all through western
Europe.
It was not the adoption of Arabian medicines, however, that has made the
school at Salerno famous both in rhyme and prose, but rather the fact that
women there practised the healing art. Greatest among them was Trotula,
who lived in the eleventh century, and whose learning is reputed to have
equalled that of the greatest physicians of the day. She is accredited with a
work on Diseases of Women, still extant, and many of her writings on
general medical subjects were quoted through two succeeding centuries. If
we may judge from these writings, she seemed to have had many excellent
ideas as to the proper methods of treating diseases, but it is difficult to
determine just which of the writings credited to her are in reality hers.
Indeed, the uncertainty is even greater than this implies, for, according to
some writers, "Trotula" is merely the title of a book. Such an authority as
Malgaigne, however, believed that such a woman existed, and that the
works accredited to her are authentic. The truth of the matter may perhaps
never be fully established, but this at least is certain—the tradition in regard
to Trotula could never have arisen had not women held a far different
position among the Arabians of this period from that accorded them in
contemporary Christendom.

III. MEDIAEVAL SCIENCE IN THE WEST
We have previously referred to the influence of the Byzantine civilization
in transmitting the learning of antiquity across the abysm of the dark age. It
must be admitted, however, that the importance of that civilization did not
extend much beyond the task of the common carrier. There were no great
creative scientists in the later Roman empire of the East any more than in
the corresponding empire of the West. There was, however, one field in
which the Byzantine made respectable progress and regarding which their
efforts require a few words of special comment. This was the field of
medicine.
The Byzantines of this time could boast of two great medical men, Aetius
of Amida (about 502-575 A.D.) and Paul of Aegina (about 620-690). The
works of Aetius were of value largely because they recorded the teachings
of many of his eminent predecessors, but he was not entirely lacking in
originality, and was perhaps the first physician to mention diphtheria, with
an allusion to some observations of the paralysis of the palate which
sometimes follows this disease.
Paul of Aegina, who came from the Alexandrian school about a century
later, was one of those remarkable men whose ideas are centuries ahead of
their time. This was particularly true of Paul in regard to surgery, and his
attitude towards the supernatural in the causation and treatment of diseases.
He was essentially a surgeon, being particularly familiar with military
surgery, and some of his descriptions of complicated and difficult
operations have been little improved upon even in modern times. In his
books he describes such operations as the removal of foreign bodies from
the nose, ear, and esophagus; and he recognizes foreign growths such as
polypi in the air-passages, and gives the method of their removal. Such
operations as tracheotomy, tonsillotomy, bronchotomy, staphylotomy, etc.,
were performed by him, and he even advocated and described puncture of
the abdominal cavity, giving careful directions as to the location in which
such punctures should be made. He advocated amputation of the breast for
the cure of cancer, and described extirpation of the uterus. Just how
successful this last operation may have been as performed by him does not

appear; but he would hardly have recommended it if it had not been
sometimes, at least, successful. That he mentions it at all, however, is
significant, as this difficult operation is considered one of the great triumphs
of modern surgery.
But Paul of Aegina is a striking exception to the rule among Byzantine
surgeons, and as he was their greatest, so he was also their last important
surgeon. The energies of all Byzantium were so expended in religious
controversies that medicine, like the other sciences, was soon relegated to a
place among the other superstitions, and the influence of the Byzantine
school was presently replaced by that of the conquering Arabians.
THIRTEENTH-CENTURY MEDICINE
The thirteenth century marks the beginning of a gradual change in
medicine, and a tendency to leave the time-worn rut of superstitious
dogmas that so long retarded the progress of science. It is thought that the
great epidemics which raged during the Middle Ages acted powerfully in
diverting the medical thought of the times into new and entirely different
channels. It will be remembered that the teachings of Galen were handed
through mediaeval times as the highest and best authority on the subject of
all diseases. When, however, the great epidemics made their appearance,
the medical men appealed to the works of Galen in vain for enlightenment,
as these works, having been written several centuries before the time of the
plagues, naturally contained no information concerning them. It was
evident, therefore, that on this subject, at least, Galen was not infallible; and
it would naturally follow that, one fallible point having been revealed,
others would be sought for. In other words, scepticism in regard to accepted
methods would be aroused, and would lead naturally, as such scepticism
usually does, to progress. The devastating effects of these plagues, despite
prayers and incantations, would arouse doubt in the minds of many as to the
efficacy of superstitious rites and ceremonies in curing diseases. They had
seen thousands and tens of thousands of their fellow-beings swept away by
these awful scourges. They had seen the ravages of these epidemics
continue for months or even years, notwithstanding the fact that multitudes
of God-fearing people prayed hourly that such ravages might be checked.
And they must have observed also that when even very simple rules of
cleanliness and hygiene were followed there was a diminution in the
ravages of the plague, even without the aid of incantations. Such

observations as these would have a tendency to awaken a suspicion in the
minds of many of the physicians that disease was not a manifestation of the
supernatural, but a natural phenomenon, to be treated by natural methods.
But, be the causes what they may, it is a fact that the thirteenth century
marks a turning-point, or the beginning of an attitude of mind which
resulted in bringing medicine to a much more rational position. Among the
thirteenth-century physicians, two men are deserving of special mention.
These are Arnald of Villanova (1235-1312) and Peter of Abano (1250-
1315). Both these men suffered persecution for expressing their belief in
natural, as against the supernatural, causes of disease, and at one time
Arnald was obliged to flee from Barcelona for declaring that the "bulls" of
popes were human works, and that "acts of charity were dearer to God than
hecatombs." He was also accused of alchemy. Fleeing from persecution, he
finally perished by shipwreck.
Arnald was the first great representative of the school of Montpellier. He
devoted much time to the study of chemicals, and was active in attempting
to re-establish the teachings of Hippocrates and Galen. He was one of the
first of a long line of alchemists who, for several succeeding centuries,
expended so much time and energy in attempting to find the "elixir of life."
The Arab discovery of alcohol first deluded him into the belief that the
"elixir" had at last been found; but later he discarded it and made extensive
experiments with brandy, employing it in the treatment of certain diseases
—the first record of the administration of this liquor as a medicine. Arnald
also revived the search for some anaesthetic that would produce
insensibility to pain in surgical operations. This idea was not original with
him, for since very early times physicians had attempted to discover such an
anaesthetic, and even so early a writer as Herodotus tells how the Scythians,
by inhalation of the vapors of some kind of hemp, produced complete
insensibility. It may have been these writings that stimulated Arnald to
search for such an anaesthetic. In a book usually credited to him, medicines
are named and methods of administration described which will make the
patient insensible to pain, so that "he may be cut and feel nothing, as though
he were dead." For this purpose a mixture of opium, mandragora, and
henbane is to be used. This mixture was held at the patient's nostrils much
as ether and chloroform are administered by the modern surgeon. The
method was modified by Hugo of Lucca (died in 1252 or 1268), who added
certain other narcotics, such as hemlock, to the mixture, and boiled a new

sponge in this decoction. After boiling for a certain time, this sponge was
dried, and when wanted for use was dipped in hot water and applied to the
nostrils.
Just how frequently patients recovered from the administration of such a
combination of powerful poisons does not appear, but the percentage of
deaths must have been very high, as the practice was generally condemned.
Insensibility could have been produced only by swallowing large quantities
of the liquid, which dripped into the nose and mouth when the sponge was
applied, and a lethal quantity might thus be swallowed. The method was
revived, with various modifications, from time to time, but as often fell into
disuse. As late as 1782 it was sometimes attempted, and in that year the
King of Poland is said to have been completely anaesthetized and to have
recovered, after a painless amputation had been performed by the surgeons.
Peter of Abano was one of the first great men produced by the University
of Padua. His fate would have been even more tragic than that of the
shipwrecked Arnald had he not cheated the purifying fagots of the church
by dying opportunely on the eve of his execution for heresy. But if his spirit
had cheated the fanatics, his body could not, and his bones were burned for
his heresy. He had dared to deny the existence of a devil, and had suggested
that the case of a patient who lay in a trance for three days might help to
explain some miracles, like the raising of Lazarus.
His great work was Conciliator Differentiarum, an attempt to reconcile
physicians and philosophers. But his researches were not confined to
medicine, for he seems to have had an inkling of the hitherto unknown fact
that air possesses weight, and his calculation of the length of the year at
three hundred and sixty-five days, six hours, and four minutes, is
exceptionally accurate for the age in which he lived. He was probably the
first of the Western writers to teach that the brain is the source of the nerves,
and the heart the source of the vessels. From this it is seen that he was
groping in the direction of an explanation of the circulation of the blood, as
demonstrated by Harvey three centuries later.
The work of Arnald and Peter of Abano in "reviving" medicine was
continued actively by Mondino (1276-1326) of Bologna, the "restorer of
anatomy," and by Guy of Chauliac: (born about 1300), the "restorer of
surgery." All through the early Middle Ages dissections of human bodies
had been forbidden, and even dissection of the lower animals gradually fell

into disrepute because physicians detected in such practices were
sometimes accused of sorcery. Before the close of the thirteenth century,
however, a reaction had begun, physicians were protected, and dissections
were occasionally sanctioned by the ruling monarch. Thus Emperor
Frederick H. (1194-1250 A.D.)—whose services to science we have already
had occasion to mention—ordered that at least one human body should be
dissected by physicians in his kingdom every five years. By the time of
Mondino dissections were becoming more frequent, and he himself is
known to have dissected and demonstrated several bodies. His writings on
anatomy have been called merely plagiarisms of Galen, but in all
probability be made many discoveries independently, and on the whole, his
work may be taken as more advanced than Galen's. His description of the
heart is particularly accurate, and he seems to have come nearer to
determining the course of the blood in its circulation than any of his
predecessors. In this quest he was greatly handicapped by the prevailing
belief in the idea that blood-vessels must contain air as well as blood, and
this led him to assume that one of the cavities of the heart contained
"spirits," or air. It is probable, however, that his accurate observations, so
far as they went, were helpful stepping-stones to Harvey in his discovery of
the circulation.
Guy of Chauliac, whose innovations in surgery reestablished that science
on a firm basis, was not only one of the most cultured, but also the most
practical surgeon of his time. He had great reverence for the works of
Galen, Albucasis, and others of his noted predecessors; but this reverence
did not blind him to their mistakes nor prevent him from using rational
methods of treatment far in advance of theirs. His practicality is shown in
some of his simple but useful inventions for the sick-room, such as the
device of a rope, suspended from the ceiling over the bed, by which a
patient may move himself about more easily; and in some of his
improvements in surgical dressings, such as stiffening bandages by dipping
them in the white of an egg so that they are held firmly. He treated broken
limbs in the suspended cradle still in use, and introduced the method of
making "traction" on a broken limb by means of a weight and pulley, to
prevent deformity through shortening of the member. He was one of the
first physicians to recognize the utility of spectacles, and recommended
them in cases not amenable to treatment with lotions and eye-waters. In
some of his surgical operations, such as trephining for fracture of the skull,

his technique has been little improved upon even in modern times. In one of
these operations he successfully removed a portion of a man's brain.
Surgery was undoubtedly stimulated greatly at this period by the constant
wars. Lay physicians, as a class, had been looked down upon during the
Dark Ages; but with the beginning of the return to rationalism, the services
of surgeons on the battle-field, to remove missiles from wounds, and to care
for wounds and apply dressings, came to be more fully appreciated. In
return for his labors the surgeon was thus afforded better opportunities for
observing wounds and diseases, which led naturally to a gradual
improvement in surgical methods.
FIFTEENTH-CENTURY MEDICINE
The thirteenth and fourteenth centuries had seen some slight
advancement in the science of medicine; at least, certain surgeons and
physicians, if not the generality, had made advances; but it was not until the
fifteenth century that the general revival of medical learning became
assured. In this movement, naturally, the printing-press played an all-
important part. Medical books, hitherto practically inaccessible to the great
mass of physicians, now became common, and this output of reprints of
Greek and Arabic treatises revealed the fact that many of the supposed true
copies were spurious. These discoveries very naturally aroused all manner
of doubt and criticism, which in turn helped in the development of
independent thought.
A certain manuscript of the great Cornelius Celsus, the De Medicine,
which had been lost for many centuries, was found in the church of St.
Ambrose, at Milan, in 1443, and was at once put into print. The effect of the
publication of this book, which had lain in hiding for so many centuries,
was a revelation, showing the medical profession how far most of their
supposed true copies of Celsus had drifted away from the original. The
indisputable authenticity of this manuscript, discovered and vouched for by
the man who shortly after became Pope Nicholas V., made its publication
the more impressive. The output in book form of other authorities followed
rapidly, and the manifest discrepancies between such teachers as Celsus,
Hippocrates, Galen, and Pliny heightened still more the growing spirit of
criticism.
These doubts resulted in great controversies as to the proper treatment of
certain diseases, some physicians following Hippocrates, others Galen or

Celsus, still others the Arabian masters. One of the most bitter of these
contests was over the question of "revulsion," and "derivation"—that is,
whether in cases of pleurisy treated by bleeding, the venesection should be
made at a point distant from the seat of the disease, as held by the
"revulsionists," or at a point nearer and on the same side of the body, as
practised by the "derivationists." That any great point for discussion could
be raised in the fifteenth or sixteenth centuries on so simple a matter as it
seems to-day shows how necessary to the progress of medicine was the
discovery of the circulation of the blood made by Harvey two centuries
later. After Harvey's discovery no such discussion could have been possible,
because this discovery made it evident that as far as the general effect upon
the circulation is concerned, it made little difference whether the bleeding
was done near a diseased part or remote from it. But in the sixteenth century
this question was the all-absorbing one among the doctors. At one time the
faculty of Paris condemned "derivation"; but the supporters of this method
carried the war still higher, and Emperor Charles V. himself was appealed
to. He reversed the decision of the Paris faculty, and decided in favor of
"derivation." His decision was further supported by Pope Clement VII.,
although the discussion dragged on until cut short by Harvey's discovery.
But a new form of injury now claimed the attention of the surgeons,
something that could be decided by neither Greek nor Arabian authors, as
the treatment of gun-shot wounds was, for obvious reasons, not given in
their writings. About this time, also, came the great epidemics, "the
sweating sickness" and scurvy; and upon these subjects, also, the Greeks
and Arabians were silent. John of Vigo, in his book, the Practica Copiosa,
published in 1514, and repeated in many editions, became the standard
authority on all these subjects, and thus supplanted the works of the ancient
writers.
According to Vigo, gun-shot wounds differed from the wounds made by
ordinary weapons—that is, spear, arrow, sword, or axe—in that the bullet,
being round, bruised rather than cut its way through the tissues; it burned
the flesh; and, worst of all, it poisoned it. Vigo laid especial stress upon
treating this last condition, recommending the use of the cautery or the oil
of elder, boiling hot. It is little wonder that gun-shot wounds were so likely
to prove fatal. Yet, after all, here was the germ of the idea of antisepsis.
NEW BEGINNINGS IN GENERAL SCIENCE

We have dwelt thus at length on the subject of medical science, because it
was chiefly in this field that progress was made in the Western world during
the mediaeval period, and because these studies furnished the point of
departure for the revival all along the line. It will be understood, however,
from what was stated in the preceding chapter, that the Arabian influences
in particular were to some extent making themselves felt along other lines.
The opportunity afforded a portion of the Western world—notably Spain
and Sicily—to gain access to the scientific ideas of antiquity through Arabic
translations could not fail of influence. Of like character, and perhaps even
more pronounced in degree, was the influence wrought by the Byzantine
refugees, who, when Constantinople began to be threatened by the Turks,
migrated to the West in considerable numbers, bringing with them a
knowledge of Greek literature and a large number of precious works which
for centuries had been quite forgotten or absolutely ignored in Italy. Now
Western scholars began to take an interest in the Greek language, which had
been utterly neglected since the beginning of the Middle Ages. Interesting
stories are told of the efforts made by such men as Cosmo de' Medici to
gain possession of classical manuscripts. The revival of learning thus
brought about had its first permanent influence in the fields of literature and
art, but its effect on science could not be long delayed. Quite independently
of the Byzantine influence, however, the striving for better intellectual
things had manifested itself in many ways before the close of the thirteenth
century. An illustration of this is found in the almost simultaneous
development of centres of teaching, which developed into the universities
of Italy, France, England, and, a little later, of Germany.
The regular list of studies that came to be adopted everywhere comprised
seven nominal branches, divided into two groups—the so-called
quadrivium, comprising music, arithmetic, geometry, and astronomy; and
the trivium comprising grammar, rhetoric, and logic. The vagueness of
implication of some of these branches gave opportunity to the teacher for
the promulgation of almost any knowledge of which he might be possessed,
but there can be no doubt that, in general, science had but meagre share in
the curriculum. In so far as it was given representation, its chief field must
have been Ptolemaic astronomy. The utter lack of scientific thought and
scientific method is illustrated most vividly in the works of the greatest men
of that period—such men as Albertus Magnus, Thomas Aquinas,
Bonaventura, and the hosts of other scholastics of lesser rank. Yet the

mental awakening implied in their efforts was sure to extend to other fields,
and in point of fact there was at least one contemporary of these great
scholastics whose mind was intended towards scientific subjects, and who
produced writings strangely at variance in tone and in content with the
others. This anachronistic thinker was the English monk, Roger Bacon.
ROGER BACON
Bacon was born in 1214 and died in 1292. By some it is held that he was
not appreciated in his own time because he was really a modern scientist
living in an age two centuries before modern science or methods of modern
scientific thinking were known. Such an estimate, however, is a manifest
exaggeration of the facts, although there is probably a grain of truth in it
withal. His learning certainly brought him into contact with the great
thinkers of the time, and his writings caused him to be imprisoned by his
fellow-churchmen at different times, from which circumstances we may
gather that he was advanced thinker, even if not a modern scientist.
Although Bacon was at various times in durance, or under surveillance,
and forbidden to write, he was nevertheless a marvellously prolific writer,
as is shown by the numerous books and unpublished manuscripts of his still
extant. His master-production was the Opus Majus. In Part IV. of this work
he attempts to show that all sciences rest ultimately on mathematics; but
Part V., which treats of perspective, is of particular interest to modern
scientists, because in this he discusses reflection and refraction, and the
properties of mirrors and lenses. In this part, also, it is evident that he is
making use of such Arabian writers as Alkindi and Alhazen, and this is of
especial interest, since it has been used by his detractors, who accuse him of
lack of originality, to prove that his seeming inventions and discoveries
were in reality adaptations of the Arab scientists. It is difficult to determine
just how fully such criticisms are justified. It is certain, however, that in this
part he describes the anatomy of the eye with great accuracy, and discusses
mirrors and lenses.
The magnifying power of the segment of a glass sphere had been noted
by Alhazen, who had observed also that the magnification was increased by
increasing the size of the segment used. Bacon took up the discussion of the
comparative advantages of segments, and in this discussion seems to show
that he understood how to trace the progress of the rays of light through a
spherical transparent body, and how to determine the place of the image. He

also described a method of constructing a telescope, but it is by no means
clear that he had ever actually constructed such an instrument. It is also a
mooted question as to whether his instructions as to the construction of such
an instrument would have enabled any one to construct one. The vagaries of
the names of terms as he uses them allow such latitude in interpretation that
modern scientists are not agreed as to the practicability of Bacon's
suggestions. For example, he constantly refers to force under such names as
virtus, species, imago, agentis, and a score of other names, and this
naturally gives rise to the great differences in the interpretations of his
writings, with corresponding differences in estimates of them.
The claim that Bacon originated the use of lenses, in the form of
spectacles, cannot be proven. Smith has determined that as early as the
opening years of the fourteenth century such lenses were in use, but this
proves nothing as regards Bacon's connection with their invention. The
knowledge of lenses seems to be very ancient, if we may judge from the
convex lens of rock crystal found by Layard in his excavations at Nimrud.
There is nothing to show, however, that the ancients ever thought of using
them to correct defects of vision. Neither, apparently, is it feasible to
determine whether the idea of such an application originated with Bacon.
Another mechanical discovery about which there has been a great deal of
discussion is Bacon's supposed invention of gunpowder. It appears that in a
certain passage of his work he describes the process of making a substance
that is, in effect, ordinary gunpowder; but it is more than doubtful whether
he understood the properties of the substance he describes. It is fairly well
established, however, that in Bacon's time gunpowder was known to the
Arabs, so that it should not be surprising to find references made to it in
Bacon's work, since there is reason to believe that he constantly consulted
Arabian writings.
The great merit of Bacon's work, however, depends on the principles
taught as regards experiment and the observation of nature, rather than on
any single invention. He had the all-important idea of breaking with
tradition. He championed unfettered inquiry in every field of thought. He
had the instinct of a scientific worker—a rare instinct indeed in that age.
Nor need we doubt that to the best of his opportunities he was himself an
original investigator.
LEONARDO DA VINCI

The relative infertility of Bacon's thought is shown by the fact that he
founded no school and left no trace of discipleship. The entire century after
his death shows no single European name that need claim the attention of
the historian of science. In the latter part of the fifteenth century, however,
there is evidence of a renaissance of science no less than of art. The German
Muller became famous under the latinized named of Regio Montanus
(1437-1472), although his actual scientific attainments would appear to
have been important only in comparison with the utter ignorance of his
contemporaries. The most distinguished worker of the new era was the
famous Italian Leonardo da Vinci—a man who has been called by
Hamerton the most universal genius that ever lived. Leonardo's position in
the history of art is known to every one. With that, of course, we have no
present concern; but it is worth our while to inquire at some length as to the
famous painter's accomplishments as a scientist.
From a passage in the works of Leonardo, first brought to light by
Venturi,(1) it would seem that the great painter anticipated Copernicus in
determining the movement of the earth. He made mathematical calculations
to prove this, and appears to have reached the definite conclusion that the
earth does move—or what amounts to the same thing, that the sun does not
move. Muntz is authority for the statement that in one of his writings he
declares, "Il sole non si mouve"—the sun does not move.(2)
Among his inventions is a dynamometer for determining the traction
power of machines and animals, and his experiments with steam have led
some of his enthusiastic partisans to claim for him priority to Watt in the
invention of the steam-engine. In these experiments, however, Leonardo
seems to have advanced little beyond Hero of Alexandria and his steam toy.
Hero's steam-engine did nothing but rotate itself by virtue of escaping jets
of steam forced from the bent tubes, while Leonardo's "steam-engine"
"drove a ball weighing one talent over a distance of six stadia." In a
manuscript now in the library of the Institut de France, Da Vinci describes
this engine minutely. The action of this machine was due to the sudden
conversion of small quantities of water into steam ("smoke," as he called it)
by coming suddenly in contact with a heated surface in a proper receptacle,
the rapidly formed steam acting as a propulsive force after the manner of an
explosive. It is really a steam-gun, rather than a steam-engine, and it is not
unlikely that the study of the action of gunpowder may have suggested it to
Leonardo.

It is believed that Leonardo is the true discoverer of the camera-obscura,
although the Neapolitan philosopher, Giambattista Porta, who was not born
until some twenty years after the death of Leonardo, is usually credited with
first describing this device. There is little doubt, however, that Da Vinci
understood the principle of this mechanism, for he describes how such a
camera can be made by cutting a small, round hole through the shutter of a
darkened room, the reversed image of objects outside being shown on the
opposite wall.
Like other philosophers in all ages, he had observed a great number of
facts which he was unable to explain correctly. But such accumulations of
scientific observations are always interesting, as showing how many
centuries of observation frequently precede correct explanation. He
observed many facts about sounds, among others that blows struck upon a
bell produced sympathetic sounds in a bell of the same kind; and that
striking the string of a lute produced vibration in corresponding strings of
lutes strung to the same pitch. He knew, also, that sounds could be heard at
a distance at sea by listening at one end of a tube, the other end of which
was placed in the water; and that the same expedient worked successfully
on land, the end of the tube being placed against the ground.
The knowledge of this great number of unexplained facts is often
interpreted by the admirers of Da Vinci, as showing an almost occult insight
into science many centuries in advance of his time. Such interpretations,
however, are illusive. The observation, for example, that a tube placed
against the ground enables one to hear movements on the earth at a
distance, is not in itself evidence of anything more than acute scientific
observation, as a similar method is in use among almost every race of
savages, notably the American Indians. On the other hand, one is inclined to
give credence to almost any story of the breadth of knowledge of the man
who came so near anticipating Hutton, Lyell, and Darwin in his
interpretation of the geological records as he found them written on the
rocks.
It is in this field of geology that Leonardo is entitled to the greatest
admiration by modern scientists. He had observed the deposit of fossil
shells in various strata of rocks, even on the tops of mountains, and he
rejected once for all the theory that they had been deposited there by the
Deluge. He rightly interpreted their presence as evidence that they had once

been deposited at the bottom of the sea. This process he assumed bad taken
hundreds and thousands of centuries, thus tacitly rejecting the biblical
tradition as to the date of the creation.
Notwithstanding the obvious interest that attaches to the investigations of
Leonardo, it must be admitted that his work in science remained almost as
infertile as that of his great precursor, Bacon. The really stimulative work of
this generation was done by a man of affairs, who knew little of theoretical
science except in one line, but who pursued that one practical line until he
achieved a wonderful result. This man was Christopher Columbus. It is not
necessary here to tell the trite story of his accomplishment. Suffice it that
his practical demonstration of the rotundity of the earth is regarded by most
modern writers as marking an epoch in history. With the year of his voyage
the epoch of the Middle Ages is usually regarded as coming to an end. It
must not be supposed that any very sudden change came over the aspect of
scholarship of the time, but the preliminaries of great things had been
achieved, and when Columbus made his famous voyage in 1492, the man
was already alive who was to bring forward the first great vitalizing thought
in the field of pure science that the Western world had originated for more
than a thousand years. This man bore the name of Kopernik, or in its
familiar Anglicized form, Copernicus. His life work and that of his disciples
will claim our attention in the succeeding chapter.

IV. THE NEW COSMOLOGY—COPERNICUS
TO KEPLER AND GALILEO
We have seen that the Ptolemaic astronomy, which was the accepted
doctrine throughout the Middle Ages, taught that the earth is round.
Doubtless there was a popular opinion current which regarded the earth as
flat, but it must be understood that this opinion had no champions among
men of science during the Middle Ages. When, in the year 1492, Columbus
sailed out to the west on his memorable voyage, his expectation of reaching
India had full scientific warrant, however much it may have been scouted
by certain ecclesiastics and by the average man of the period. Nevertheless,
we may well suppose that the successful voyage of Columbus, and the still
more demonstrative one made about thirty years later by Magellan, gave the
theory of the earth's rotundity a certainty it could never previously have
had. Alexandrian geographers had measured the size of the earth, and had
not hesitated to assert that by sailing westward one might reach India. But
there is a wide gap between theory and practice, and it required the voyages
of Columbus and his successors to bridge that gap.
After the companions of Magellan completed the circumnavigation of the
globe, the general shape of our earth would, obviously, never again be
called in question. But demonstration of the sphericity of the earth had, of
course, no direct bearing upon the question of the earth's position in the
universe. Therefore the voyage of Magellan served to fortify, rather than to
dispute, the Ptolemaic theory. According to that theory, as we have seen, the
earth was supposed to lie immovable at the centre of the universe; the
various heavenly bodies, including the sun, revolving about it in eccentric
circles. We have seen that several of the ancient Greeks, notably
Aristarchus, disputed this conception, declaring for the central position of
the sun in the universe, and the motion of the earth and other planets about
that body. But this revolutionary theory seemed so opposed to the ordinary
observation that, having been discountenanced by Hipparchus and Ptolemy,
it did not find a single important champion for more than a thousand years
after the time of the last great Alexandrian astronomer.

The first man, seemingly, to hark back to the Aristarchian conception in
the new scientific era that was now dawning was the noted cardinal,
Nikolaus of Cusa, who lived in the first half of the fifteenth century, and
was distinguished as a philosophical writer and mathematician. His De
Docta Ignorantia expressly propounds the doctrine of the earth's motion. No
one, however, paid the slightest attention to his suggestion, which,
therefore, merely serves to furnish us with another interesting illustration of
the futility of propounding even a correct hypothesis before the time is ripe
to receive it—particularly if the hypothesis is not fully fortified by
reasoning based on experiment or observation.
The man who was destined to put forward the theory of the earth's
motion in a way to command attention was born in 1473, at the village of
Thorn, in eastern Prussia. His name was Nicholas Copernicus. There is no
more famous name in the entire annals of science than this, yet posterity has
never been able fully to establish the lineage of the famous expositor of the
true doctrine of the solar system. The city of Thorn lies in a province of that
border territory which was then under control of Poland, but which
subsequently became a part of Prussia. It is claimed that the aspects of the
city were essentially German, and it is admitted that the mother of
Copernicus belonged to that race. The nationality of the father is more in
doubt, but it is urged that Copernicus used German as his mother-tongue.
His great work was, of course, written in Latin, according to the custom of
the time; but it is said that, when not employing that language, he always
wrote in German. The disputed nationality of Copernicus strongly suggests
that he came of a mixed racial lineage, and we are reminded again of the
influences of those ethnical minglings to which we have previously more
than once referred. The acknowledged centres of civilization towards the
close of the fifteenth century were Italy and Spain. Therefore, the birthplace
of Copernicus lay almost at the confines of civilization, reminding us of that
earlier period when Greece was the centre of culture, but when the great
Greek thinkers were born in Asia Minor and in Italy.
As a young man, Copernicus made his way to Vienna to study medicine,
and subsequently he journeyed into Italy and remained there many years,
About the year 1500 he held the chair of mathematics in a college at Rome.
Subsequently he returned to his native land and passed his remaining years
there, dying at Domkerr, in Frauenburg, East Prussia, in the year 1543.

It would appear that Copernicus conceived the idea of the heliocentric
system of the universe while he was a comparatively young man, since in
the introduction to his great work, which he addressed to Pope Paul III., he
states that he has pondered his system not merely nine years, in accordance
with the maxim of Horace, but well into the fourth period of nine years.
Throughout a considerable portion of this period the great work of
Copernicus was in manuscript, but it was not published until the year of his
death. The reasons for the delay are not very fully established. Copernicus
undoubtedly taught his system throughout the later decades of his life. He
himself tells us that he had even questioned whether it were not better for
him to confine himself to such verbal teaching, following thus the example
of Pythagoras. Just as his life was drawing to a close, he decided to pursue
the opposite course, and the first copy of his work is said to have been
placed in his hands as he lay on his deathbed.
The violent opposition which the new system met from ecclesiastical
sources led subsequent commentators to suppose that Copernicus had
delayed publication of his work through fear of the church authorities.
There seems, however, to be no direct evidence for this opinion. It has been
thought significant that Copernicus addressed his work to the pope. It is, of
course, quite conceivable that the aged astronomer might wish by this
means to demonstrate that he wrote in no spirit of hostility to the church.
His address to the pope might have been considered as a desirable shield
precisely because the author recognized that his work must needs meet with
ecclesiastical criticism. Be that as it may, Copernicus was removed by death
from the danger of attack, and it remained for his disciples of a later
generation to run the gauntlet of criticism and suffer the charges of heresy.
The work of Copernicus, published thus in the year 1543 at Nuremberg,
bears the title De Orbium Coelestium Revolutionibus.
It is not necessary to go into details as to the cosmological system which
Copernicus advocated, since it is familiar to every one. In a word, he
supposed the sun to be the centre of all the planetary motions, the earth
taking its place among the other planets, the list of which, as known at that
time, comprised Mercury, Venus, the Earth, Mars, Jupiter, and Saturn. The
fixed stars were alleged to be stationary, and it was necessary to suppose
that they are almost infinitely distant, inasmuch as they showed to the

observers of that time no parallax; that is to say, they preserved the same
apparent position when viewed from the opposite points of the earth's orbit.
But let us allow Copernicus to speak for himself regarding his system,
His exposition is full of interest. We quote first the introduction just referred
to, in which appeal is made directly to the pope.
"I can well believe, most holy father, that certain people, when they hear
of my attributing motion to the earth in these books of mine, will at once
declare that such an opinion ought to be rejected. Now, my own theories do
not please me so much as not to consider what others may judge of them.
Accordingly, when I began to reflect upon what those persons who accept
the stability of the earth, as confirmed by the opinion of many centuries,
would say when I claimed that the earth moves, I hesitated for a long time
as to whether I should publish that which I have written to demonstrate its
motion, or whether it would not be better to follow the example of the
Pythagoreans, who used to hand down the secrets of philosophy to their
relatives and friends only in oral form. As I well considered all this, I was
almost impelled to put the finished work wholly aside, through the scorn I
had reason to anticipate on account of the newness and apparent
contrariness to reason of my theory.
"My friends, however, dissuaded me from such a course and admonished
me that I ought to publish my book, which had lain concealed in my
possession not only nine years, but already into four times the ninth year.
Not a few other distinguished and very learned men asked me to do the
same thing, and told me that I ought not, on account of my anxiety, to delay
any longer in consecrating my work to the general service of
mathematicians.
"But your holiness will perhaps not so much wonder that I have dared to
bring the results of my night labors to the light of day, after having taken so
much care in elaborating them, but is waiting instead to hear how it entered
my mind to imagine that the earth moved, contrary to the accepted opinion
of mathematicians—nay, almost contrary to ordinary human understanding.
Therefore I will not conceal from your holiness that what moved me to
consider another way of reckoning the motions of the heavenly bodies was
nothing else than the fact that the mathematicians do not agree with one
another in their investigations. In the first place, they are so uncertain about
the motions of the sun and moon that they cannot find out the length of a

full year. In the second place, they apply neither the same laws of cause and
effect, in determining the motions of the sun and moon and of the five
planets, nor the same proofs. Some employ only concentric circles, others
use eccentric and epicyclic ones, with which, however, they do not fully
attain the desired end. They could not even discover nor compute the main
thing—namely, the form of the universe and the symmetry of its parts. It
was with them as if some should, from different places, take hands, feet,
head, and other parts of the body, which, although very beautiful, were not
drawn in their proper relations, and, without making them in any way
correspond, should construct a monster instead of a human being.
"Accordingly, when I had long reflected on this uncertainty of
mathematical tradition, I took the trouble to read again the books of all the
philosophers I could get hold of, to see if some one of them had not once
believed that there were other motions of the heavenly bodies. First I found
in Cicero that Niceties had believed in the motion of the earth. Afterwards I
found in Plutarch, likewise, that some others had held the same opinion.
This induced me also to begin to consider the movability of the earth, and,
although the theory appeared contrary to reason, I did so because I knew
that others before me had been allowed to assume rotary movements at will,
in order to explain the phenomena of these celestial bodies. I was of the
opinion that I, too, might be permitted to see whether, by presupposing
motion in the earth, more reliable conclusions than hitherto reached could
not be discovered for the rotary motions of the spheres. And thus, acting on
the hypothesis of the motion which, in the following book, I ascribe to the
earth, and by long and continued observations, I have finally discovered
that if the motion of the other planets be carried over to the relation of the
earth and this is made the basis for the rotation of every star, not only will
the phenomena of the planets be explained thereby, but also the laws and
the size of the stars; all their spheres and the heavens themselves will
appear so harmoniously connected that nothing could be changed in any
part of them without confusion in the remaining parts and in the whole
universe. I do not doubt that clever and learned men will agree with me if
they are willing fully to comprehend and to consider the proofs which I
advance in the book before us. In order, however, that both the learned and
the unlearned may see that I fear no man's judgment, I wanted to dedicate
these, my night labors, to your holiness, rather than to any one else, because
you, even in this remote corner of the earth where I live, are held to be the

greatest in dignity of station and in love for all sciences and for
mathematics, so that you, through your position and judgment, can easily
suppress the bites of slanderers, although the proverb says that there is no
remedy against the bite of calumny."
In chapter X. of book I., "On the Order of the Spheres," occurs a more
detailed presentation of the system, as follows:
"That which Martianus Capella, and a few other Latins, very well knew,
appears to me extremely noteworthy. He believed that Venus and Mercury
revolve about the sun as their centre and that they cannot go farther away
from it than the circles of their orbits permit, since they do not revolve
about the earth like the other planets. According to this theory, then,
Mercury's orbit would be included within that of Venus, which is more than
twice as great, and would find room enough within it for its revolution.
"If, acting upon this supposition, we connect Saturn, Jupiter, and Mars
with the same centre, keeping in mind the greater extent of their orbits,
which include the earth's sphere besides those of Mercury and Venus, we
cannot fail to see the explanation of the regular order of their motions. He is
certain that Saturn, Jupiter, and Mars are always nearest the earth when they
rise in the evening—that is, when they appear over against the sun, or the
earth stands between them and the sun—but that they are farthest from the
earth when they set in the evening—that is, when we have the sun between
them and the earth. This proves sufficiently that their centre belongs to the
sun and is the same about which the orbits of Venus and Mercury circle.
Since, however, all have one centre, it is necessary for the space intervening
between the orbits of Venus and Mars to include the earth with her
accompanying moon and all that is beneath the moon; for the moon, which
stands unquestionably nearest the earth, can in no way be separated from
her, especially as there is sufficient room for the moon in the aforesaid
space. Hence we do not hesitate to claim that the whole system, which
includes the moon with the earth for its centre, makes the round of that
great circle between the planets, in yearly motion about the sun, and
revolves about the centre of the universe, in which the sun rests motionless,
and that all which looks like motion in the sun is explained by the motion of
the earth. The extent of the universe, however, is so great that, whereas the
distance of the earth from the sun is considerable in comparison with the
size of the other planetary orbits, it disappears when compared with the

sphere of the fixed stars. I hold this to be more easily comprehensible than
when the mind is confused by an almost endless number of circles, which is
necessarily the case with those who keep the earth in the middle of the
universe. Although this may appear incomprehensible and contrary to the
opinion of many, I shall, if God wills, make it clearer than the sun, at least
to those who are not ignorant of mathematics.
"The order of the spheres is as follows: The first and lightest of all the
spheres is that of the fixed stars, which includes itself and all others, and
hence is motionless as the place in the universe to which the motion and
position of all other stars is referred.
"Then follows the outermost planet, Saturn, which completes its
revolution around the sun in thirty years; next comes Jupiter with a twelve
years' revolution; then Mars, which completes its course in two years. The
fourth one in order is the yearly revolution which includes the earth with the
moon's orbit as an epicycle. In the fifth place is Venus with a revolution of
nine months. The sixth place is taken by Mercury, which completes its
course in eighty days. In the middle of all stands the sun, and who could
wish to place the lamp of this most beautiful temple in another or better
place. Thus, in fact, the sun, seated upon the royal throne, controls the
family of the stars which circle around him. We find in their order a
harmonious connection which cannot be found elsewhere. Here the
attentive observer can see why the waxing and waning of Jupiter seems
greater than with Saturn and smaller than with Mars, and again greater with
Venus than with Mercury. Also, why Saturn, Jupiter, and Mars are nearer to
the earth when they rise in the evening than when they disappear in the rays
of the sun. More prominently, however, is it seen in the case of Mars, which
when it appears in the heavens at night, seems to equal Jupiter in size, but
soon afterwards is found among the stars of second magnitude. All of this
results from the same cause—namely, from the earth's motion. The fact that
nothing of this is to be seen in the case of the fixed stars is a proof of their
immeasurable distance, which makes even the orbit of yearly motion or its
counterpart invisible to us."(1)
The fact that the stars show no parallax had been regarded as an
important argument against the motion of the earth, and it was still so
considered by the opponents of the system of Copernicus. It had, indeed,
been necessary for Aristarchus to explain the fact as due to the extreme

distance of the stars; a perfectly correct explanation, but one that implies
distances that are altogether inconceivable. It remained for nineteenth-
century astronomers to show, with the aid of instruments of greater
precision, that certain of the stars have a parallax. But long before this
demonstration had been brought forward, the system of Copernicus had
been accepted as a part of common knowledge.
While Copernicus postulated a cosmical scheme that was correct as to its
main features, he did not altogether break away from certain defects of the
Ptolemaic hypothesis. Indeed, he seems to have retained as much of this as
practicable, in deference to the prejudice of his time. Thus he records the
planetary orbits as circular, and explains their eccentricities by resorting to
the theory of epicycles, quite after the Ptolemaic method. But now, of
course, a much more simple mechanism sufficed to explain the planetary
motions, since the orbits were correctly referred to the central sun and not
to the earth.
Needless to say, the revolutionary conception of Copernicus did not meet
with immediate acceptance. A number of prominent astronomers, however,
took it up almost at once, among these being Rhaeticus, who wrote a
commentary on the evolutions; Erasmus Reinhold, the author of the
Prutenic tables; Rothmann, astronomer to the Landgrave of Hesse, and
Maestlin, the instructor of Kepler. The Prutenic tables, just referred to, so
called because of their Prussian origin, were considered an improvement on
the tables of Copernicus, and were highly esteemed by the astronomers of
the time. The commentary of Rhaeticus gives us the interesting information
that it was the observation of the orbit of Mars and of the very great
difference between his apparent diameters at different times which first led
Copernicus to conceive the heliocentric idea. Of Reinhold it is recorded that
he considered the orbit of Mercury elliptical, and that he advocated a theory
of the moon, according to which her epicycle revolved on an elliptical orbit,
thus in a measure anticipating one of the great discoveries of Kepler to
which we shall refer presently. The Landgrave of Hesse was a practical
astronomer, who produced a catalogue of fixed stars which has been
compared with that of Tycho Brahe. He was assisted by Rothmann and by
Justus Byrgius. Maestlin, the preceptor of Kepler, is reputed to have been
the first modern observer to give a correct explanation of the light seen on
portions of the moon not directly illumined by the sun. He explained this as
not due to any proper light of the moon itself, but as light reflected from the

earth. Certain of the Greek philosophers, however, are said to have given
the same explanation, and it is alleged also that Leonardo da Vinci
anticipated Maestlin in this regard.(2)
While, various astronomers of some eminence thus gave support to the
Copernican system, almost from the beginning, it unfortunately chanced
that by far the most famous of the immediate successors of Copernicus
declined to accept the theory of the earth's motion. This was Tycho Brahe,
one of the greatest observing astronomers of any age. Tycho Brahe was a
Dane, born at Knudstrup in the year 1546. He died in 1601 at Prague, in
Bohemia. During a considerable portion of his life he found a patron in
Frederick, King of Denmark, who assisted him to build a splendid
observatory on the Island of Huene. On the death of his patron Tycho
moved to Germany, where, as good luck would have it, he came in contact
with the youthful Kepler, and thus, no doubt, was instrumental in
stimulating the ambitions of one who in later years was to be known as a far
greater theorist than himself. As has been said, Tycho rejected the
Copernican theory of the earth's motion. It should be added, however, that
he accepted that part of the Copernican theory which makes the sun the
centre of all the planetary motions, the earth being excepted. He thus
developed a system of his own, which was in some sort a compromise
between the Ptolemaic and the Copernican systems. As Tycho conceived it,
the sun revolves about the earth, carrying with it the planets-Mercury,
Venus, Mars, Jupiter, and Saturn, which planets have the sun and not the
earth as the centre of their orbits. This cosmical scheme, it should be added,
may be made to explain the observed motions of the heavenly bodies, but it
involves a much more complex mechanism than is postulated by the
Copernican theory.
Various explanations have been offered of the conservatism which held
the great Danish astronomer back from full acceptance of the relatively
simple and, as we now know, correct Copernican doctrine. From our latter-
day point of view, it seems so much more natural to accept than to reject the
Copernican system, that we find it difficult to put ourselves in the place of a
sixteenth-century observer. Yet if we recall that the traditional view, having
warrant of acceptance by nearly all thinkers of every age, recorded the earth
as a fixed, immovable body, we shall see that our surprise should be excited
rather by the thinker who can break away from this view than by the one
who still tends to cling to it.

Moreover, it is useless to attempt to disguise the fact that something more
than a mere vague tradition was supposed to support the idea of the earth's
overshadowing importance in the cosmical scheme. The sixteenth-century
mind was overmastered by the tenets of ecclesiasticism, and it was a
dangerous heresy to doubt that the Hebrew writings, upon which
ecclesiasticism based its claim, contained the last word regarding matters of
science. But the writers of the Hebrew text had been under the influence of
that Babylonian conception of the universe which accepted the earth as
unqualifiedly central—which, indeed, had never so much as conceived a
contradictory hypothesis; and so the Western world, which had come to
accept these writings as actually supernatural in origin, lay under the spell
of Oriental ideas of a pre-scientific era. In our own day, no one speaking
with authority thinks of these Hebrew writings as having any scientific
weight whatever. Their interest in this regard is purely antiquarian; hence
from our changed point of view it seems scarcely credible that Tycho Brahe
can have been in earnest when he quotes the Hebrew traditions as proof that
the sun revolves about the earth. Yet we shall see that for almost three
centuries after the time of Tycho, these same dreamings continued to be
cited in opposition to those scientific advances which new observations
made necessary; and this notwithstanding the fact that the Oriental phrasing
is, for the most part, poetically ambiguous and susceptible of shifting
interpretations, as the criticism of successive generations has amply
testified.
As we have said, Tycho Brahe, great observer as he was, could not shake
himself free from the Oriental incubus. He began his objections, then, to the
Copernican system by quoting the adverse testimony of a Hebrew prophet
who lived more than a thousand years B.C. All of this shows sufficiently
that Tycho Brahe was not a great theorist. He was essentially an observer,
but in this regard he won a secure place in the very first rank. Indeed, he
was easily the greatest observing astronomer since Hipparchus, between
whom and himself there were many points of resemblance. Hipparchus, it
will be recalled, rejected the Aristarchian conception of the universe just as
Tycho rejected the conception of Copernicus.
But if Tycho propounded no great generalizations, the list of specific
advances due to him is a long one, and some of these were to prove
important aids in the hands of later workers to the secure demonstration of
the Copernican idea. One of his most important series of studies had to do

with comets. Regarding these bodies there had been the greatest uncertainty
in the minds of astronomers. The greatest variety of opinions regarding
them prevailed; they were thought on the one hand to be divine messengers,
and on the other to be merely igneous phenomena of the earth's atmosphere.
Tycho Brahe declared that a comet which he observed in the year 1577 had
no parallax, proving its extreme distance. The observed course of the comet
intersected the planetary orbits, which fact gave a quietus to the long-
mooted question as to whether the Ptolemaic spheres were transparent
solids or merely imaginary; since the comet was seen to intersect these
alleged spheres, it was obvious that they could not be the solid substance
that they were commonly imagined to be, and this fact in itself went far
towards discrediting the Ptolemaic system. It should be recalled, however,
that this supposition of tangible spheres for the various planetary and stellar
orbits was a mediaeval interpretation of Ptolemy's theory rather than an
interpretation of Ptolemy himself, there being nothing to show that the
Alexandrian astronomer regarded his cycles and epicycles as other than
theoretical.
An interesting practical discovery made by Tycho was his method of
determining the latitude of a place by means of two observations made at an
interval of twelve hours. Hitherto it had been necessary to observe the sun's
angle on the equinoctial days, a period of six months being therefore
required. Tycho measured the angle of elevation of some star situated near
the pole, when on the meridian, and then, twelve hours later, measured the
angle of elevation of the same star when it again came to the meridian at the
opposite point of its apparent circle about the polestar. Half the sum of these
angles gives the latitude of the place of observation.
As illustrating the accuracy of Tycho's observations, it may be noted that
he rediscovered a third inequality of the moon's motion at its variation, he,
in common with other European astronomers, being then quite unaware that
this inequality had been observed by an Arabian astronomer. Tycho proved
also that the angle of inclination of the moon's orbit to the ecliptic is subject
to slight variation.
The very brilliant new star which shone forth suddenly in the
constellation of Cassiopeia in the year 1572, was made the object of special
studies by Tycho, who proved that the star had no sensible parallax and
consequently was far beyond the planetary regions. The appearance of a

new star was a phenomenon not unknown to the ancients, since Pliny
records that Hipparchus was led by such an appearance to make his
catalogue of the fixed stars. But the phenomenon is sufficiently uncommon
to attract unusual attention. A similar phenomenon occurred in the year
1604, when the new star—in this case appearing in the constellation of
Serpentarius—was explained by Kepler as probably proceeding from a vast
combustion. This explanation—in which Kepler is said to have followed.
Tycho—is fully in accord with the most recent theories on the subject, as
we shall see in due course. It is surprising to hear Tycho credited with so
startling a theory, but, on the other hand, such an explanation is precisely
what should be expected from the other astronomer named. For Johann
Kepler, or, as he was originally named, Johann von Kappel, was one of the
most speculative astronomers of any age. He was forever theorizing, but
such was the peculiar quality of his mind that his theories never satisfied
him for long unless he could put them to the test of observation. Thanks to
this happy combination of qualities, Kepler became the discoverer of three
famous laws of planetary motion which lie at the very foundation of
modern astronomy, and which were to be largely instrumental in guiding
Newton to his still greater generalization. These laws of planetary motion
were vastly important as corroborating the Copernican theory of the
universe, though their position in this regard was not immediately
recognized by contemporary thinkers. Let us examine with some detail into
their discovery, meantime catching a glimpse of the life history of the
remarkable man whose name they bear.
JOHANN KEPLER AND THE LAWS OF PLANETARY MOTION
Johann Kepler was born the 27th of December, 1571, in the little town of
Weil, in Wurtemburg. He was a weak, sickly child, further enfeebled by a
severe attack of small-pox. It would seem paradoxical to assert that the
parents of such a genius were mismated, but their home was not a happy
one, the mother being of a nervous temperament, which perhaps in some
measure accounted for the genius of the child. The father led the life of a
soldier, and finally perished in the campaign against the Turks. Young
Kepler's studies were directed with an eye to the ministry. After a
preliminary training he attended the university at Tubingen, where he came
under the influence of the celebrated Maestlin and became his life-long
friend.

Curiously enough, it is recorded that at first Kepler had no taste for
astronomy or for mathematics. But the doors of the ministry being presently
barred to him, he turned with enthusiasm to the study of astronomy, being
from the first an ardent advocate of the Copernican system. His teacher,
Maestlin, accepted the same doctrine, though he was obliged, for
theological reasons, to teach the Ptolemaic system, as also to oppose the
Gregorian reform of the calendar.
The Gregorian calendar, it should be explained, is so called because it
was instituted by Pope Gregory XIII., who put it into effect in the year
1582, up to which time the so-called Julian calendar, as introduced by Julius
Caesar, had been everywhere accepted in Christendom. This Julian
calendar, as we have seen, was a great improvement on preceding ones, but
still lacked something of perfection inasmuch as its theoretical day differed
appreciably from the actual day. In the course of fifteen hundred years,
since the time of Caesar, this defect amounted to a discrepancy of about
eleven days. Pope Gregory proposed to correct this by omitting ten days
from the calendar, which was done in September, 1582. To prevent similar
inaccuracies in the future, the Gregorian calendar provided that once in four
centuries the additional day to make a leap-year should be omitted, the date
selected for such omission being the last year of every fourth century. Thus
the years 1500, 1900, and 2300, A.D., would not be leap-years. By this
arrangement an approximate rectification of the calendar was effected,
though even this does not make it absolutely exact.
Such a rectification as this was obviously desirable, but there was really
no necessity for the omission of the ten days from the calendar. The
equinoctial day had shifted so that in the year 1582 it fell on the 10th of
March and September. There was no reason why it should not have
remained there. It would greatly have simplified the task of future historians
had Gregory contented himself with providing for the future stability of the
calendar without making the needless shift in question. We are so
accustomed to think of the 21st of March and 21st of September as the
natural periods of the equinox, that we are likely to forget that these are
purely arbitrary dates for which the 10th might have been substituted
without any inconvenience or inconsistency.
But the opposition to the new calendar, to which reference has been
made, was not based on any such considerations as these. It was due,

largely at any rate, to the fact that Germany at this time was under sway of
the Lutheran revolt against the papacy. So effective was the opposition that
the Gregorian calendar did not come into vogue in Germany until the year
1699. It may be added that England, under stress of the same manner of
prejudice, held out against the new reckoning until the year 1751, while
Russia does not accept it even now.
As the Protestant leaders thus opposed the papal attitude in a matter of so
practical a character as the calendar, it might perhaps have been expected
that the Lutherans would have had a leaning towards the Copernican theory
of the universe, since this theory was opposed by the papacy. Such,
however, was not the case. Luther himself pointed out with great
strenuousness, as a final and demonstrative argument, the fact that Joshua
commanded the sun and not the earth to stand still; and his followers were
quite as intolerant towards the new teaching as were their ultramontane
opponents. Kepler himself was, at various times, to feel the restraint of
ecclesiastical opposition, though he was never subjected to direct
persecution, as was his friend and contemporary, Galileo. At the very outset
of Kepler's career there was, indeed, question as to the publication of a
work he had written, because that work took for granted the truth of the
Copernican doctrine. This work appeared, however, in the year 1596. It
bore the title Mysterium Cosmographium, and it attempted to explain the
positions of the various planetary bodies. Copernicus had devoted much
time to observation of the planets with reference to measuring their
distance, and his efforts had been attended with considerable success. He
did not, indeed, know the actual distance of the sun, and, therefore, was
quite unable to fix the distance of any planet; but, on the other hand, he
determined the relative distance of all the planets then known, as measured
in terms of the sun's distance, with remarkable accuracy.
With these measurements as a guide, Kepler was led to a very fanciful
theory, according to which the orbits of the five principal planets sustain a
peculiar relation to the five regular solids of geometry. His theory was this:
"Around the orbit of the earth describe a dodecahedron—the circle
comprising it will be that of Mars; around Mars describe a tetrahedron—the
circle comprising it will be that of Jupiter; around Jupiter describe a cube—
the circle comprising it will be that of Saturn; now within the earth's orbit
inscribe an icosahedron—the inscribed circle will be that of Venus; in the

orbit of Venus inscribe an octahedron—the circle inscribed will be that of
Mercury."(3)
Though this arrangement was a fanciful one, which no one would now
recall had not the theorizer obtained subsequent fame on more substantial
grounds, yet it evidenced a philosophical spirit on the part of the astronomer
which, misdirected as it was in this instance, promised well for the future.
Tycho Brahe, to whom a copy of the work was sent, had the acumen to
recognize it as a work of genius. He summoned the young astronomer to be
his assistant at Prague, and no doubt the association thus begun was
instrumental in determining the character of Kepler's future work. It was
precisely the training in minute observation that could avail most for a mind
which, like Kepler's, tended instinctively to the formulation of theories.
When Tycho Brahe died, in 1601, Kepler became his successor. In due time
he secured access to all the unpublished observations of his great
predecessor, and these were of inestimable value to him in the progress of
his own studies.
Kepler was not only an ardent worker and an enthusiastic theorizer, but
he was an indefatigable writer, and it pleased him to take the public fully
into his confidence, not merely as to his successes, but as to his failures.
Thus his works elaborate false theories as well as correct ones, and detail
the observations through which the incorrect guesses were refuted by their
originator. Some of these accounts are highly interesting, but they must not
detain us here. For our present purpose it must suffice to point out the three
important theories, which, as culled from among a score or so of incorrect
ones, Kepler was able to demonstrate to his own satisfaction and to that of
subsequent observers. Stated in a few words, these theories, which have
come to bear the name of Kepler's Laws, are the following:
1. That the planetary orbits are not circular, but elliptical, the sun
occupying one focus of the ellipses.
2. That the speed of planetary motion varies in different parts of the orbit
in such a way that an imaginary line drawn from the sun to the planet—that
is to say, the radius vector of the planet's orbit—always sweeps the same
area in a given time.
These two laws Kepler published as early as 1609. Many years more of
patient investigation were required before he found out the secret of the
relation between planetary distances and times of revolution which his third

law expresses. In 1618, however, he was able to formulate this relation also,
as follows:
3. The squares of the distance of the various planets from the sun are
proportional to the cubes of their periods of revolution about the sun.
All these laws, it will be observed, take for granted the fact that the sun is
the centre of the planetary orbits. It must be understood, too, that the earth
is constantly regarded, in accordance with the Copernican system, as being
itself a member of the planetary system, subject to precisely the same laws
as the other planets. Long familiarity has made these wonderful laws of
Kepler seem such a matter of course that it is difficult now to appreciate
them at their full value. Yet, as has been already pointed out, it was the
knowledge of these marvellously simple relations between the planetary
orbits that laid the foundation for the Newtonian law of universal
gravitation. Contemporary judgment could not, of course, anticipate this
culmination of a later generation. What it could understand was that the first
law of Kepler attacked one of the most time-honored of metaphysical
conceptions—namely, the Aristotelian idea that the circle is the perfect
figure, and hence that the planetary orbits must be circular. Not even
Copernicus had doubted the validity of this assumption. That Kepler dared
dispute so firmly fixed a belief, and one that seemingly had so sound a
philosophical basis, evidenced the iconoclastic nature of his genius. That he
did not rest content until he had demonstrated the validity of his
revolutionary assumption shows how truly this great theorizer made his
hypotheses subservient to the most rigid inductions.
GALILEO GALILEI
While Kepler was solving these riddles of planetary motion, there was an
even more famous man in Italy whose championship of the Copernican
doctrine was destined to give the greatest possible publicity to the new
ideas. This was Galileo Galilei, one of the most extraordinary scientific
observers of any age. Galileo was born at Pisa, on the 18th of February (old
style), 1564. The day of his birth is doubly memorable, since on the same
day the greatest Italian of the preceding epoch, Michael Angelo, breathed
his last. Persons fond of symbolism have found in the coincidence a
forecast of the transit from the artistic to the scientific epoch of the later
Renaissance. Galileo came of an impoverished noble family. He was
educated for the profession of medicine, but did not progress far before his

natural proclivities directed him towards the physical sciences. Meeting
with opposition in Pisa, he early accepted a call to the chair of natural
philosophy in the University of Padua, and later in life he made his home at
Florence. The mechanical and physical discoveries of Galileo will claim our
attention in another chapter. Our present concern is with his contribution to
the Copernican theory.
Galileo himself records in a letter to Kepler that he became a convert to
this theory at an early day. He was not enabled, however, to make any
marked contribution to the subject, beyond the influence of his general
teachings, until about the year 1610. The brilliant contributions which he
made were due largely to a single discovery—namely, that of the telescope.
Hitherto the astronomical observations had been made with the unaided
eye. Glass lenses had been known since the thirteenth century, but, until
now, no one had thought of their possible use as aids to distant vision. The
question of priority of discovery has never been settled. It is admitted,
however, that the chief honors belong to the opticians of the Netherlands.
As early as the year 1590 the Dutch optician Zacharias Jensen placed a
concave and a convex lens respectively at the ends of a tube about eighteen
inches long, and used this instrument for the purpose of magnifying small
objects—producing, in short, a crude microscope. Some years later,
Johannes Lippershey, of whom not much is known except that he died in
1619, experimented with a somewhat similar combination of lenses, and
made the startling observation that the weather-vane on a distant church-
steeple seemed to be brought much nearer when viewed through the lens.
The combination of lenses he employed is that still used in the construction
of opera-glasses; the Germans still call such a combination a Dutch
telescope.
Doubtless a large number of experimenters took the matter up and the
fame of the new instrument spread rapidly abroad. Galileo, down in Italy,
heard rumors of this remarkable contrivance, through the use of which it
was said "distant objects might be seen as clearly as those near at hand." He
at once set to work to construct for himself a similar instrument, and his
efforts were so far successful that at first he "saw objects three times as near
and nine times enlarged." Continuing his efforts, he presently so improved
his glass that objects were enlarged almost a thousand times and made to
appear thirty times nearer than when seen with the naked eye. Naturally

enough, Galileo turned this fascinating instrument towards the skies, and he
was almost immediately rewarded by several startling discoveries. At the
very outset, his magnifying-glass brought to view a vast number of stars
that are invisible to the naked eye, and enabled the observer to reach the
conclusion that the hazy light of the Milky Way is merely due to the
aggregation of a vast number of tiny stars.
Turning his telescope towards the moon, Galileo found that body rough
and earth-like in contour, its surface covered with mountains, whose height
could be approximately measured through study of their shadows. This was
disquieting, because the current Aristotelian doctrine supposed the moon, in
common with the planets, to be a perfectly spherical, smooth body. The
metaphysical idea of a perfect universe was sure to be disturbed by this
seemingly rough workmanship of the moon. Thus far, however, there was
nothing in the observations of Galileo to bear directly upon the Copernican
theory; but when an inspection was made of the planets the case was quite
different. With the aid of his telescope, Galileo saw that Venus, for example,
passes through phases precisely similar to those of the moon, due, of
course, to the same cause. Here, then, was demonstrative evidence that the
planets are dark bodies reflecting the light of the sun, and an explanation
was given of the fact, hitherto urged in opposition to the Copernican theory,
that the inferior planets do not seem many times brighter when nearer the
earth than when in the most distant parts of their orbits; the explanation
being, of course, that when the planets are between the earth and the sun
only a small portion of their illumined surfaces is visible from the earth.
On inspecting the planet Jupiter, a still more striking revelation was
made, as four tiny stars were observed to occupy an equatorial position near
that planet, and were seen, when watched night after night, to be circling
about the planet, precisely as the moon circles about the earth. Here,
obviously, was a miniature solar system—a tangible object-lesson in the
Copernican theory. In honor of the ruling Florentine house of the period,
Galileo named these moons of Jupiter, Medicean stars.
Turning attention to the sun itself, Galileo observed on the surface of that
luminary a spot or blemish which gradually changed its shape, suggesting
that changes were taking place in the substance of the sun—changes
obviously incompatible with the perfect condition demanded by the
metaphysical theorists. But however disquieting for the conservative, the

sun's spots served a most useful purpose in enabling Galileo to demonstrate
that the sun itself revolves on its axis, since a given spot was seen to pass
across the disk and after disappearing to reappear in due course. The period
of rotation was found to be about twenty-four days.
It must be added that various observers disputed priority of discovery of
the sun's spots with Galileo. Unquestionably a sun-spot had been seen by
earlier observers, and by them mistaken for the transit of an inferior planet.
Kepler himself had made this mistake. Before the day of the telescope, he
had viewed the image of the sun as thrown on a screen in a camera-obscura,
and had observed a spot on the disk which be interpreted as representing the
planet Mercury, but which, as is now known, must have been a sun-spot,
since the planetary disk is too small to have been revealed by this method.
Such observations as these, however interesting, cannot be claimed as
discoveries of the sun-spots. It is probable, however, that several
discoverers (notably Johann Fabricius) made the telescopic observation of
the spots, and recognized them as having to do with the sun's surface,
almost simultaneously with Galileo. One of these claimants was a Jesuit
named Scheiner, and the jealousy of this man is said to have had a share in
bringing about that persecution to which we must now refer.
There is no more famous incident in the history of science than the
heresy trial through which Galileo was led to the nominal renunciation of
his cherished doctrines. There is scarcely another incident that has been
commented upon so variously. Each succeeding generation has put its own
interpretation on it. The facts, however, have been but little questioned. It
appears that in the year 1616 the church became at last aroused to the
implications of the heliocentric doctrine of the universe. Apparently it
seemed clear to the church authorities that the authors of the Bible believed
the world to be immovably fixed at the centre of the universe. Such, indeed,
would seem to be the natural inference from various familiar phrases of the
Hebrew text, and what we now know of the status of Oriental science in
antiquity gives full warrant to this interpretation. There is no reason to
suppose that the conception of the subordinate place of the world in the
solar system had ever so much as occurred, even as a vague speculation, to
the authors of Genesis. In common with their contemporaries, they believed
the earth to be the all-important body in the universe, and the sun a
luminary placed in the sky for the sole purpose of giving light to the earth.
There is nothing strange, nothing anomalous, in this view; it merely reflects

the current notions of Oriental peoples in antiquity. What is strange and
anomalous is the fact that the Oriental dreamings thus expressed could have
been supposed to represent the acme of scientific knowledge. Yet such a
hold had these writings taken upon the Western world that not even a
Galileo dared contradict them openly; and when the church fathers gravely
declared the heliocentric theory necessarily false, because contradictory to
Scripture, there were probably few people in Christendom whose mental
attitude would permit them justly to appreciate the humor of such a
pronouncement. And, indeed, if here and there a man might have risen to
such an appreciation, there were abundant reasons for the repression of the
impulse, for there was nothing humorous about the response with which the
authorities of the time were wont to meet the expression of iconoclastic
opinions. The burning at the stake of Giordano Bruno, in the year 1600,
was, for example, an object-lesson well calculated to restrain the
enthusiasm of other similarly minded teachers.
Doubtless it was such considerations that explained the relative silence of
the champions of the Copernican theory, accounting for the otherwise
inexplicable fact that about eighty years elapsed after the death of
Copernicus himself before a single text-book expounded his theory. The
text-book which then appeared, under date of 1622, was written by the
famous Kepler, who perhaps was shielded in a measure from the papal
consequences of such hardihood by the fact of residence in a Protestant
country. Not that the Protestants of the time favored the heliocentric
doctrine—we have already quoted Luther in an adverse sense—but of
course it was characteristic of the Reformation temper to oppose any papal
pronouncement, hence the ultramontane declaration of 1616 may indirectly
have aided the doctrine which it attacked, by making that doctrine less
obnoxious to Lutheran eyes. Be that as it may, the work of Kepler brought
its author into no direct conflict with the authorities. But the result was
quite different when, in 1632, Galileo at last broke silence and gave the
world, under cover of the form of dialogue, an elaborate exposition of the
Copernican theory. Galileo, it must be explained, had previously been
warned to keep silent on the subject, hence his publication doubly offended
the authorities. To be sure, he could reply that his dialogue introduced a
champion of the Ptolemaic system to dispute with the upholder of the
opposite view, and that, both views being presented with full array of
argument, the reader was left to reach a verdict for himself, the author

having nowhere pointedly expressed an opinion. But such an argument, of
course, was specious, for no one who read the dialogue could be in doubt as
to the opinion of the author. Moreover, it was hinted that Simplicio, the
character who upheld the Ptolemaic doctrine and who was everywhere
worsted in the argument, was intended to represent the pope himself—a
suggestion which probably did no good to Galileo's cause.
The character of Galileo's artistic presentation may best be judged from
an example, illustrating the vigorous assault of Salviati, the champion of the
new theory, and the feeble retorts of his conservative antagonist:
"Salviati. Let us then begin our discussion with the consideration that,
whatever motion may be attributed to the earth, yet we, as dwellers upon it,
and hence as participators in its motion, cannot possibly perceive anything
of it, presupposing that we are to consider only earthly things. On the other
hand, it is just as necessary that this same motion belong apparently to all
other bodies and visible objects, which, being separated from the earth, do
not take part in its motion. The correct method to discover whether one can
ascribe motion to the earth, and what kind of motion, is, therefore, to
investigate and observe whether in bodies outside the earth a perceptible
motion may be discovered which belongs to all alike. Because a movement
which is perceptible only in the moon, for instance, and has nothing to do
with Venus or Jupiter or other stars, cannot possibly be peculiar to the earth,
nor can its seat be anywhere else than in the moon. Now there is one such
universal movement which controls all others—namely, that which the sun,
moon, the other planets, the fixed stars—in short, the whole universe, with
the single exception of the earth—appears to execute from east to west in
the space of twenty-four hours. This now, as it appears at the first glance
anyway, might just as well be a motion of the earth alone as of all the rest of
the universe with the exception of the earth, for the same phenomena would
result from either hypothesis. Beginning with the most general, I will
enumerate the reasons which seem to speak in favor of the earth's motion.
When we merely consider the immensity of the starry sphere in comparison
with the smallness of the terrestrial ball, which is contained many million
times in the former, and then think of the rapidity of the motion which
completes a whole rotation in one day and night, I cannot persuade myself
how any one can hold it to be more reasonable and credible that it is the
heavenly sphere which rotates, while the earth stands still.

"Simplicio. I do not well understand how that powerful motion may be
said to as good as not exist for the sun, the moon, the other planets, and the
innumerable host of fixed stars. Do you call that nothing when the sun goes
from one meridian to another, rises up over this horizon and sinks behind
that one, brings now day, and now night; when the moon goes through
similar changes, and the other planets and fixed stars in the same way?
"Salviati. All the changes you mention are such only in respect to the
earth. To convince yourself of it, only imagine the earth out of existence.
There would then be no rising and setting of the sun or of the moon, no
horizon, no meridian, no day, no night—in short, the said motion causes no
change of any sort in the relation of the sun to the moon or to any of the
other heavenly bodies, be they planets or fixed stars. All changes are rather
in respect to the earth; they may all be reduced to the simple fact that the
sun is first visible in China, then in Persia, afterwards in Egypt, Greece,
France, Spain, America, etc., and that the same thing happens with the
moon and the other heavenly bodies. Exactly the same thing happens and in
exactly the same way if, instead of disturbing so large a part of the universe,
you let the earth revolve about itself. The difficulty is, however, doubled,
inasmuch as a second very important problem presents itself. If, namely,
that powerful motion is ascribed to the heavens, it is absolutely necessary to
regard it as opposed to the individual motion of all the planets, every one of
which indubitably has its own very leisurely and moderate movement from
west to east. If, on the other hand, you let the earth move about itself, this
opposition of motion disappears.
"The improbability is tripled by the complete overthrow of that order
which rules all the heavenly bodies in which the revolving motion is
definitely established. The greater the sphere is in such a case, so much
longer is the time required for its revolution; the smaller the sphere the
shorter the time. Saturn, whose orbit surpasses those of all the planets in
size, traverses it in thirty years. Jupiter(4) completes its smaller course in
twelve years, Mars in two; the moon performs its much smaller revolution
within a month. Just as clearly in the Medicean stars, we see that the one
nearest Jupiter completes its revolution in a very short time—about forty-
two hours; the next in about three and one-half days, the third in seven, and
the most distant one in sixteen days. This rule, which is followed
throughout, will still remain if we ascribe the twenty-four-hourly motion to
a rotation of the earth. If, however, the earth is left motionless, we must go

first from the very short rule of the moon to ever greater ones—to the two-
yearly rule of Mars, from that to the twelve-yearly one of Jupiter, from here
to the thirty-yearly one of Saturn, and then suddenly to an incomparably
greater sphere, to which also we must ascribe a complete rotation in twenty-
four hours. If, however, we assume a motion of the earth, the rapidity of the
periods is very well preserved; from the slowest sphere of Saturn we come
to the wholly motionless fixed stars. We also escape thereby a fourth
difficulty, which arises as soon as we assume that there is motion in the
sphere of the stars. I mean the great unevenness in the movement of these
very stars, some of which would have to revolve with extraordinary rapidity
in immense circles, while others moved very slowly in small circles, since
some of them are at a greater, others at a less, distance from the pole. That
is likewise an inconvenience, for, on the one hand, we see all those stars,
the motion of which is indubitable, revolve in great circles, while, on the
other hand, there seems to be little object in placing bodies, which are to
move in circles, at an enormous distance from the centre and then let them
move in very small circles. And not only are the size of the different circles
and therewith the rapidity of the movement very different in the different
fixed stars, but the same stars also change their orbits and their rapidity of
motion. Therein consists the fifth inconvenience. Those stars, namely,
which were at the equator two thousand years ago, and hence described
great circles in their revolutions, must to-day move more slowly and in
smaller circles, because they are many degrees removed from it. It will even
happen, after not so very long a time, that one of those which have hitherto
been continually in motion will finally coincide with the pole and stand
still, but after a period of repose will again begin to move. The other stars in
the mean while, which unquestionably move, all have, as was said, a great
circle for an orbit and keep this unchangeably.
"The improbability is further increased—this may be considered the sixth
inconvenience—by the fact that it is impossible to conceive what degree of
solidity those immense spheres must have, in the depths of which so many
stars are fixed so enduringly that they are kept revolving evenly in spite of
such difference of motion without changing their respective positions. Or if,
according to the much more probable theory, the heavens are fluid, and
every star describes an orbit of its own, according to what law then, or for
what reason, are their orbits so arranged that, when looked at from the
earth, they appear to be contained in one single sphere? To attain this it

seems to me much easier and more convenient to make them motionless
instead of moving, just as the paving-stones on the market-place, for
instance, remain in order more easily than the swarms of children running
about on them.
"Finally, the seventh difficulty: If we attribute the daily rotation to the
higher region of the heavens, we should have to endow it with force and
power sufficient to carry with it the innumerable host of the fixed stars—
every one a body of very great compass and much larger than the earth—
and all the planets, although the latter, like the earth, move naturally in an
opposite direction. In the midst of all this the little earth, single and alone,
would obstinately and wilfully withstand such force—a supposition which,
it appears to me, has much against it. I could also not explain why the earth,
a freely poised body, balancing itself about its centre, and surrounded on all
sides by a fluid medium, should not be affected by the universal rotation.
Such difficulties, however, do not confront us if we attribute motion to the
earth—such a small, insignificant body in comparison with the whole
universe, and which for that very reason cannot exercise any power over the
latter.
"Simplicio. You support your arguments throughout, it seems to me, on
the greater ease and simplicity with which the said effects are produced.
You mean that as a cause the motion of the earth alone is just as satisfactory
as the motion of all the rest of the universe with the exception of the earth;
you hold the actual event to be much easier in the former case than in the
latter. For the ruler of the universe, however, whose might is infinite, it is no
less easy to move the universe than the earth or a straw balm. But if his
power is infinite, why should not a greater, rather than a very small, part of
it be revealed to me?
"Salviati. If I had said that the universe does not move on account of the
impotence of its ruler, I should have been wrong and your rebuke would
have been in order. I admit that it is just as easy for an infinite power to
move a hundred thousand as to move one. What I said, however, does not
refer to him who causes the motion, but to that which is moved. In answer
to your remark that it is more fitting for an infinite power to reveal a large
part of itself rather than a little, I answer that, in relation to the infinite, one
part is not greater than another, if both are finite. Hence it is unallowable to
say that a hundred thousand is a larger part of an infinite number than two,

although the former is fifty thousand times greater than the latter. If,
therefore, we consider the moving bodies, we must unquestionably regard
the motion of the earth as a much simpler process than that of the universe;
if, furthermore, we direct our attention to so many other simplifications
which may be reached only by this theory, the daily movement of the earth
must appear much more probable than the motion of the universe without
the earth, for, according to Aristotle's just axiom, 'Frustra fit per plura, quod
potest fieri per p auciora' (It is vain to expend many means where a few are
sufficient)."(2)
The work was widely circulated, and it was received with an interest
which bespeaks a wide-spread undercurrent of belief in the Copernican
doctrine. Naturally enough, it attracted immediate attention from the church
authorities. Galileo was summoned to appear at Rome to defend his
conduct. The philosopher, who was now in his seventieth year, pleaded age
and infirmity. He had no desire for personal experience of the tribunal of the
Inquisition; but the mandate was repeated, and Galileo went to Rome.
There, as every one knows, he disavowed any intention to oppose the
teachings of Scripture, and formally renounced the heretical doctrine of the
earth's motion. According to a tale which so long passed current that every
historian must still repeat it though no one now believes it authentic,
Galileo qualified his renunciation by muttering to himself, "E pur si muove"
(It does move, none the less), as he rose to his feet and retired from the
presence of his persecutors. The tale is one of those fictions which the
dramatic sense of humanity is wont to impose upon history, but, like most
such fictions, it expresses the spirit if not the letter of truth; for just as no
one believes that Galileo's lips uttered the phrase, so no one doubts that the
rebellious words were in his mind.
After his formal renunciation, Galileo was allowed to depart, but with the
injunction that he abstain in future from heretical teaching. The remaining
ten years of his life were devoted chiefly to mechanics, where his
experiments fortunately opposed the Aristotelian rather than the Hebrew
teachings. Galileo's death occurred in 1642, a hundred years after the death
of Copernicus. Kepler had died thirteen years before, and there remained no
astronomer in the field who is conspicuous in the history of science as a
champion of the Copernican doctrine. But in truth it might be said that the
theory no longer needed a champion. The researches of Kepler and Galileo
had produced a mass of evidence for the Copernican theory which

amounted to demonstration. A generation or two might be required for this
evidence to make itself everywhere known among men of science, and of
course the ecclesiastical authorities must be expected to stand by their guns
for a somewhat longer period. In point of fact, the ecclesiastical ban was not
technically removed by the striking of the Copernican books from the list of
the Index Expurgatorius until the year 1822, almost two hundred years after
the date of Galileo's dialogue. But this, of course, is in no sense a guide to
the state of general opinion regarding the theory. We shall gain a true gauge
as to this if we assume that the greater number of important thinkers had
accepted the heliocentric doctrine before the middle of the seventeenth
century, and that before the close of that century the old Ptolemaic idea had
been quite abandoned. A wonderful revolution in man's estimate of the
universe had thus been effected within about two centuries after the birth of
Copernicus.

V. GALILEO AND THE NEW PHYSICS
After Galileo had felt the strong hand of the Inquisition, in 1632, he was
careful to confine his researches, or at least his publications, to topics that
seemed free from theological implications. In doing so he reverted to the
field of his earliest studies—namely, the field of mechanics; and the
Dialoghi delle Nuove Scienze, which he finished in 1636, and which was
printed two years later, attained a celebrity no less than that of the heretical
dialogue that had preceded it. The later work was free from all apparent
heresies, yet perhaps it did more towards the establishment of the
Copernican doctrine, through the teaching of correct mechanical principles,
than the other work had accomplished by a more direct method.
Galileo's astronomical discoveries were, as we have seen, in a sense
accidental; at least, they received their inception through the inventive
genius of another. His mechanical discoveries, on the other hand, were the
natural output of his own creative genius. At the very beginning of his
career, while yet a very young man, though a professor of mathematics at
Pisa, he had begun that onslaught upon the old Aristotelian ideas which he
was to continue throughout his life. At the famous leaning tower in Pisa, the
young iconoclast performed, in the year 1590, one of the most theatrical
demonstrations in the history of science. Assembling a multitude of
champions of the old ideas, he proposed to demonstrate the falsity of the
Aristotelian doctrine that the velocity of falling bodies is proportionate to
their weight. There is perhaps no fact more strongly illustrative of the
temper of the Middle Ages than the fact that this doctrine, as taught by the
Aristotelian philosopher, should so long have gone unchallenged. Now,
however, it was put to the test; Galileo released a half-pound weight and a
hundred-pound cannon-ball from near the top of the tower, and, needless to
say, they reached the ground together. Of course, the spectators were but
little pleased with what they saw. They could not doubt the evidence of their
own senses as to the particular experiment in question; they could suggest,
however, that the experiment involved a violation of the laws of nature
through the practice of magic. To controvert so firmly established an idea
savored of heresy. The young man guilty of such iconoclasm was naturally

looked at askance by the scholarship of his time. Instead of being
applauded, he was hissed, and he found it expedient presently to retire from
Pisa.
Fortunately, however, the new spirit of progress had made itself felt more
effectively in some other portions of Italy, and so Galileo found a refuge
and a following in Padua, and afterwards in Florence; and while, as we have
seen, he was obliged to curb his enthusiasm regarding the subject that was
perhaps nearest his heart—the promulgation of the Copernican theory—yet
he was permitted in the main to carry on his experimental observations
unrestrained. These experiments gave him a place of unquestioned authority
among his contemporaries, and they have transmitted his name to posterity
as that of one of the greatest of experimenters and the virtual founder of
modern mechanical science. The experiments in question range over a wide
field; but for the most part they have to do with moving bodies and with
questions of force, or, as we should now say, of energy. The experiment at
the leaning tower showed that the velocity of falling bodies is independent
of the weight of the bodies, provided the weight is sufficient to overcome
the resistance of the atmosphere. Later experiments with falling bodies led
to the discovery of laws regarding the accelerated velocity of fall. Such
velocities were found to bear a simple relation to the period of time from
the beginning of the fall. Other experiments, in which balls were allowed to
roll down inclined planes, corroborated the observation that the pull of
gravitation gave a velocity proportionate to the length of fall, whether such
fall were direct or in a slanting direction.
These studies were associated with observations on projectiles, regarding
which Galileo was the first to entertain correct notions. According to the
current idea, a projectile fired, for example, from a cannon, moved in a
straight horizontal line until the propulsive force was exhausted, and then
fell to the ground in a perpendicular line. Galileo taught that the projectile
begins to fall at once on leaving the mouth of the cannon and traverses a
parabolic course. According to his idea, which is now familiar to every one,
a cannon-ball dropped from the level of the cannon's muzzle will strike the
ground simultaneously with a ball fired horizontally from the cannon. As to
the paraboloid course pursued by the projectile, the resistance of the air is a
factor which Galileo could not accurately compute, and which interferes
with the practical realization of his theory. But this is a minor consideration.
The great importance of his idea consists in the recognition that such a force

as that of gravitation acts in precisely the same way upon all unsupported
bodies, whether or not such bodies be at the same time acted upon by a
force of translation.
Out of these studies of moving bodies was gradually developed a correct
notion of several important general laws of mechanics—laws a knowledge
of which was absolutely essential to the progress of physical science. The
belief in the rotation of the earth made necessary a clear conception that all
bodies at the surface of the earth partake of that motion quite independently
of their various observed motions in relation to one another. This idea was
hard to grasp, as an oft-repeated argument shows. It was asserted again and
again that, if the earth rotates, a stone dropped from the top of a tower could
not fall at the foot of the tower, since the earth's motion would sweep the
tower far away from its original position while the stone is in transit.
This was one of the stock arguments against the earth's motion, yet it was
one that could be refuted with the greatest ease by reasoning from strictly
analogous experiments. It might readily be observed, for example, that a
stone dropped from a moving cart does not strike the ground directly below
the point from which it is dropped, but partakes of the forward motion of
the cart. If any one doubt this he has but to jump from a moving cart to be
given a practical demonstration of the fact that his entire body was in some
way influenced by the motion of translation. Similarly, the simple
experiment of tossing a ball from the deck of a moving ship will convince
any one that the ball partakes of the motion of the ship, so that it can be
manipulated precisely as if the manipulator were standing on the earth. In
short, every-day experience gives us illustrations of what might be called
compound motion, which makes it seem altogether plausible that, if the
earth is in motion, objects at its surface will partake of that motion in a way
that does not interfere with any other movements to which they may be
subjected. As the Copernican doctrine made its way, this idea of compound
motion naturally received more and more attention, and such experiments
as those of Galileo prepared the way for a new interpretation of the
mechanical principles involved.
The great difficulty was that the subject of moving bodies had all along
been contemplated from a wrong point of view. Since force must be applied
to an object to put it in motion, it was perhaps not unnaturally assumed that
similar force must continue to be applied to keep the object in motion.

When, for example, a stone is thrown from the hand, the direct force
applied necessarily ceases as soon as the projectile leaves the hand. The
stone, nevertheless, flies on for a certain distance and then falls to the
ground. How is this flight of the stone to be explained? The ancient
philosophers puzzled more than a little over this problem, and the
Aristotelians reached the conclusion that the motion of the hand had
imparted a propulsive motion to the air, and that this propulsive motion was
transmitted to the stone, pushing it on. Just how the air took on this
propulsive property was not explained, and the vagueness of thought that
characterized the time did not demand an explanation. Possibly the dying
away of ripples in water may have furnished, by analogy, an explanation of
the gradual dying out of the impulse which propels the stone.
All of this was, of course, an unfortunate maladjustment of the point of
view. As every one nowadays knows, the air retards the progress of the
stone, enabling the pull of gravitation to drag it to the earth earlier than it
otherwise could. Were the resistance of the air and the pull of gravitation
removed, the stone as projected from the hand would fly on in a straight
line, at an unchanged velocity, forever. But this fact, which is expressed in
what we now term the first law of motion, was extremely difficult to grasp.
The first important step towards it was perhaps implied in Galileo's study of
falling bodies. These studies, as we have seen, demonstrated that a half-
pound weight and a hundred-pound weight fall with the same velocity. It is,
however, matter of common experience that certain bodies, as, for example,
feathers, do not fall at the same rate of speed with these heavier bodies. This
anomaly demands an explanation, and the explanation is found in the
resistance offered the relatively light object by the air. Once the idea that the
air may thus act as an impeding force was grasped, the investigator of
mechanical principles had entered on a new and promising course.
Galileo could not demonstrate the retarding influence of air in the way
which became familiar a generation or two later; he could not put a feather
and a coin in a vacuum tube and prove that the two would there fall with
equal velocity, because, in his day, the air-pump had not yet been invented.
The experiment was made only a generation after the time of Galileo, as we
shall see; but, meantime, the great Italian had fully grasped the idea that
atmospheric resistance plays a most important part in regard to the motion
of falling and projected bodies. Thanks largely to his own experiments, but
partly also to the efforts of others, he had come, before the end of his life,

pretty definitely to realize that the motion of a projectile, for example, must
be thought of as inherent in the projectile itself, and that the retardation or
ultimate cessation of that motion is due to the action of antagonistic forces.
In other words, he had come to grasp the meaning of the first law of motion.
It remained, however, for the great Frenchman Descartes to give precise
expression to this law two years after Galileo's death. As Descartes
expressed it in his Principia Philosophiae, published in 1644, any body once
in motion tends to go on in a straight line, at a uniform rate of speed,
forever. Contrariwise, a stationary body will remain forever at rest unless
acted on by some disturbing force.
This all-important law, which lies at the very foundation of all true
conceptions of mechanics, was thus worked out during the first half of the
seventeenth century, as the outcome of numberless experiments for which
Galileo's experiments with failing bodies furnished the foundation. So
numerous and so gradual were the steps by which the reversal of view
regarding moving bodies was effected that it is impossible to trace them in
detail. We must be content to reflect that at the beginning of the Galilean
epoch utterly false notions regarding the subject were entertained by the
very greatest philosophers—by Galileo himself, for example, and by Kepler
—whereas at the close of that epoch the correct and highly illuminative
view had been attained.
We must now consider some other experiments of Galileo which led to
scarcely less-important results. The experiments in question had to do with
the movements of bodies passing down an inclined plane, and with the
allied subject of the motion of a pendulum. The elaborate experiments of
Galileo regarding the former subject were made by measuring the velocity
of a ball rolling down a plane inclined at various angles. He found that the
velocity acquired by a ball was proportional to the height from which the
ball descended regardless of the steepness of the incline. Experiments were
made also with a ball rolling down a curved gutter, the curve representing
the are of a circle. These experiments led to the study of the curvilinear
motions of a weight suspended by a cord; in other words, of the pendulum.
Regarding the motion of the pendulum, some very curious facts were
soon ascertained. Galileo found, for example, that a pendulum of a given
length performs its oscillations with the same frequency though the arc
described by the pendulum be varied greatly.(1) He found, also, that the rate

of oscillation for pendulums of different lengths varies according to a
simple law. In order that one pendulum shall oscillate one-half as fast as
another, the length of the pendulums must be as four to one. Similarly, by
lengthening the pendulums nine times, the oscillation is reduced to one-
third, In other words, the rate of oscillation of pendulums varies inversely
as the square of their length. Here, then, is a simple relation between the
motions of swinging bodies which suggests the relation which Kepler bad
discovered between the relative motions of the planets. Every such
discovery coming in this age of the rejuvenation of experimental science
had a peculiar force in teaching men the all-important lesson that simple
laws lie back of most of the diverse phenomena of nature, if only these laws
can be discovered.
Galileo further observed that his pendulum might be constructed of any
weight sufficiently heavy readily to overcome the atmospheric resistance,
and that, with this qualification, neither the weight nor the material had any
influence upon the time of oscillation, this being solely determined by the
length of the cord. Naturally, the practical utility of these discoveries was
not overlooked by Galileo. Since a pendulum of a given length oscillates
with unvarying rapidity, here is an obvious means of measuring time.
Galileo, however, appears not to have met with any great measure of
success in putting this idea into practice. It remained for the mechanical
ingenuity of Huyghens to construct a satisfactory pendulum clock.
As a theoretical result of the studies of rolling and oscillating bodies,
there was developed what is usually spoken of as the third law of motion—
namely, the law that a given force operates upon a moving body with an
effect proportionate to its effect upon the same body when at rest. Or, as
Whewell states the law: "The dynamical effect of force is as the statical
effect; that is, the velocity which any force generates in a given time, when
it puts the body in motion, is proportional to the pressure which this same
force produces in a body at rest."(2) According to the second law of motion,
each one of the different forces, operating at the same time upon a moving
body, produces the same effect as if it operated upon the body while at rest.
STEVINUS AND THE LAW OF EQUILIBRIUM
It appears, then, that the mechanical studies of Galileo, taken as a whole,
were nothing less than revolutionary. They constituted the first great
advance upon the dynamic studies of Archimedes, and then led to the secure

foundation for one of the most important of modern sciences. We shall see
that an important company of students entered the field immediately after
the time of Galileo, and carried forward the work he had so well begun. But
before passing on to the consideration of their labors, we must consider
work in allied fields of two men who were contemporaries of Galileo and
whose original labors were in some respects scarcely less important than his
own. These men are the Dutchman Stevinus, who must always be
remembered as a co-laborer with Galileo in the foundation of the science of
dynamics, and the Englishman Gilbert, to whom is due the unqualified
praise of first subjecting the phenomenon of magnetism to a strictly
scientific investigation.
Stevinus was born in the year 1548, and died in 1620. He was a man of a
practical genius, and he attracted the attention of his non-scientific
contemporaries, among other ways, by the construction of a curious land-
craft, which, mounted on wheels, was to be propelled by sails like a boat.
Not only did he write a book on this curious horseless carriage, but he put
his idea into practical application, producing a vehicle which actually
traversed the distance between Scheveningen and Petton, with no fewer
than twenty-seven passengers, one of them being Prince Maurice of
Orange. This demonstration was made about the year 1600. It does not
appear, however, that any important use was made of the strange vehicle;
but the man who invented it put his mechanical ingenuity to other use with
better effect. It was he who solved the problem of oblique forces, and who
discovered the important hydrostatic principle that the pressure of fluids is
proportionate to their depth, without regard to the shape of the including
vessel.
The study of oblique forces was made by Stevinus with the aid of
inclined planes. His most demonstrative experiment was a very simple one,
in which a chain of balls of equal weight was hung from a triangle; the
triangle being so constructed as to rest on a horizontal base, the oblique
sides bearing the relation to each other of two to one. Stevinus found that
his chain of balls just balanced when four balls were on the longer side and
two on the shorter and steeper side. The balancing of force thus brought
about constituted a stable equilibrium, Stevinus being the first to
discriminate between such a condition and the unbalanced condition called
unstable equilibrium. By this simple experiment was laid the foundation of
the science of statics. Stevinus had a full grasp of the principle which his

experiment involved, and he applied it to the solution of oblique forces in
all directions. Earlier investigations of Stevinus were published in 1608. His
collected works were published at Leyden in 1634.
This study of the equilibrium of pressure of bodies at rest led Stevinus,
not unnaturally, to consider the allied subject of the pressure of liquids. He
is to be credited with the explanation of the so-called hydrostatic paradox.
The familiar modern experiment which illustrates this paradox is made by
inserting a long perpendicular tube of small caliber into the top of a tight
barrel. On filling the barrel and tube with water, it is possible to produce a
pressure which will burst the barrel, though it be a strong one, and though
the actual weight of water in the tube is comparatively insignificant. This
illustrates the fact that the pressure at the bottom of a column of liquid is
proportionate to the height of the column, and not to its bulk, this being the
hydrostatic paradox in question. The explanation is that an enclosed fluid
under pressure exerts an equal force upon all parts of the circumscribing
wall; the aggregate pressure may, therefore, be increased indefinitely by
increasing the surface. It is this principle, of course, which is utilized in the
familiar hydrostatic press. Theoretical explanations of the pressure of
liquids were supplied a generation or two later by numerous investigators,
including Newton, but the practical refoundation of the science of
hydrostatics in modern times dates from the experiments of Stevinus.
GALILEO AND THE EQUILIBRIUM OF FLUIDS
Experiments of an allied character, having to do with the equilibrium of
fluids, exercised the ingenuity of Galileo. Some of his most interesting
experiments have to do with the subject of floating bodies. It will be
recalled that Archimedes, away back in the Alexandrian epoch, had solved
the most important problems of hydrostatic equilibrium. Now, however, his
experiments were overlooked or forgotten, and Galileo was obliged to make
experiments anew, and to combat fallacious views that ought long since to
have been abandoned. Perhaps the most illuminative view of the spirit of
the times can be gained by quoting at length a paper of Galileo's, in which
he details his own experiments with floating bodies and controverts the
views of his opponents. The paper has further value as illustrating Galileo's
methods both as experimenter and as speculative reasoner.
The current view, which Galileo here undertakes to refute, asserts that
water offers resistance to penetration, and that this resistance is instrumental

in determining whether a body placed in water will float or sink. Galileo
contends that water is non-resistant, and that bodies float or sink in virtue of
their respective weights. This, of course, is merely a restatement of the law
of Archimedes. But it remains to explain the fact that bodies of a certain
shape will float, while bodies of the same material and weight, but of a
different shape, will sink. We shall see what explanation Galileo finds of
this anomaly as we proceed.
In the first place, Galileo makes a cone of wood or of wax, and shows
that when it floats with either its point or its base in the water, it displaces
exactly the same amount of fluid, although the apex is by its shape better
adapted to overcome the resistance of the water, if that were the cause of
buoyancy. Again, the experiment may be varied by tempering the wax with
filings of lead till it sinks in the water, when it will be found that in any
figure the same quantity of cork must be added to it to raise the surface.
"But," says Galileo, "this silences not my antagonists; they say that all
the discourse hitherto made by me imports little to them, and that it serves
their turn; that they have demonstrated in one instance, and in such manner
and figure as pleases them best—namely, in a board and in a ball of ebony
—that one when put into the water sinks to the bottom, and that the other
stays to swim on the top; and the matter being the same, and the two bodies
differing in nothing but in figure, they affirm that with all perspicuity they
have demonstrated and sensibly manifested what they undertook.
Nevertheless, I believe, and think I can prove, that this very experiment
proves nothing against my theory. And first, it is false that the ball sinks and
the board not; for the board will sink, too, if you do to both the figures as
the words of our question require; that is, if you put them both in the water;
for to be in the water implies to be placed in the water, and by Aristotle's
own definition of place, to be placed imports to be environed by the surface
of the ambient body; but when my antagonists show the floating board of
ebony, they put it not into the water, but upon the water; where, being
detained by a certain impediment (of which more anon), it is surrounded,
partly with water, partly with air, which is contrary to our agreement, for
that was that bodies should be in the water, and not part in the water, part in
the air.
"I will not omit another reason, founded also upon experience, and, if I
deceive not myself, conclusive against the notion that figure, and the

resistance of the water to penetration, have anything to do with the
buoyancy of bodies. Choose a piece of wood or other matter, as, for
instance, walnut-wood, of which a ball rises from the bottom of the water to
the surface more slowly than a ball of ebony of the same size sinks, so that,
clearly, the ball of ebony divides the water more readily in sinking than the
ball of wood does in rising. Then take a board of walnut-tree equal to and
like the floating one of my antagonists; and if it be true that this latter floats
by reason of the figure being unable to penetrate the water, the other of
walnut-tree, without a question, if thrust to the bottom, ought to stay there,
as having the same impeding figure, and being less apt to overcome the said
resistance of the water. But if we find by experience that not only the thin
board, but every other figure of the same walnut-tree, will return to float, as
unquestionably we shall, then I must desire my opponents to forbear to
attribute the floating of the ebony to the figure of the board, since the
resistance of the water is the same in rising as in sinking, and the force of
ascension of the walnut-tree is less than the ebony's force for going to the
bottom.
"Now let us return to the thin plate of gold or silver, or the thin board of
ebony, and let us lay it lightly upon the water, so that it may stay there
without sinking, and carefully observe the effect. It will appear clearly that
the plates are a considerable matter lower than the surface of the water,
which rises up and makes a kind of rampart round them on every side. But
if it has already penetrated and overcome the continuity of the water, and is
of its own nature heavier than the water, why does it not continue to sink,
but stop and suspend itself in that little dimple that its weight has made in
the water? My answer is, because in sinking till its surface is below the
water, which rises up in a bank round it, it draws after and carries along
with it the air above it, so that that which, in this case, descends in the water
is not only the board of ebony or the plate of iron, but a compound of ebony
and air, from which composition results a solid no longer specifically
heavier than the water, as was the ebony or gold alone. But, gentlemen, we
want the same matter; you are to alter nothing but the shape, and, therefore,
have the goodness to remove this air, which may be done simply by
washing the surface of the board, for the water having once got between the
board and the air will run together, and the ebony will go to the bottom; and
if it does not, you have won the day.

"But methinks I hear some of my antagonists cunningly opposing this,
and telling me that they will not on any account allow their boards to be
wetted, because the weight of the water so added, by making it heavier than
it was before, draws it to the bottom, and that the addition of new weight is
contrary to our agreement, which was that the matter should be the same.
"To this I answer, first, that nobody can suppose bodies to be put into the
water without their being wet, nor do I wish to do more to the board than
you may do to the ball. Moreover, it is not true that the board sinks on
account of the weight of the water added in the washing; for I will put ten
or twenty drops on the floating board, and so long as they stand separate it
shall not sink; but if the board be taken out and all that water wiped off, and
the whole surface bathed with one single drop, and put it again upon the
water, there is no question but it will sink, the other water running to cover
it, being no longer hindered by the air. In the next place, it is altogether
false that water can in any way increase the weight of bodies immersed in
it, for water has no weight in water, since it does not sink. Now just as he
who should say that brass by its own nature sinks, but that when formed
into the shape of a kettle it acquires from that figure the virtue of lying in
water without sinking, would say what is false, because that is not purely
brass which then is put into the water, but a compound of brass and air; so
is it neither more nor less false that a thin plate of brass or ebony swims by
virtue of its dilated and broad figure. Also, I cannot omit to tell my
opponents that this conceit of refusing to bathe the surface of the board
might beget an opinion in a third person of a poverty of argument on their
side, especially as the conversation began about flakes of ice, in which it
would be simple to require that the surfaces should be kept dry; not to
mention that such pieces of ice, whether wet or dry, always float, and so my
antagonists say, because of their shape.
"Some may wonder that I affirm this power to be in the air of keeping
plate of brass or silver above water, as if in a certain sense I would attribute
to the air a kind of magnetic virtue for sustaining heavy bodies with which
it is in contact. To satisfy all these doubts I have contrived the following
experiment to demonstrate how truly the air does support these bodies; for I
have found, when one of these bodies which floats when placed lightly on
the water is thoroughly bathed and sunk to the bottom, that by carrying
down to it a little air without otherwise touching it in the least, I am able to
raise and carry it back to the top, where it floats as before. To this effect, I

take a ball of wax, and with a little lead make it just heavy enough to sink
very slowly to the bottom, taking care that its surface be quite smooth and
even. This, if put gently into the water, submerges almost entirely, there
remaining visible only a little of the very top, which, so long as it is joined
to the air, keeps the ball afloat; but if we take away the contact of the air by
wetting this top, the ball sinks to the bottom and remains there. Now to
make it return to the surface by virtue of the air which before sustained it,
thrust into the water a glass with the mouth downward, which will carry
with it the air it contains, and move this down towards the ball until you
see, by the transparency of the glass, that the air has reached the top of it;
then gently draw the glass upward, and you will see the ball rise, and
afterwards stay on the top of the water, if you carefully part the glass and
water without too much disturbing it."(3)
It will be seen that Galileo, while holding in the main to a correct thesis,
yet mingles with it some false ideas. At the very outset, of course, it is not
true that water has no resistance to penetration; it is true, however, in the
sense in which Galileo uses the term—that is to say, the resistance of the
water to penetration is not the determining factor ordinarily in deciding
whether a body sinks or floats. Yet in the case of the flat body it is not
altogether inappropriate to say that the water resists penetration and thus
supports the body. The modern physicist explains the phenomenon as due to
surface-tension of the fluid. Of course, Galileo's disquisition on the mixing
of air with the floating body is utterly fanciful. His experiments were
beautifully exact; his theorizing from them was, in this instance, altogether
fallacious. Thus, as already intimated, his paper is admirably adapted to
convey a double lesson to the student of science.
WILLIAM GILBERT AND THE STUDY OF MAGNETISM
It will be observed that the studies of Galileo and Stevinus were chiefly
concerned with the force of gravitation. Meanwhile, there was an English
philosopher of corresponding genius, whose attention was directed towards
investigation of the equally mysterious force of terrestrial magnetism. With
the doubtful exception of Bacon, Gilbert was the most distinguished man of
science in England during the reign of Queen Elizabeth. He was for many
years court physician, and Queen Elizabeth ultimately settled upon him a
pension that enabled him to continue his researches in pure science.

His investigations in chemistry, although supposed to be of great
importance, are mostly lost; but his great work, De Magnete, on which he
labored for upwards of eighteen years, is a work of sufficient importance, as
Hallam says, "to raise a lasting reputation for its author." From its first
appearance it created a profound impression upon the learned men of the
continent, although in England Gilbert's theories seem to have been
somewhat less favorably received. Galileo freely expressed his admiration
for the work and its author; Bacon, who admired the author, did not express
the same admiration for his theories; but Dr. Priestley, later, declared him to
be "the father of modern electricity."
Strangely enough, Gilbert's book had never been translated into English,
or apparently into any other language, until recent years, although at the
time of its publication certain learned men, unable to read the book in the
original, had asked that it should be. By this neglect, or oversight, a great
number of general readers as well as many scientists, through succeeding
centuries, have been deprived of the benefit of writings that contained a
good share of the fundamental facts about magnetism as known to-day.
Gilbert was the first to discover that the earth is a great magnet, and he
not only gave the name of "pole" to the extremities of the magnetic needle,
but also spoke of these "poles" as north and south pole, although he used
these names in the opposite sense from that in which we now use them, his
south pole being the extremity which pointed towards the north, and vice
versa. He was also first to make use of the terms "electric force," "electric
emanations," and "electric attractions."
It is hardly necessary to say that some of the views taken by Gilbert,
many of his theories, and the accuracy of some of his experiments have in
recent times been found to be erroneous. As a pioneer in an unexplored
field of science, however, his work is remarkably accurate. "On the whole,"
says Dr. John Robinson, "this performance contains more real information
than any writing of the age in which he lived, and is scarcely exceeded by
any that has appeared since."(4)
In the preface to his work Gilbert says: "Since in the discovery of secret
things, and in the investigation of hidden causes, stronger reasons are
obtained from sure experiments and demonstrated arguments than from
probable conjectures and the opinions of philosophical speculators of the
common sort, therefore, to the end of that noble substance of that great

loadstone, our common mother (the earth), still quite unknown, and also
that the forces extraordinary and exalted of this globe may the better be
understood, we have decided, first, to begin with the common stony and
ferruginous matter, and magnetic bodies, and the part of the earth that we
may handle and may perceive with senses, and then to proceed with plain
magnetic experiments, and to penetrate to the inner parts of the earth."(5)
Before taking up the demonstration that the earth is simply a giant
loadstone, Gilbert demonstrated in an ingenious way that every loadstone,
of whatever size, has definite and fixed poles. He did this by placing the
stone in a metal lathe and converting it into a sphere, and upon this sphere
demonstrated how the poles can be found. To this round loadstone he gave
the name of terrella—that is, little earth.
"To find, then, poles answering to the earth," he says, "take in your hand
the round stone, and lay on it a needle or a piece of iron wire: the ends of
the wire move round their middle point, and suddenly come to a standstill.
Now, with ochre or with chalk, mark where the wire lies still and sticks.
Then move the middle or centre of the wire to another spot, and so to a third
and fourth, always marking the stone along the length of the wire where it
stands still; the lines so marked will exhibit meridian circles, or circles like
meridians, on the stone or terrella; and manifestly they will all come
together at the poles of the stone. The circle being continued in this way, the
poles appear, both the north and the south, and betwixt these, midway, we
may draw a large circle for an equator, as is done by the astronomer in the
heavens and on his spheres, and by the geographer on the terrestrial globe."
(6)
Gilbert had tried the familiar experiment of placing the loadstone on a
float in water, and observed that the poles always revolved until they
pointed north and south, which he explained as due to the earth's magnetic
attraction. In this same connection he noticed that a piece of wrought iron
mounted on a cork float was attracted by other metals to a slight degree, and
he observed also that an ordinary iron bar, if suspended horizontally by a
thread, assumes invariably a north and south direction. These, with many
other experiments of a similar nature, convinced him that the earth "is a
magnet and a loadstone," which he says is a "new and till now unheard-of
view of the earth."

Fully to appreciate Gilbert's revolutionary views concerning the earth as
a magnet, it should be remembered that numberless theories to explain the
action of the electric needle had been advanced. Columbus and Paracelsus,
for example, believed that the magnet was attracted by some point in the
heavens, such as a magnetic star. Gilbert himself tells of some of the beliefs
that had been held by his predecessors, many of whom he declares "wilfully
falsify." One of his first steps was to refute by experiment such assertions as
that of Cardan, that "a wound by a magnetized needle was painless"; and
also the assertion of Fracastoni that loadstone attracts silver; or that of
Scalinger, that the diamond will attract iron; and the statement of
Matthiolus that "iron rubbed with garlic is no longer attracted to the
loadstone."
Gilbert made extensive experiments to explain the dipping of the needle,
which had been first noticed by William Norman. His deduction as to this
phenomenon led him to believe that this was also explained by the magnetic
attraction of the earth, and to predict where the vertical dip would be found.
These deductions seem the more wonderful because at the time he made
them the dip had just been discovered, and had not been studied except at
London. His theory of the dip was, therefore, a scientific prediction, based
on a preconceived hypothesis. Gilbert found the dip to be 72 degrees at
London; eight years later Hudson found the dip at 75 degrees 22' north
latitude to be 89 degrees 30'; but it was not until over two hundred years
later, in 1831, that the vertical dip was first observed by Sir James Ross at
about 70 degrees 5' north latitude, and 96 degrees 43' west longitude. This
was not the exact point assumed by Gilbert, and his scientific predictions,
therefore, were not quite correct; but such comparatively slight and
excusable errors mar but little the excellence of his work as a whole.
A brief epitome of some of his other important discoveries suffices to
show that the exalted position in science accorded him by contemporaries,
as well as succeeding generations of scientists, was well merited. He was
first to distinguish between magnetism and electricity, giving the latter its
name. He discovered also the "electrical charge," and pointed the way to the
discovery of insulation by showing that the charge could be retained some
time in the excited body by covering it with some non-conducting
substance, such as silk; although, of course, electrical conduction can hardly
be said to have been more than vaguely surmised, if understood at all by
him. The first electrical instrument ever made, and known as such, was

invented by him, as was also the first magnetometer, and the first electrical
indicating device. Although three centuries have elapsed since his death, the
method of magnetizing iron first introduced by him is in common use to-
day.
He made exhaustive experiments with a needle balanced on a pivot to see
how many substances he could find which, like amber, on being rubbed
affected the needle. In this way he discovered that light substances were
attracted by alum, mica, arsenic, sealing-wax, lac sulphur, slags, beryl,
amethyst, rock-crystal, sapphire, jet, carbuncle, diamond, opal, Bristol
stone, glass, glass of antimony, gum-mastic, hard resin, rock-salt, and, of
course, amber. He discovered also that atmospheric conditions affected the
production of electricity, dryness being unfavorable and moisture favorable.
Galileo's estimate of this first electrician is the verdict of succeeding
generations. "I extremely admire and envy this author," he said. "I think
him worthy of the greatest praise for the many new and true observations
which he has made, to the disgrace of so many vain and fabling authors."
STUDIES OF LIGHT, HEAT, AND ATMOSPHERIC PRESSURE
We have seen that Gilbert was by no means lacking in versatility, yet the
investigations upon which his fame is founded were all pursued along one
line, so that the father of magnetism may be considered one of the earliest
of specialists in physical science. Most workers of the time, on the other
band, extended their investigations in many directions. The sum total of
scientific knowledge of that day had not bulked so large as to exclude the
possibility that one man might master it all. So we find a Galileo, for
example, making revolutionary discoveries in astronomy, and performing
fundamental experiments in various fields of physics. Galileo's great
contemporary, Kepler, was almost equally versatile, though his
astronomical studies were of such pre-eminent importance that his other
investigations sink into relative insignificance. Yet he performed some
notable experiments in at least one department of physics. These
experiments had to do with the refraction of light, a subject which Kepler
was led to investigate, in part at least, through his interest in the telescope.
We have seen that Ptolemy in the Alexandrian time, and Alhazen, the
Arab, made studies of refraction. Kepler repeated their experiments, and,
striving as always to generalize his observations, he attempted to find the
law that governed the observed change of direction which a ray of light

assumes in passing from one medium to another. Kepler measured the angle
of refraction by means of a simple yet ingenious trough-like apparatus
which enabled him to compare readily the direct and refracted rays. He
discovered that when a ray of light passes through a glass plate, if it strikes
the farther surface of the glass at an angle greater than 45 degrees it will be
totally refracted instead of passing through into the air. He could not well
fail to know that different mediums refract light differently, and that for the
same medium the amount of light valies with the change in the angle of
incidence. He was not able, however, to generalize his observations as he
desired, and to the last the law that governs refraction escaped him. It
remained for Willebrord Snell, a Dutchman, about the year 1621, to
discover the law in question, and for Descartes, a little later, to formulate it.
Descartes, indeed, has sometimes been supposed to be the discoverer of the
law. There is reason to believe that he based his generalizations on the
experiment of Snell, though he did not openly acknowledge his
indebtedness. The law, as Descartes expressed it, states that the sine of the
angle of incidence bears a fixed ratio to the sine of the angle of refraction
for any given medium. Here, then, was another illustration of the fact that
almost infinitely varied phenomena may be brought within the scope of a
simple law. Once the law had been expressed, it could be tested and verified
with the greatest ease; and, as usual, the discovery being made, it seems
surprising that earlier investigators—in particular so sagacious a guesser as
Kepler—should have missed it.
Galileo himself must have been to some extent a student of light, since,
as we have seen, he made such notable contributions to practical optics
through perfecting the telescope; but he seems not to have added anything
to the theory of light. The subject of heat, however, attracted his attention in
a somewhat different way, and he was led to the invention of the first
contrivance for measuring temperatures. His thermometer was based on the
afterwards familiar principle of the expansion of a liquid under the
influence of heat; but as a practical means of measuring temperature it was
a very crude affair, because the tube that contained the measuring liquid
was exposed to the air, hence barometric changes of pressure vitiated the
experiment. It remained for Galileo's Italian successors of the Accademia
del Cimento of Florence to improve upon the apparatus, after the
experiments of Torricelli—to which we shall refer in a moment—had
thrown new light on the question of atmospheric pressure. Still later the

celebrated Huygens hit upon the idea of using the melting and the boiling
point of water as fixed points in a scale of measurements, which first gave
definiteness to thermometric tests.
TORRICELLI
In the closing years of his life Galileo took into his family, as his adopted
disciple in science, a young man, Evangelista Torricelli (1608-1647), who
proved himself, during his short lifetime, to be a worthy follower of his
great master. Not only worthy on account of his great scientific discoveries,
but grateful as well, for when he had made the great discovery that the
"suction" made by a vacuum was really nothing but air pressure, and not
suction at all, he regretted that so important a step in science might not have
been made by his great teacher, Galileo, instead of by himself. "This
generosity of Torricelli," says Playfair, "was, perhaps, rarer than his genius:
there are more who might have discovered the suspension of mercury in the
barometer than who would have been willing to part with the honor of the
discovery to a master or a friend."
Torricelli's discovery was made in 1643, less than two years after the
death of his master. Galileo had observed that water will not rise in an
exhausted tube, such as a pump, to a height greater than thirty-three feet,
but he was never able to offer a satisfactory explanation of the principle.
Torricelli was able to demonstrate that the height at which the water stood
depended upon nothing but its weight as compared with the weight of air. If
this be true, it is evident that any fluid will be supported at a definite height,
according to its relative weight as compared with air. Thus mercury, which
is about thirteen times more dense than water, should only rise to one-
thirteenth the height of a column of water—that is, about thirty inches.
Reasoning in this way, Torricelli proceeded to prove that his theory was
correct. Filling a long tube, closed at one end, with mercury, he inverted the
tube with its open orifice in a vessel of mercury. The column of mercury
fell at once, but at a height of about thirty inches it stopped and remained
stationary, the pressure of the air on the mercury in the vessel maintaining it
at that height. This discovery was a shattering blow to the old theory that
had dominated that field of physics for so many centuries. It was
completely revolutionary to prove that, instead of a mysterious something
within the tube being responsible for the suspension of liquids at certain
heights, it was simply the ordinary atmospheric pressure mysterious

enough, it is true—pushing upon them from without. The pressure exerted
by the atmosphere was but little understood at that time, but Torricelli's
discovery aided materially in solving the mystery. The whole class of
similar phenomena of air pressure, which had been held in the trammel of
long-established but false doctrines, was now reduced to one simple law,
and the door to a solution of a host of unsolved problems thrown open.
It had long been suspected and believed that the density of the
atmosphere varies at certain times. That the air is sometimes "heavy" and at
other times "light" is apparent to the senses without scientific apparatus for
demonstration. It is evident, then, that Torricelli's column of mercury should
rise and fall just in proportion to the lightness or heaviness of the air. A
short series of observations proved that it did so, and with those
observations went naturally the observations as to changes in the weather. It
was only necessary, therefore, to scratch a scale on the glass tube, indicating
relative atmospheric pressures, and the Torricellian barometer was
complete.
Such a revolutionary theory and such an important discovery were, of
course, not to be accepted without controversy, but the feeble arguments of
the opponents showed how untenable the old theory had become. In 1648
Pascal suggested that if the theory of the pressure of air upon the mercury
was correct, it could be demonstrated by ascending a mountain with the
mercury tube. As the air was known to get progressively lighter from base
to summit, the height of the column should be progressively lessened as the
ascent was made, and increase again on the descent into the denser air. The
experiment was made on the mountain called the Puy-de-Dome, in
Auvergne, and the column of mercury fell and rose progressively through a
space of about three inches as the ascent and descent were made.
This experiment practically sealed the verdict on the new theory, but it
also suggested something more. If the mercury descended to a certain mark
on the scale on a mountain-top whose height was known, why was not this
a means of measuring the heights of all other elevations? And so the
beginning was made which, with certain modifications and corrections in
details, is now the basis of barometrical measurements of heights.
In hydraulics, also, Torricelli seems to have taken one of the first steps.
He did this by showing that the water which issues from a hole in the side
or bottom of a vessel does so at the same velocity as that which a body

would acquire by falling from the level of the surface of the water to that of
the orifice. This discovery was of the greatest importance to a correct
understanding of the science of the motions of fluids. He also discovered
the valuable mechanical principle that if any number of bodies be connected
so that by their motion there is neither ascent nor descent of their centre of
gravity, these bodies are in equilibrium.
Besides making these discoveries, he greatly improved the microscope
and the telescope, and invented a simple microscope made of a globule of
glass. In 1644 he published a tract on the properties of the cycloid in which
he suggested a solution of the problem of its quadrature. As soon as this
pamphlet appeared its author was accused by Gilles Roberval (1602-1675)
of having appropriated a solution already offered by him. This led to a long
debate, during which Torricelli was seized with a fever, from the effects of
which he died, in Florence, October 25, 1647. There is reason to believe,
however, that while Roberval's discovery was made before Torricelli's, the
latter reached his conclusions independently.

VI. TWO PSEUDO-SCIENCES—ALCHEMY
AND ASTROLOGY
In recent chapters we have seen science come forward with tremendous
strides. A new era is obviously at hand. But we shall misconceive the spirit
of the times if we fail to understand that in the midst of all this progress
there was still room for mediaeval superstition and for the pursuit of
fallacious ideals. Two forms of pseudo-science were peculiarly prevalent—
alchemy and astrology. Neither of these can with full propriety be called a
science, yet both were pursued by many of the greatest scientific workers of
the period. Moreover, the studies of the alchemist may with some propriety
be said to have laid the foundation for the latter-day science of chemistry;
while astrology was closely allied to astronomy, though its relations to that
science are not as intimate as has sometimes been supposed.
Just when the study of alchemy began is undetermined. It was certainly
of very ancient origin, perhaps Egyptian, but its most flourishing time was
from about the eighth century A.D. to the eighteenth century. The stories of
the Old Testament formed a basis for some of the strange beliefs regarding
the properties of the magic "elixir," or "philosopher's stone." Alchemists
believed that most of the antediluvians, perhaps all of them, possessed a
knowledge of this stone. How, otherwise, could they have prolonged their
lives to nine and a half centuries? And Moses was surely a first-rate
alchemist, as is proved by the story of the Golden Calf.(1) After Aaron had
made the calf of gold, Moses performed the much more difficult task of
grinding it to powder and "strewing it upon the waters," thus showing that
he had transmuted it into some lighter substance.
But antediluvians and Biblical characters were not the only persons who
were thought to have discovered the coveted "elixir." Hundreds of aged
mediaeval chemists were credited with having made the discovery, and
were thought to be living on through the centuries by its means. Alaies de
Lisle, for example, who died in 1298, at the age of 110, was alleged to have
been at the point of death at the age of fifty, but just at this time he made the
fortunate discovery of the magic stone, and so continued to live in health

and affluence for sixty years more. And De Lisle was but one case among
hundreds.
An aged and wealthy alchemist could claim with seeming plausibility
that he was prolonging his life by his magic; whereas a younger man might
assert that, knowing the great secret, he was keeping himself young through
the centuries. In either case such a statement, or rumor, about a learned and
wealthy alchemist was likely to be believed, particularly among strangers;
and as such a man would, of course, be the object of much attention, the
claim was frequently made by persons seeking notoriety. One of the most
celebrated of these impostors was a certain Count de Saint-Germain, who
was connected with the court of Louis XV. His statements carried the more
weight because, having apparently no means of maintenance, he continued
to live in affluence year after year—for two thousand years, as he himself
admitted—by means of the magic stone. If at any time his statements were
doubted, he was in the habit of referring to his valet for confirmation, this
valet being also under the influence of the elixir of life.
"Upon one occasion his master was telling a party of ladies and
gentlemen, at dinner, some conversation he had had in Palestine, with King
Richard I., of England, whom he described as a very particular friend of his.
Signs of astonishment and incredulity were visible on the faces of the
company, upon which Saint-Germain very coolly turned to his servant, who
stood behind his chair, and asked him if he had not spoken the truth. 'I
really cannot say,' replied the man, without moving a muscle; 'you forget,
sir, I have been only five hundred years in your service.' 'Ah, true,' said his
master, 'I remember now; it was a little before your time!'"(2)
In the time of Saint-Germain, only a little over a century ago, belief in
alchemy had almost disappeared, and his extraordinary tales were probably
regarded in the light of amusing stories. Still there was undoubtedly a
lingering suspicion in the minds of many that this man possessed some
peculiar secret. A few centuries earlier his tales would hardly have been
questioned, for at that time the belief in the existence of this magic
something was so strong that the search for it became almost a form of
mania; and once a man was seized with it, lie gambled away health,
position, and life itself in pursuing the coveted stake. An example of this is
seen in Albertus Magnus, one of the most learned men of his time, who it is

said resigned his position as bishop of Ratisbon in order that he might
pursue his researches in alchemy.
If self-sacrifice was not sufficient to secure the prize, crime would
naturally follow, for there could be no limit to the price of the stakes in this
game. The notorious Marechal de Reys, failing to find the coveted stone by
ordinary methods of laboratory research, was persuaded by an impostor that
if he would propitiate the friendship of the devil the secret would be
revealed. To this end De Reys began secretly capturing young children as
they passed his castle and murdering them. When he was at last brought to
justice it was proved that he had murdered something like a hundred
children within a period of three years. So, at least, runs one version of the
story of this perverted being.
Naturally monarchs, constantly in need of funds, were interested in these
alchemists. Even sober England did not escape, and Raymond Lully, one of
the most famous of the thirteenth and fourteenth century alchemists, is said
to have been secretly invited by King Edward I. (or II.) to leave Milan and
settle in England. According to some accounts, apartments were assigned to
his use in the Tower of London, where he is alleged to have made some six
million pounds sterling for the monarch, out of iron, mercury, lead, and
pewter.
Pope John XXII., a friend and pupil of the alchemist Arnold de
Villeneuve, is reported to have learned the secrets of alchemy from his
master. Later he issued two bulls against "pretenders" in the art, which, far
from showing his disbelief, were cited by alchemists as proving that he
recognized pretenders as distinct from true masters of magic.
To moderns the attitude of mind of the alchemist is difficult to
comprehend. It is, perhaps, possible to conceive of animals or plants
possessing souls, but the early alchemist attributed the same thing—or
something kin to it—to metals also. Furthermore, just as plants germinated
from seeds, so metals were supposed to germinate also, and hence a
constant growth of metals in the ground. To prove this the alchemist cited
cases where previously exhausted gold-mines were found, after a lapse of
time, to contain fresh quantities of gold. The "seed" of the remaining
particles of gold had multiplied and increased. But this germinating process
could only take place under favorable conditions, just as the seed of a plant
must have its proper surroundings before germinating; and it was believed

that the action of the philosopher's stone was to hasten this process, as man
may hasten the growth of plants by artificial means. Gold was looked upon
as the most perfect metal, and all other metals imperfect, because not yet
"purified." By some alchemists they were regarded as lepers, who, when
cured of their leprosy, would become gold. And since nature intended that
all things should be perfect, it was the aim of the alchemist to assist her in
this purifying process, and incidentally to gain wealth and prolong his life.
By other alchemists the process of transition from baser metals into gold
was conceived to be like a process of ripening fruit. The ripened product
was gold, while the green fruit, in various stages of maturity, was
represented by the base metals. Silver, for example, was more nearly ripe
than lead; but the difference was only one of "digestion," and it was thought
that by further "digestion" lead might first become silver and eventually
gold. In other words, Nature had not completed her work, and was wofully
slow at it at best; but man, with his superior faculties, was to hasten the
process in his laboratories—if he could but hit upon the right method of
doing so.
It should not be inferred that the alchemist set about his task of assisting
nature in a haphazard way, and without training in the various alchemic
laboratory methods. On the contrary, he usually served a long
apprenticeship in the rudiments of his calling. He was obliged to learn, in a
general way, many of the same things that must be understood in either
chemical or alchemical laboratories. The general knowledge that certain
liquids vaporize at lower temperatures than others, and that the melting-
points of metals differ greatly, for example, was just as necessary to
alchemy as to chemistry. The knowledge of the gross structure, or nature, of
materials was much the same to the alchemist as to the chemist, and, for
that matter, many of the experiments in calcining, distilling, etc., were
practically identical.
To the alchemist there were three principles—salt, sulphur, and mercury
—and the sources of these principles were the four elements—earth, water,
fire, and air. These four elements were accountable for every substance in
nature. Some of the experiments to prove this were so illusive, and yet
apparently so simple, that one is not surprised that it took centuries to
disprove them. That water was composed of earth and air seemed easily
proven by the simple process of boiling it in a tea-kettle, for the residue left

was obviously an earthy substance, whereas the steam driven off was
supposed to be air. The fact that pure water leaves no residue was not
demonstrated until after alchemy had practically ceased to exist. It was
possible also to demonstrate that water could be turned into fire by thrusting
a red-hot poker under a bellglass containing a dish of water. Not only did
the quantity of water diminish, but, if a lighted candle was thrust under the
glass, the contents ignited and burned, proving, apparently, that water had
been converted into fire. These, and scores of other similar experiments,
seemed so easily explained, and to accord so well with the "four elements"
theory, that they were seldom questioned until a later age of inductive
science.
But there was one experiment to which the alchemist pinned his faith in
showing that metals could be "killed" and "revived," when proper means
were employed. It had been known for many centuries that if any metal,
other than gold or silver, were calcined in an open crucible, it turned, after a
time, into a peculiar kind of ash. This ash was thought by the alchemist to
represent the death of the metal. But if to this same ash a few grains of
wheat were added and heat again applied to the crucible, the metal was seen
to "rise from its ashes" and resume its original form—a well-known
phenomenon of reducing metals from oxides by the use of carbon, in the
form of wheat, or, for that matter, any other carbonaceous substance. Wheat
was, therefore, made the symbol of the resurrection of the life eternal. Oats,
corn, or a piece of charcoal would have "revived" the metals from the ashes
equally well, but the mediaeval alchemist seems not to have known this.
However, in this experiment the metal seemed actually to be destroyed and
revivified, and, as science had not as yet explained this striking
phenomenon, it is little wonder that it deceived the alchemist.
Since the alchemists pursued their search of the magic stone in such a
methodical way, it would seem that they must have some idea of the
appearance of the substance they sought. Probably they did, each according
to his own mental bias; but, if so, they seldom committed themselves to
writing, confining their discourses largely to speculations as to the
properties of this illusive substance. Furthermore, the desire for secrecy
would prevent them from expressing so important a piece of information.
But on the subject of the properties, if not on the appearance of the
"essence," they were voluminous writers. It was supposed to be the only
perfect substance in existence, and to be confined in various substances, in

quantities proportionate to the state of perfection of the substance. Thus,
gold being most nearly perfect would contain more, silver less, lead still
less, and so on. The "essence" contained in the more nearly perfect metals
was thought to be more potent, a very small quantity of it being capable of
creating large quantities of gold and of prolonging life indefinitely.
It would appear from many of the writings of the alchemists that their
conception of nature and the supernatural was so confused and entangled in
an inexplicable philosophy that they themselves did not really understand
the meaning of what they were attempting to convey. But it should not be
forgotten that alchemy was kept as much as possible from the ignorant
general public, and the alchemists themselves had knowledge of secret
words and expressions which conveyed a definite meaning to one of their
number, but which would appear a meaningless jumble to an outsider. Some
of these writers declared openly that their writings were intended to convey
an entirely erroneous impression, and were sent out only for that purpose.
However, while it may have been true that the vagaries of their writings
were made purposely, the case is probably more correctly explained by
saying that the very nature of the art made definite statements impossible.
They were dealing with something that did not exist—could not exist. Their
attempted descriptions became, therefore, the language of romance rather
than the language of science.
But if the alchemists themselves were usually silent as to the appearance
of the actual substance of the philosopher's stone, there were numberless
other writers who were less reticent. By some it was supposed to be a stone,
by others a liquid or elixir, but more commonly it was described as a black
powder. It also possessed different degrees of efficiency according to its
degrees of purity, certain forms only possessing the power of turning base
metals into gold, while others gave eternal youth and life or different
degrees of health. Thus an alchemist, who had made a partial discovery of
this substance, could prolong life a certain number of years only, or,
possessing only a small and inadequate amount of the magic powder, he
was obliged to give up the ghost when the effect of this small quantity had
passed away.
This belief in the supernatural power of the philosopher's stone to
prolong life and heal diseases was probably a later phase of alchemy,
possibly developed by attempts to connect the power of the mysterious

essence with Biblical teachings. The early Roman alchemists, who claimed
to be able to transmute metals, seem not to have made other claims for their
magic stone.
By the fifteenth century the belief in the philosopher's stone had become
so fixed that governments began to be alarmed lest some lucky possessor of
the secret should flood the country with gold, thus rendering the existing
coin of little value. Some little consolation was found in the thought that in
case all the baser metals were converted into gold iron would then become
the "precious metal," and would remain so until some new philosopher's
stone was found to convert gold back into iron—a much more difficult feat,
it was thought. However, to be on the safe side, the English Parliament, in
1404, saw fit to pass an act declaring the making of gold and silver to be a
felony. Nevertheless, in 1455, King Henry VI. granted permission to several
"knights, citizens of London, chemists, and monks" to find the philosopher's
stone, or elixir, that the crown might thus be enabled to pay off its debts.
The monks and ecclesiastics were supposed to be most likely to discover
the secret process, since "they were such good artists in transubstantiating
bread and wine."
In Germany the emperors Maximilian I., Rudolf II., and Frederick II.
gave considerable attention to the search, and the example they set was
followed by thousands of their subjects. It is said that some noblemen
developed the unpleasant custom of inviting to their courts men who were
reputed to have found the stone, and then imprisoning the poor alchemists
until they had made a certain quantity of gold, stimulating their activity
with tortures of the most atrocious kinds. Thus this danger of being
imprisoned and held for ransom until some fabulous amount of gold should
be made became the constant menace of the alchemist. It was useless for an
alchemist to plead poverty once it was noised about that he had learned the
secret. For how could such a man be poor when, with a piece of metal and a
few grains of magic powder, he was able to provide himself with gold? It
was, therefore, a reckless alchemist indeed who dared boast that he had
made the coveted discovery.
The fate of a certain indiscreet alchemist, supposed by many to have been
Seton, a Scotchman, was not an uncommon one. Word having been brought
to the elector of Saxony that this alchemist was in Dresden and boasting of
his powers, the elector caused him to be arrested and imprisoned. Forty

guards were stationed to see that he did not escape and that no one visited
him save the elector himself. For some time the elector tried by argument
and persuasion to penetrate his secret or to induce him to make a certain
quantity of gold; but as Seton steadily refused, the rack was tried, and for
several months he suffered torture, until finally, reduced to a mere skeleton,
he was rescued by a rival candidate of the elector, a Pole named Michael
Sendivogins, who drugged the guards. However, before Seton could be
"persuaded" by his new captor, he died of his injuries.
But Sendivogins was also ambitious in alchemy, and, since Seton was
beyond his reach, he took the next best step and married his widow. From
her, as the story goes, he received an ounce of black powder—the veritable
philosopher's stone. With this he manufactured great quantities of gold,
even inviting Emperor Rudolf II. to see him work the miracle. That
monarch was so impressed that he caused a tablet to be inserted in the wall
of the room in which he had seen the gold made.
Sendivogins had learned discretion from the misfortune of Seton, so that
he took the precaution of concealing most of the precious powder in a secret
chamber of his carriage when he travelled, having only a small quantity
carried by his steward in a gold box. In particularly dangerous places, he is
said to have exchanged clothes with his coachman, making the servant take
his place in the carriage while he mounted the box.
About the middle of the seventeenth century alchemy took such firm root
in the religious field that it became the basis of the sect known as the
Rosicrucians. The name was derived from the teaching of a German
philosopher, Rosenkreutz, who, having been healed of a dangerous illness
by an Arabian supposed to possess the philosopher's stone, returned home
and gathered about him a chosen band of friends, to whom he imparted the
secret. This sect came rapidly into prominence, and for a short time at least
created a sensation in Europe, and at the time were credited with having
"refined and spiritualized" alchemy. But by the end of the seventeenth
century their number had dwindled to a mere handful, and henceforth they
exerted little influence.
Another and earlier religious sect was the Aureacrucians, founded by
Jacob Bohme, a shoemaker, born in Prussia in 1575. According to his
teachings the philosopher's stone could be discovered by a diligent search of
the Old and the New Testaments, and more particularly the Apocalypse,

which contained all the secrets of alchemy. This sect found quite a number
of followers during the life of Bohme, but gradually died out after his death;
not, however, until many of its members had been tortured for heresy, and
one at least, Kuhlmann, of Moscow, burned as a sorcerer.
The names of the different substances that at various times were thought
to contain the large quantities of the "essence" during the many centuries of
searching for it, form a list of practically all substances that were known,
discovered, or invented during the period. Some believed that acids
contained the substance; others sought it in minerals or in animal or
vegetable products; while still others looked to find it among the distilled
"spirits"—the alcoholic liquors and distilled products. On the introduction
of alcohol by the Arabs that substance became of all-absorbing interest, and
for a long time allured the alchemist into believing that through it they were
soon to be rewarded. They rectified and refined it until "sometimes it was
so strong that it broke the vessels containing it," but still it failed in its
magic power. Later, brandy was substituted for it, and this in turn discarded
for more recent discoveries.
There were always, of course, two classes of alchemists: serious
investigators whose honesty could not be questioned, and clever impostors
whose legerdemain was probably largely responsible for the extended belief
in the existence of the philosopher's stone. Sometimes an alchemist
practised both, using the profits of his sleight-of-hand to procure the means
of carrying on his serious alchemical researches. The impostures of some of
these jugglers deceived even the most intelligent and learned men of the
time, and so kept the flame of hope constantly burning. The age of cold
investigation had not arrived, and it is easy to understand how an
unscrupulous mediaeval Hermann or Kellar might completely deceive even
the most intelligent and thoughtful scholars. In scoffing at the credulity of
such an age, it should not be forgotten that the "Keely motor" was a late
nineteenth-century illusion.
But long before the belief in the philosopher's stone had died out, the
methods of the legerdemain alchemist had been investigated and reported
upon officially by bodies of men appointed to make such investigations,
although it took several generations completely to overthrow a superstition
that had been handed down through several thousand years. In April of
1772 Monsieur Geoffroy made a report to the Royal Academy of Sciences,

at Paris, on the alchemic cheats principally of the sixteenth and seventeenth
centuries. In this report he explains many of the seemingly marvellous feats
of the unscrupulous alchemists. A very common form of deception was the
use of a double-bottomed crucible. A copper or brass crucible was covered
on the inside with a layer of wax, cleverly painted so as to resemble the
ordinary metal. Between this layer of wax and the bottom of the crucible,
however, was a layer of gold dust or silver. When the alchemist wished to
demonstrate his power, he had but to place some mercury or whatever
substance he chose in the crucible, heat it, throw in a grain or two of some
mysterious powder, pronounce a few equally mysterious phrases to impress
his audience, and, behold, a lump of precious metal would be found in the
bottom of his pot. This was the favorite method of mediocre performers, but
was, of course, easily detected.
An equally successful but more difficult way was to insert surreptitiously
a lump of metal into the mixture, using an ordinary crucible. This required
great dexterity, but was facilitated by the use of many mysterious
ceremonies on the part of the operator while performing, just as the modern
vaudeville performer diverts the attention of the audience to his right hand
while his left is engaged in the trick. Such ceremonies were not questioned,
for it was the common belief that the whole process "lay in the spirit as
much as in the substance," many, as we have seen, regarding the whole
process as a divine manifestation.
Sometimes a hollow rod was used for stirring the mixture in the crucible,
this rod containing gold dust, and having the end plugged either with wax
or soft metal that was easily melted. Again, pieces of lead were used which
had been plugged with lumps of gold carefully covered over; and a very
simple and impressive demonstration was making use of a nugget of gold
that had been coated over with quicksilver and tarnished so as to resemble
lead or some base metal. When this was thrown into acid the coating was
removed by chemical action, leaving the shining metal in the bottom of the
vessel. In order to perform some of these tricks, it is obvious that the
alchemist must have been well supplied with gold, as some of them, when
performing before a royal audience, gave the products to their visitors. But
it was always a paying investment, for once his reputation was established
the gold-maker found an endless variety of ways of turning his alleged
knowledge to account, frequently amassing great wealth.

Some of the cleverest of the charlatans often invited royal or other
distinguished guests to bring with them iron nails to be turned into gold
ones. They were transmuted in the alchemist's crucible before the eyes of
the visitors, the juggler adroitly extracting the iron nail and inserting a gold
one without detection. It mattered little if the converted gold nail differed in
size and shape from the original, for this change in shape could be laid to
the process of transmutation; and even the very critical were hardly likely to
find fault with the exchange thus made. Furthermore, it was believed that
gold possessed the property of changing its bulk under certain conditions,
some of the more conservative alchemists maintaining that gold was only
increased in bulk, not necessarily created, by certain forms of the magic
stone. Thus a very proficient operator was thought to be able to increase a
grain of gold into a pound of pure metal, while one less expert could only
double, or possibly treble, its original weight.
The actual number of useful discoveries resulting from the efforts of the
alchemists is considerable, some of them of incalculable value. Roger
Bacon, who lived in the thirteenth century, while devoting much of his time
to alchemy, made such valuable discoveries as the theory, at least, of the
telescope, and probably gunpowder. Of this latter we cannot be sure that the
discovery was his own and that he had not learned of it through the source
of old manuscripts. But it is not impossible nor improbable that he may
have hit upon the mixture that makes the explosives while searching for the
philosopher's stone in his laboratory. "Von Helmont, in the same pursuit,
discovered the properties of gas," says Mackay; "Geber made discoveries in
chemistry, which were equally important; and Paracelsus, amid his
perpetual visions of the transmutation of metals, found that mercury was a
remedy for one of the most odious and excruciating of all the diseases that
afflict humanity."' As we shall see a little farther on, alchemy finally
evolved into modern chemistry, but not until it had passed through several
important transitional stages.
ASTROLOGY
In a general way modern astronomy may be considered as the outgrowth
of astrology, just as modern chemistry is the result of alchemy. It is quite
possible, however, that astronomy is the older of the two; but astrology
must have developed very shortly after. The primitive astronomer, having
acquired enough knowledge from his observations of the heavenly bodies to

make correct predictions, such as the time of the coming of the new moon,
would be led, naturally, to believe that certain predictions other than purely
astronomical ones could be made by studying the heavens. Even if the
astronomer himself did not believe this, some of his superstitious admirers
would; for to the unscientific mind predictions of earthly events would
surely seem no more miraculous than correct predictions as to the future
movements of the sun, moon, and stars. When astronomy had reached a
stage of development so that such things as eclipses could be predicted with
anything like accuracy, the occult knowledge of the astronomer would be
unquestioned. Turning this apparently occult knowledge to account in a
mercenary way would then be the inevitable result, although it cannot be
doubted that many of the astrologers, in all ages, were sincere in their
beliefs.
Later, as the business of astrology became a profitable one, sincere
astronomers would find it expedient to practise astrology as a means of
gaining a livelihood. Such a philosopher as Kepler freely admitted that he
practised astrology "to keep from starving," although he confessed no faith
in such predictions. "Ye otherwise philosophers," he said, "ye censure this
daughter of astronomy beyond her deserts; know ye not that she must
support her mother by her charms."
Once astrology had become an established practice, any considerable
knowledge of astronomy was unnecessary, for as it was at best but a system
of good guessing as to future events, clever impostors could thrive equally
well without troubling to study astronomy. The celebrated astrologers,
however, were usually astronomers as well, and undoubtedly based many of
their predictions on the position and movements of the heavenly bodies.
Thus, the casting of a horoscope that is, the methods by which the
astrologers ascertained the relative position of the heavenly bodies at the
time of a birth—was a simple but fairly exact procedure. Its basis was the
zodiac, or the path traced by the sun in his yearly course through certain
constellations. At the moment of the birth of a child, the first care of the
astrologer was to note the particular part of the zodiac that appeared on the
horizon. The zodiac was then divided into "houses"—that is, into twelve
spaces—on a chart. In these houses were inserted the places of the planets,
sun, and moon, with reference to the zodiac. When this chart was completed
it made a fairly correct diagram of the heavens and the position of the

heavenly bodies as they would appear to a person standing at the place of
birth at a certain time.
Up to this point the process was a simple one of astronomy. But the next
step—the really important one—that of interpreting this chart, was the one
which called forth the skill and imagination of the astrologer. In this
interpretation, not in his mere observations, lay the secret of his success.
Nor did his task cease with simply foretelling future events that were to
happen in the life of the newly born infant. He must not only point out the
dangers, but show the means whereby they could be averted, and his
prophylactic measures, like his predictions, were alleged to be based on his
reading of the stars.
But casting a horoscope at the time of births was, of course, only a small
part of the astrologer's duty. His offices were sought by persons of all ages
for predictions as to their futures, the movements of an enemy, where to
find stolen goods, and a host of everyday occurrences. In such cases it is
more than probable that the astrologers did very little consulting of the stars
in making their predictions. They became expert physiognomists and
excellent judges of human nature, and were thus able to foretell futures with
the same shrewdness and by the same methods as the modern "mediums,"
palmists, and fortune-tellers. To strengthen belief in their powers, it became
a common thing for some supposedly lost document of the astrologer to be
mysteriously discovered after an important event, this document purporting
to foretell this very event. It was also a common practice with astrologers to
retain, or have access to, their original charts, cleverly altering them from
time to time to fit conditions.
The dangers attendant upon astrology were of such a nature that the lot of
the astrologer was likely to prove anything but an enviable one. As in the
case of the alchemist, the greater the reputation of an astrologer the greater
dangers he was likely to fall into. If he became so famous that he was
employed by kings or noblemen, his too true or too false prophecies were
likely to bring him into disrepute—even to endanger his life.
Throughout the dark age the astrologers flourished, but the sixteenth and
seventeenth centuries were the golden age of these impostors. A skilful
astrologer was as much an essential to the government as the highest
official, and it would have been a bold monarch, indeed, who would

undertake any expedition of importance unless sanctioned by the governing
stars as interpreted by these officials.
It should not be understood, however, that belief in astrology died with
the advent of the Copernican doctrine. It did become separated from
astronomy very shortly after, to be sure, and undoubtedly among the
scientists it lost much of its prestige. But it cannot be considered as entirely
passed away, even to-day, and even if we leave out of consideration street-
corner "astrologers" and fortune-tellers, whose signs may be seen in every
large city, there still remains quite a large class of relatively intelligent
people who believe in what they call "the science of astrology." Needless to
say, such people are not found among the scientific thinkers; but it is
significant that scarcely a year passes that some book or pamphlet is not
published by some ardent believer in astrology, attempting to prove by the
illogical dogmas characteristic of unscientific thinkers that astrology is a
science. The arguments contained in these pamphlets are very much the
same as those of the astrologers three hundred years ago, except that they
lack the quaint form of wording which is one of the features that lends
interest to the older documents. These pamphlets need not be taken
seriously, but they are interesting as exemplifying how difficult it is, even in
an age of science, to entirely stamp out firmly established superstitions.
Here are some of the arguments advanced in defence of astrology, taken
from a little brochure entitled "Astrology Vindicated," published in 1898:
"It will be found that a person born when the Sun is in twenty degrees
Scorpio has the left ear as his exceptional feature and the nose (Sagittarius)
bent towards the left ear. A person born when the Sun is in any of the latter
degrees of Taurus, say the twenty-fifth degree, will have a small, sharp,
weak chin, curved up towards Gemini, the two vertical lines on the upper
lip."(4) The time was when science went out of its way to prove that such
statements were untrue; but that time is past, and such writers are usually
classed among those energetic but misguided persons who are unable to
distinguish between logic and sophistry.
In England, from the time of Elizabeth to the reign of William and Mary,
judicial astrology was at its height. After the great London fire, in 1666, a
committee of the House of Commons publicly summoned the famous
astrologer, Lilly, to come before Parliament and report to them on his
alleged prediction of the calamity that had befallen the city. Lilly, for some
reason best known to himself, denied having made such a prediction, being,

as he explained, "more interested in determining affairs of much more
importance to the future welfare of the country." Some of the explanations
of his interpretations will suffice to show their absurdities, which, however,
were by no means regarded as absurdities at that time, for Lilly was one of
the greatest astrologers of his day. He said that in 1588 a prophecy had been
printed in Greek characters which foretold exactly the troubles of England
between the years 1641. and 1660. "And after him shall come a dreadful
dead man," ran the prophecy, "and with him a royal G of the best blood in
the world, and he shall have the crown and shall set England on the right
way and put out all heresies." His interpretation of this was that, "Monkery
being extinguished above eighty or ninety years, and the Lord General's
name being Monk, is the dead man. The royal G or C (it is gamma in the
Greek, intending C in the Latin, being the third letter in the alphabet) is
Charles II., who, for his extraction, may be said to be of the best blood of
the world."(5)
This may be taken as a fair sample of Lilly's interpretations of
astrological prophesies, but many of his own writings, while somewhat
more definite and direct, are still left sufficiently vague to allow his skilful
interpretations to set right an apparent mistake. One of his famous
documents was "The Starry Messenger," a little pamphlet purporting to
explain the phenomenon of a "strange apparition of three suns" that were
seen in London on November 19, 1644—-the anniversary of the birth of
Charles I., then the reigning monarch. This phenomenon caused a great stir
among the English astrologers, coming, as it did, at a time of great political
disturbance. Prophecies were numerous, and Lilly's brochure is only one of
many that appeared at that time, most of which, however, have been lost.
Lilly, in his preface, says: "If there be any of so prevaricate a judgment as to
think that the apparition of these three Suns doth intimate no Novelle thing
to happen in our own Climate, where they were manifestly visible, I shall
lament their indisposition, and conceive their brains to be shallow, and
voyde of understanding humanity, or notice of common History."
Having thus forgiven his few doubting readers, who were by no means in
the majority in his day, he takes up in review the records of the various
appearances of three suns as they have occurred during the Christian era,
showing how such phenomena have governed certain human events in a
very definite manner. Some of these are worth recording.

"Anno 66. A comet was seen, and also three Suns: In which yeer, Florus
President of the Jews was by them slain. Paul writes to Timothy. The
Christians are warned by a divine Oracle, and depart out of Jerusalem.
Boadice a British Queen, killeth seventy thousand Romans. The Nazareni, a
scurvie Sect, begun, that boasted much of Revelations and Visions. About a
year after Nero was proclaimed enemy to the State of Rome."
Again, "Anno 1157, in September, there were seen three Suns together, in
as clear weather as could be: And a few days after, in the same month, three
Moons, and, in the Moon that stood in the middle, a white Crosse. Sueno,
King of Denmark, at a great Feast, killeth Canutus: Sueno is himself slain,
in pursuit of Waldemar. The Order of Eremites, according to the rule of
Saint Augustine, begun this year; and in the next, the Pope submits to the
Emperour: (was not this miraculous?) Lombardy was also adjudged to the
Emperour."
Continuing this list of peculiar phenomena he comes down to within a
few years of his own time.
"Anno 1622, three Suns appeared at Heidelberg. The woful Calamities
that have ever since fallen upon the Palatinate, we are all sensible of, and of
the loss of it, for any thing I see, for ever, from the right Heir. Osman the
great Turk is strangled that year; and Spinola besiegeth Bergen up Zoom,
etc."
Fortified by the enumeration of these past events, he then proceeds to
make his deductions. "Only this I must tell thee," he writes, "that the
interpretation I write is, I conceive, grounded upon probable foundations;
and who lives to see a few years over his head, will easily perceive I have
unfolded as much as was fit to discover, and that my judgment was not a
mile and a half from truth."
There is a great significance in this "as much as was fit to discover"—a
mysterious something that Lilly thinks it expedient not to divulge. But,
nevertheless, one would imagine that he was about to make some definite
prediction about Charles I., since these three suns appeared upon his
birthday and surely must portend something concerning him. But after
rambling on through many pages of dissertations upon planets and
prophecies, he finally makes his own indefinite prediction.
"O all you Emperors, Kings, Princes, Rulers and Magistrates of Europe,
this unaccustomed Apparition is like the Handwriting in Daniel to some of

you; it premonisheth you, above all other people, to make your peace with
God in time. You shall every one of you smart, and every one of you taste
(none excepted) the heavie hand of God, who will strengthen your subjects
with invincible courage to suppress your misgovernments and Oppressions
in Church or Common-wealth;... Those words are general: a word for my
own country of England.... Look to yourselves; here's some monstrous
death towards you. But to whom? wilt thou say. Herein we consider the
Signe, Lord thereof, and the House; The Sun signifies in that Royal Signe,
great ones; the House signifies captivity, poison, Treachery: From which is
derived thus much, That some very great man, what King, Prince, Duke, or
the like, I really affirm I perfectly know not, shall, I say, come to some such
untimely end."(6)
Here is shown a typical example of astrological prophecy, which seems
to tell something or nothing, according to the point of view of the reader.
According to a believer in astrology, after the execution of Charles I., five
years later, this could be made to seem a direct and exact prophecy. For
example, he says: "You Kings, Princes, etc.,... it premonisheth you... to
make your peace with God.... Look to yourselves; here's some monstrous
death towards you.... That some very great man, what King, Prince,. shall, I
say, come to such untimely end."
But by the doubter the complete prophecy could be shown to be
absolutely indefinite, and applicable as much to the king of France or Spain
as to Charles I., or to any king in the future, since no definite time is stated.
Furthermore, Lilly distinctly states, "What King, Prince, Duke, or the like, I
really affirm I perfectly know not"—which last, at least, was a most truthful
statement. The same ingenuity that made "Gen. Monk" the "dreadful dead
man," could easily make such a prediction apply to the execution of Charles
I. Such a definite statement that, on such and such a day a certain number of
years in the future, the monarch of England would be beheaded—such an
exact statement can scarcely be found in any of the works on astrology. It
should be borne in mind, also, that Lilly was of the Cromwell party and
opposed to the king.
After the death of Charles I., Lilly admitted that the monarch had given
him a thousand pounds to cast his horoscope. "I advised him," says Lilly,
"to proceed eastwards; he went west, and all the world knows the result." It
is an unfortunate thing for the cause of astrology that Lilly failed to mention

this until after the downfall of the monarch. In fact, the sudden death, or
decline in power, of any monarch, even to-day, brings out the perennial
post-mortem predictions of astrologers.
We see how Lilly, an opponent of the king, made his so-called prophecy
of the disaster of the king and his army. At the same time another celebrated
astrologer and rival of Lilly, George Wharton, also made some predictions
about the outcome of the eventful march from Oxford. Wharton, unlike
Lilly, was a follower of the king's party, but that, of course, should have had
no influence in his "scientific" reading of the stars. Wharton's predictions
are much less verbose than Lilly's, much more explicit, and, incidentally,
much more incorrect in this particular instance. "The Moon Lady of the 12,"
he wrote, "and moving betwixt the 8 degree, 34 min., and 21 degree, 26
min. of Aquarius, gives us to understand that His Majesty shall receive
much contentment by certain Messages brought him from foreign parts; and
that he shall receive some sudden and unexpected supply of... by the means
of some that assimilate the condition of his Enemies: And withal this
comfort; that His Majesty shall be exceeding successful in Besieging
Towns, Castles, or Forts, and in persuing the enemy.
"Mars his Sextile to the Sun, Lord of the Ascendant (which happeneth the
18 day of May) will encourage our Soldiers to advance with much alacrity
and cheerfulness of spirit; to show themselves gallant in the most dangerous
attempt.... And now to sum up all: It is most apparent to every impartial and
ingenuous judgment; That although His Majesty cannot expect to be
secured from every trivial disaster that may befall his army, either by the
too much Presumption, Ignorance, or Negligence of some particular
Persons (which is frequently incident and unavoidable in the best of
Armies), yet the several positions of the Heavens duly considered and
compared among themselves, as well in the prefixed Scheme as at the
Quarterly Ingresses, do generally render His Majesty and his whole Army
unexpectedly victorious and successful in all his designs; Believe it
(London), thy Miseries approach, they are like to be many, great, and
grievous, and not to be diverted, unless thou seasonably crave Pardon of
God for being Nurse to this present Rebellion, and speedily submit to thy
Prince's Mercy; Which shall be the daily Prayer of Geo. Wharton."(7)
In the light of after events, it is probable that Wharton's stock as an
astrologer was not greatly enhanced by this document, at least among

members of the Royal family. Lilly's book, on the other hand, became a
favorite with the Parliamentary army.
After the downfall and death of Napoleon there were unearthed many
alleged authentic astrological documents foretelling his ruin. And on the
death of George IV., in 1830, there appeared a document (unknown, as
usual, until that time) purporting to foretell the death of the monarch to the
day, and this without the astrologer knowing that his horoscope was being
cast for a monarch. A full account of this prophecy is told, with full belief,
by Roback, a nineteenth-century astrologer. He says:
"In the year 1828, a stranger of noble mien, advanced in life, but
possessing the most bland manners, arrived at the abode of a celebrated
astrologer in London," asking that the learned man foretell his future. "The
astrologer complied with the request of the mysterious visitor, drew forth
his tables, consulted his ephemeris, and cast the horoscope or celestial map
for the hour and the moment of the inquiry, according to the established
rules of his art.
"The elements of his calculation were adverse, and a feeling of gloom
cast a shade of serious thought, if not dejection, over his countenance.
"'You are of high rank,' said the astrologer, as he calculated and looked on
the stranger, 'and of illustrious title.' The stranger made a graceful
inclination of the head in token of acknowledgment of the complimentary
remarks, and the astrologer proceeded with his mission.
"The celestial signs were ominous of calamity to the stranger, who,
probably observing a sudden change in the countenance of the astrologer,
eagerly inquired what evil or good fortune had been assigned him by the
celestial orbs.
"'To the first part of your inquiry,' said the astrologer, 'I can readily reply.
You have been a favorite of fortune; her smiles on you have been abundant,
her frowns but few; you have had, perhaps now possess, wealth and power;
the impossibility of their accomplishment is the only limit to the fulfilment
of your desires.'"
"'You have spoken truly of the past,' said the stranger. 'I have full faith in
your revelations of the future: what say you of my pilgrimage in this life—
is it short or long?'

"'I regret,' replied the astrologer, in answer to this inquiry, 'to be the
herald of ill, though TRUE, fortune; your sojourn on earth will be short.'
"'How short?' eagerly inquired the excited and anxious stranger.
"'Give me a momentary truce,' said the astrologer; 'I will consult the
horoscope, and may possibly find some mitigating circumstances.'
"Having cast his eyes over the celestial map, and paused for some
moments, he surveyed the countenance of the stranger with great sympathy,
and said, 'I am sorry that I can find no planetary influences that oppose your
destiny—your death will take place in two years.'
"The event justified the astrologic prediction: George IV. died on May
18, 1830, exactly two years from the day on which he had visited the
astrologer."(8)
This makes a very pretty story, but it hardly seems like occult insight that
an astrologer should have been able to predict an early death of a man
nearly seventy years old, or to have guessed that his well-groomed visitor
"had, perhaps now possesses, wealth and power." Here again, however, the
point of view of each individual plays the governing part in determining the
importance of such a document. To the scientist it proves nothing; to the
believer in astrology, everything. The significant thing is that it appeared
shortly AFTER the death of the monarch.
On the Continent astrologers were even more in favor than in England.
Charlemagne, and some of his immediate successors, to be sure, attempted
to exterminate them, but such rulers as Louis XI. and Catherine de' Medici
patronized and encouraged them, and it was many years after the time of
Copernicus before their influence was entirely stamped out even in official
life. There can be no question that what gave the color of truth to many of
the predictions was the fact that so many of the prophecies of sudden deaths
and great conflagrations were known to have come true—in many instances
were made to come true by the astrologer himself. And so it happened that
when the prediction of a great conflagration at a certain time culminated in
such a conflagration, many times a second but less-important burning took
place, in which the ambitious astrologer, or his followers, took a central part
about a stake, being convicted of incendiarism, which they had committed
in order that their prophecies might be fulfilled.
But, on the other hand, these predictions were sometimes turned to
account by interested friends to warn certain persons of approaching

dangers.
For example, a certain astrologer foretold the death of Prince Alexander
de' Medici. He not only foretold the death, but described so minutely the
circumstances that would attend it, and gave such a correct description of
the assassin who should murder the prince, that he was at once suspected of
having a hand in the assassination. It developed later, however, that such
was probably not the case; but that some friend of Prince Alexander,
knowing of the plot to take his life, had induced the astrologer to foretell the
event in order that the prince might have timely warning and so elude the
conspirators.
The cause of the decline of astrology was the growing prevalence of the
new spirit of experimental science. Doubtless the most direct blow was
dealt by the Copernican theory. So soon as this was established, the
recognition of the earth's subordinate place in the universe must have made
it difficult for astronomers to be longer deceived by such coincidences as
had sufficed to convince the observers of a more credulous generation.
Tycho Brahe was, perhaps, the last astronomer of prominence who was a
conscientious practiser of the art of the astrologer.

VII. FROM PARACELSUS TO HARVEY
PARACELSUS

In the year 1526 there appeared a new lecturer on the platform at the
University at Basel—a small, beardless, effeminate-looking person—who
had already inflamed all Christendom with his peculiar philosophy, his
revolutionary methods of treating diseases, and his unparalleled success in
curing them. A man who was to be remembered in after-time by some as the
father of modern chemistry and the founder of modern medicine; by others
as madman, charlatan, impostor; and by still others as a combination of all
these. This soft-cheeked, effeminate, woman-hating man, whose very sex
has been questioned, was Theophrastus von Hohenheim, better known as
Paracelsus (1493-1541).
To appreciate his work, something must be known of the life of the man.
He was born near Maria-Einsiedeln, in Switzerland, the son of a poor
physician of the place. He began the study of medicine under the instruction
of his father, and later on came under the instruction of several learned
churchmen. At the age of sixteen he entered the University of Basel, but,
soon becoming disgusted with the philosophical teachings of the time, he
quitted the scholarly world of dogmas and theories and went to live among
the miners in the Tyrol, in order that he might study nature and men at first
hand. Ordinary methods of study were thrown aside, and he devoted his
time to personal observation—the only true means of gaining useful
knowledge, as he preached and practised ever after. Here he became
familiar with the art of mining, learned the physical properties of minerals,
ores, and metals, and acquired some knowledge of mineral waters. More
important still, he came in contact with such diseases, wounds, and injuries
as miners are subject to, and he tried his hand at the practical treatment of
these conditions, untrammelled by the traditions of a profession in which
his training had been so scant.
Having acquired some empirical skill in treating diseases, Paracelsus set
out wandering from place to place all over Europe, gathering practical
information as he went, and learning more and more of the medicinal

virtues of plants and minerals. His wanderings covered a period of about ten
years, at the end of which time he returned to Basel, where he was soon
invited to give a course of lectures in the university.
These lectures were revolutionary in two respects—they were given in
German instead of time-honored Latin, and they were based upon personal
experience rather than upon the works of such writers as Galen and
Avicenna. Indeed, the iconoclastic teacher spoke with open disparagement
of these revered masters, and openly upbraided his fellow-practitioners for
following their tenets. Naturally such teaching raised a storm of opposition
among the older physicians, but for a time the unparalleled success of
Paracelsus in curing diseases more than offset his unpopularity. Gradually,
however, his bitter tongue and his coarse personality rendered him so
unpopular, even among his patients, that, finally, his liberty and life being
jeopardized, he was obliged to flee from Basel, and became a wanderer. He
lived for brief periods in Colmar, Nuremberg, Appenzell, Zurich, Pfeffers,
Augsburg, and several other cities, until finally at Salzburg his eventful life
came to a close in 1541. His enemies said that he had died in a tavern from
the effects of a protracted debauch; his supporters maintained that he had
been murdered at the instigation of rival physicians and apothecaries.
But the effects of his teachings had taken firm root, and continued to
spread after his death. He had shown the fallibility of many of the teachings
of the hitherto standard methods of treating diseases, and had demonstrated
the advantages of independent reasoning based on observation. In his
Magicum he gives his reasons for breaking with tradition. "I did," he says,
"embrace at the beginning these doctrines, as my adversaries (followers of
Galen) have done, but since I saw that from their procedures nothing
resulted but death, murder, stranglings, anchylosed limbs, paralysis, and so
forth, that they held most diseases incurable.... therefore have I quitted this
wretched art, and sought for truth in any other direction. I asked myself if
there were no such thing as a teacher in medicine, where could I learn this
art best? Nowhere better than the open book of nature, written with God's
own finger." We shall see, however, that this "book of nature" taught
Paracelsus some very strange lessons. Modesty was not one of these. "Now
at this time," he declares, "I, Theophrastus Paracelsus, Bombast, Monarch
of the Arcana, was endowed by God with special gifts for this end, that
every searcher after this supreme philosopher's work may be forced to
imitate and to follow me, be he Italian, Pole, Gaul, German, or whatsoever

or whosoever he be. Come hither after me, all ye philosophers, astronomers,
and spagirists.... I will show and open to you... this corporeal regeneration."
(1)
Paracelsus based his medical teachings on four "pillars"—philosophy,
astronomy, alchemy, and virtue of the physician—a strange-enough
equipment surely, and yet, properly interpreted, not quite so anomalous as it
seems at first blush. Philosophy was the "gate of medicine," whereby the
physician entered rightly upon the true course of learning; astronomy, the
study of the stars, was all-important because "they (the stars) caused disease
by their exhalations, as, for instance, the sun by excessive heat"; alchemy,
as he interpreted it, meant the improvement of natural substances for man's
benefit; while virtue in the physician was necessary since "only the virtuous
are permitted to penetrate into the innermost nature of man and the
universe."
All his writings aim to promote progress in medicine, and to hold before
the physician a grand ideal of his profession. In this his views are wide and
far-reaching, based on the relationship which man bears to nature as a
whole; but in his sweeping condemnations he not only rejected Galenic
therapeutics and Galenic anatomy, but condemned dissections of any kind.
He laid the cause of all diseases at the door of the three mystic elements—
salt, sulphur, and mercury. In health he supposed these to be mingled in the
body so as to be indistinguishable; a slight separation of them produced
disease; and death he supposed to be the result of their complete separation.
The spiritual agencies of diseases, he said, had nothing to do with either
angels or devils, but were the spirits of human beings.
He believed that all food contained poisons, and that the function of
digestion was to separate the poisonous from the nutritious. In the stomach
was an archaeus, or alchemist, whose duty was to make this separation. In
digestive disorders the archaeus failed to do this, and the poisons thus
gaining access to the system were "coagulated" and deposited in the joints
and various other parts of the body. Thus the deposits in the kidneys and
tartar on the teeth were formed; and the stony deposits of gout were
particularly familiar examples of this. All this is visionary enough, yet it
shows at least a groping after rational explanations of vital phenomena.
Like most others of his time, Paracelsus believed firmly in the doctrine of
"signatures"—a belief that every organ and part of the body had a

corresponding form in nature, whose function was to heal diseases of the
organ it resembled. The vagaries of this peculiar doctrine are too numerous
and complicated for lengthy discussion, and varied greatly from generation
to generation. In general, however, the theory may be summed up in the
words of Paracelsus: "As a woman is known by her shape, so are the
medicines." Hence the physicians were constantly searching for some
object of corresponding shape to an organ of the body. The most natural
application of this doctrine would be the use of the organs of the lower
animals for the treatment of the corresponding diseased organs in man.
Thus diseases of the heart were to be treated with the hearts of animals,
liver disorders with livers, and so on. But this apparently simple form of
treatment had endless modifications and restrictions, for not all animals
were useful. For example, it was useless to give the stomach of an ox in
gastric diseases when the indication in such cases was really for the
stomach of a rat. Nor were the organs of animals the only "signatures" in
nature. Plants also played a very important role, and the herb-doctors
devoted endless labor to searching for such plants. Thus the blood-root,
with its red juice, was supposed to be useful in blood diseases, in stopping
hemorrhage, or in subduing the redness of an inflammation.
Paracelsus's system of signatures, however, was so complicated by his
theories of astronomy and alchemy that it is practically beyond
comprehension. It is possible that he himself may have understood it, but it
is improbable that any one else did—as shown by the endless discussions
that have taken place about it. But with all the vagaries of his theories he
was still rational in his applications, and he attacked to good purpose the
complicated "shot-gun" prescriptions of his contemporaries, advocating
more simple methods of treatment.
The ever-fascinating subject of electricity, or, more specifically,
"magnetism," found great favor with him, and with properly adjusted
magnets he claimed to be able to cure many diseases. In epilepsy and
lockjaw, for example, one had but to fasten magnets to the four extremities
of the body, and then, "when the proper medicines were given," the cure
would be effected. The easy loop-hole for excusing failure on the ground of
improper medicines is obvious, but Paracelsus declares that this one
prescription is of more value than "all the humoralists have ever written or
taught."

Since Paracelsus condemned the study of anatomy as useless, he quite
naturally regarded surgery in the same light. In this he would have done far
better to have studied some of his predecessors, such as Galen, Paul of
Aegina, and Avicenna. But instead of "cutting men to pieces," he taught that
surgeons would gain more by devoting their time to searching for the
universal panacea which would cure all diseases, surgical as well as
medical. In this we detect a taint of the popular belief in the philosopher's
stone and the magic elixir of life, his belief in which have been stoutly
denied by some of his followers. He did admit, however, that one operation
alone was perhaps permissible—lithotomy, or the "cutting for stone."
His influence upon medicine rests undoubtedly upon his revolutionary
attitude, rather than on any great or new discoveries made by him. It is
claimed by many that he brought prominently into use opium and mercury,
and if this were indisputably proven his services to medicine could hardly
be overestimated. Unfortunately, however, there are good grounds for
doubting that he was particularly influential in reintroducing these
medicines. His chief influence may perhaps be summed up in a single
phrase—he overthrew old traditions.
To Paracelsus's endeavors, however, if not to the actual products of his
work, is due the credit of setting in motion the chain of thought that
developed finally into scientific chemistry. Nor can the ultimate aim of the
modern chemist seek a higher object than that of this sixteenth-century
alchemist, who taught that "true alchemy has but one aim and object, to
extract the quintessence of things, and to prepare arcana, tinctures, and
elixirs which may restore to man the health and soundness he has lost."
THE GREAT ANATOMISTS
About the beginning of the sixteenth century, while Paracelsus was
scoffing at the study of anatomy as useless, and using his influence against
it, there had already come upon the scene the first of the great anatomists
whose work was to make the century conspicuous in that branch of
medicine.
The young anatomist Charles etienne (1503-1564) made one of the first
noteworthy discoveries, pointing out for the first time that the spinal cord
contains a canal, continuous throughout its length. He also made other
minor discoveries of some importance, but his researches were completely
overshadowed and obscured by the work of a young Fleming who came

upon the scene a few years later, and who shone with such brilliancy in the
medical world that he obscured completely the work of his contemporary
until many years later. This young physician, who was destined to lead such
an eventful career and meet such an untimely end as a martyr to science,
was Andrew Vesalius (1514-1564), who is called the "greatest of
anatomists." At the time he came into the field medicine was struggling
against the dominating Galenic teachings and the theories of Paracelsus, but
perhaps most of all against the superstitions of the time. In France human
dissections were attended with such dangers that the young Vesalius
transferred his field of labors to Italy, where such investigations were
covertly permitted, if not openly countenanced.
From the very start the young Fleming looked askance at the accepted
teachings of the day, and began a series of independent investigations based
upon his own observations. The results of these investigations he gave in a
treatise on the subject which is regarded as the first comprehensive and
systematic work on human anatomy. This remarkable work was published
in the author's twenty-eighth or twenty-ninth year. Soon after this Vesalius
was invited as imperial physician to the court of Emperor Charles V. He
continued to act in the same capacity at the court of Philip II., after the
abdication of his patron. But in spite of this royal favor there was at work a
factor more powerful than the influence of the monarch himself—an
instrument that did so much to retard scientific progress, and by which so
many lives were brought to a premature close.
Vesalius had received permission from the kinsmen of a certain grandee
to perform an autopsy. While making his observations the heart of the
outraged body was seen to palpitate—so at least it was reported. This was
brought immediately to the attention of the Inquisition, and it was only by
the intervention of the king himself that the anatomist escaped the usual fate
of those accused by that tribunal. As it was, he was obliged to perform a
pilgrimage to the Holy Land. While returning from this he was
shipwrecked, and perished from hunger and exposure on the island of
Zante.
At the very time when the anatomical writings of Vesalius were startling
the medical world, there was living and working contemporaneously
another great anatomist, Eustachius (died 1574), whose records of his
anatomical investigations were ready for publication only nine years after

the publication of the work of Vesalius. Owing to the unfortunate
circumstances of the anatomist, however, they were never published during
his lifetime—not, in fact, until 1714. When at last they were given to the
world as Anatomical Engravings, they showed conclusively that Eustachius
was equal, if not superior to Vesalius in his knowledge of anatomy. It has
been said of this remarkable collection of engravings that if they had been
published when they were made in the sixteenth century, anatomy would
have been advanced by at least two centuries. But be this as it may, they
certainly show that their author was a most careful dissector and observer.
Eustachius described accurately for the first time certain structures of the
middle ear, and rediscovered the tube leading from the ear to the throat that
bears his name. He also made careful studies of the teeth and the
phenomena of first and second dentition. He was not baffled by the
minuteness of structures and where he was unable to study them with the
naked eye he used glasses for the purpose, and resorted to macerations and
injections for the study of certain complicated structures. But while the fruit
of his pen and pencil were lost for more than a century after his death, the
effects of his teachings were not; and his two pupils, Fallopius and
Columbus, are almost as well known to-day as their illustrious teacher.
Columbus (1490-1559) did much in correcting the mistakes made in the
anatomy of the bones as described by Vesalius. He also added much to the
science by giving correct accounts of the shape and cavities of the heart,
and made many other discoveries of minor importance. Fallopius (1523-
1562) added considerably to the general knowledge of anatomy, made
several discoveries in the anatomy of the ear, and also several organs in the
abdominal cavity.
At this time a most vitally important controversy was in progress as to
whether or not the veins of the bodies were supplied with valves, many
anatomists being unable to find them. Etienne had first described these
structures, and Vesalius had confirmed his observations. It would seem as if
there could be no difficulty in settling the question as to the fact of such
valves being present in the vessels, for the demonstration is so simple that it
is now made daily by medical students in all physiological laboratories and
dissecting-rooms. But many of the great anatomists of the sixteenth century
were unable to make this demonstration, even when it had been brought to
their attention by such an authority as Vesalius. Fallopius, writing to
Vesalius on the subject in 1562, declared that he was unable to find such

valves. Others, however, such as Eustachius and Fabricius (1537-1619),
were more successful, and found and described these structures. But the
purpose served by these valves was entirely misinterpreted. That they act in
preventing the backward flow of the blood in the veins on its way to the
heart, just as the valves of the heart itself prevent regurgitation, has been
known since the time of Harvey; but the best interpretation that could be
given at that time, even by such a man as Fabricius, was that they acted in
retarding the flow of the blood as it comes from the heart, and thus prevent
its too rapid distribution throughout the body. The fact that the blood might
have been going towards the heart, instead of coming from it, seems never
to have been considered seriously until demonstrated so conclusively by
Harvey.
Of this important and remarkable controversy over the valves in veins,
Withington has this to say: "This is truly a marvellous story. A great Galenic
anatomist is first to give a full and correct description of the valves and
their function, but fails to see that any modification of the old view as to the
motion of the blood is required. Two able dissectors carefully test their
action by experiment, and come to a result, the exact reverse of the truth.
Urged by them, the two foremost anatomists of the age make a special
search for valves and fail to find them. Finally, passing over lesser
peculiarities, an aged and honorable professor, who has lived through all
this, calmly asserts that no anatomist, ancient or modern, has ever
mentioned valves in veins till he discovered them in 1574!"(2)
Among the anatomists who probably discovered these valves was
Michael Servetus (1511-1553); but if this is somewhat in doubt, it is certain
that he discovered and described the pulmonary circulation, and had a very
clear idea of the process of respiration as carried on in the lungs. The
description was contained in a famous document sent to Calvin in 1545—a
document which the reformer carefully kept for seven years in order that he
might make use of some of the heretical statements it contained to
accomplish his desire of bringing its writer to the stake. The awful fate of
Servetus, the interesting character of the man, and the fact that he came so
near to anticipating the discoveries of Harvey make him one of the most
interesting figures in medical history.
In this document which was sent to Calvin, Servetus rejected the doctrine
of natural, vital, and animal spirits, as contained in the veins, arteries, and

nerves respectively, and made the all-important statement that the fluids
contained in veins and arteries are the same. He showed also that the blood
is "purged from fume" and purified by respiration in the lungs, and declared
that there is a new vessel in the lungs, "formed out of vein and artery." Even
at the present day there is little to add to or change in this description of
Servetus's.
By keeping this document, pregnant with advanced scientific views, from
the world, and in the end only using it as a means of destroying its author,
the great reformer showed the same jealousy in retarding scientific progress
as had his arch-enemies of the Inquisition, at whose dictates Vesalius
became a martyr to science, and in whose dungeons etienne perished.
THE COMING OF HARVEY
The time was ripe for the culminating discovery of the circulation of the
blood; but as yet no one had determined the all-important fact that there are
two currents of blood in the body, one going to the heart, one coming from
it. The valves in the veins would seem to show conclusively that the venous
current did not come from the heart, and surgeons must have observed
thousands of times the every-day phenomenon of congested veins at the
distal extremity of a limb around which a ligature or constriction of any
kind had been placed, and the simultaneous depletion of the vessels at the
proximal points above the ligature. But it should be remembered that
inductive science was in its infancy. This was the sixteenth, not the
nineteenth century, and few men had learned to put implicit confidence in
their observations and convictions when opposed to existing doctrines. The
time was at hand, however, when such a man was to make his appearance,
and, as in the case of so many revolutionary doctrines in science, this man
was an Englishman. It remained for William Harvey (1578-1657) to solve
the great mystery which had puzzled the medical world since the beginning
of history; not only to solve it, but to prove his case so conclusively and so
simply that for all time his little booklet must he handed down as one of the
great masterpieces of lucid and almost faultless demonstration.
Harvey, the son of a prosperous Kentish yeoman, was born at Folkestone.
His education was begun at the grammar-school of Canterbury, and later he
became a pensioner of Caius College, Cambridge. Soon after taking his
degree of B.A., at the age of nineteen, he decided upon the profession of
medicine, and went to Padua as a pupil of Fabricius and Casserius.

Returning to England at the age of twenty-four, he soon after (1609)
obtained the reversion of the post of physician to St. Bartholomew's
Hospital, his application being supported by James I. himself. Even at this
time he was a popular physician, counting among his patients such men as
Francis Bacon. In 1618 he was appointed physician extraordinary to the
king, and, a little later, physician in ordinary. He was in attendance upon
Charles I. at the battle of Edgehill, in 1642, where, with the young Prince of
Wales and the Duke of York, after seeking shelter under a hedge, he drew a
book out of his pocket and, forgetful of the battle, became absorbed in
study, until finally the cannon-balls from the enemy's artillery made him
seek a more sheltered position.
On the fall of Charles I. he retired from practice, and lived in retirement
with his brother. He was then well along in years, but still pursued his
scientific researches with the same vigor as before, directing his attention
chiefly to the study of embryology. On June 3, 1657, he was attacked by
paralysis and died, in his eightieth year. He had lived to see his theory of the
circulation accepted, several years before, by all the eminent anatomists of
the civilized world.
A keenness in the observation of facts, characteristic of the mind of the
man, had led Harvey to doubt the truth of existing doctrines as to the
phenomena of the circulation. Galen had taught that "the arteries are filled,
like bellows, because they are expanded," but Harvey thought that the
action of spurting blood from a severed vessel disproved this. For the
spurting was remittant, "now with greater, now with less impetus," and its
greater force always corresponded to the expansion (diastole), not the
contraction (systole) of the vessel. Furthermore, it was evident that
contraction of the heart and the arteries was not simultaneous, as was
commonly taught, because in that case there would be no marked
propulsion of the blood in any direction; and there was no gainsaying the
fact that the blood was forcibly propelled in a definite direction, and that
direction away from the heart.
Harvey's investigations led him to doubt also the accepted theory that
there was a porosity in the septum of tissue that divides the two ventricles
of the heart. It seemed unreasonable to suppose that a thick fluid like the
blood could find its way through pores so small that they could not be
demonstrated by any means devised by man. In evidence that there could be

no such openings he pointed out that, since the two ventricles contract at the
same time, this process would impede rather than facilitate such an intra-
ventricular passage of blood. But what seemed the most conclusive proof of
all was the fact that in the foetus there existed a demonstrable opening
between the two ventricles, and yet this is closed in the fully developed
heart. Why should Nature, if she intended that blood should pass between
the two cavities, choose to close this opening and substitute microscopic
openings in place of it? It would surely seem more reasonable to have the
small perforations in the thin, easily permeable membrane of the foetus, and
the opening in the adult heart, rather than the reverse. From all this Harvey
drew his correct conclusions, declaring earnestly, "By Hercules, there ARE
no such porosities, and they cannot be demonstrated."
Having convinced himself that no intra-ventricular opening existed, he
proceeded to study the action of the heart itself, untrammelled by too much
faith in established theories, and, as yet, with no theory of his own. He soon
discovered that the commonly accepted theory of the heart striking against
the chest-wall during the period of relaxation was entirely wrong, and that
its action was exactly the reverse of this, the heart striking the chest-wall
during contraction. Having thus disproved the accepted theory concerning
the heart's action, he took up the subject of the action of arteries, and soon
was able to demonstrate by vivisection that the contraction of the arteries
was not simultaneous with contractions of the heart. His experiments
demonstrated that these vessels were simply elastic tubes whose pulsations
were "nothing else than the impulse of the blood within them." The reason
that the arterial pulsation was not simultaneous with the heart-beat he found
to be because of the time required to carry the impulse along the tube.
By a series of further careful examinations and experiments, which are
too extended to be given here, he was soon able further to demonstrate the
action and course of the blood during the contractions of the heart. His
explanations were practically the same as those given to-day—first the
contraction of the auricle, sending blood into the ventricle; then ventricular
contraction, making the pulse, and sending the blood into the arteries. He
had thus demonstrated what had not been generally accepted before, that
the heart was an organ for the propulsion of blood. To make such a
statement to-day seems not unlike the sober announcement that the earth is
round or that the sun does not revolve about it. Before Harvey's time,
however, it was considered as an organ that was "in some mysterious way

the source of vitality and warmth, as an animated crucible for the
concoction of blood and the generation of vital spirits."(3)
In watching the rapid and ceaseless contractions of the heart, Harvey was
impressed with the fact that, even if a very small amount of blood was sent
out at each pulsation, an enormous quantity must pass through the organ in
a day, or even in an hour. Estimating the size of the cavities of the heart, and
noting that at least a drachm must be sent out with each pulsation, it was
evident that the two thousand beats given by a very slow human heart in an
hour must send out some forty pounds of blood—more than twice the
amount in the entire body. The question was, what became of it all? For it
should be remembered that the return of the blood by the veins was
unknown, and nothing like a "circulation" more than vaguely conceived
even by Harvey himself. Once it could be shown that the veins were
constantly returning blood to the heart, the discovery that the blood in some
way passes from the arteries to the veins was only a short step. Harvey, by
resorting to vivisections of lower animals and reptiles, soon demonstrated
beyond question the fact that the veins do carry the return blood. "But this,
in particular, can be shown clearer than daylight," says Harvey. "The vena
cava enters the heart at an inferior portion, while the artery passes out
above. Now if the vena cava be taken up with forceps or the thumb and
finger, and the course of the blood intercepted for some distance below the
heart, you will at once see it almost emptied between the fingers and the
heart, the blood being exhausted by the heart's pulsation, the heart at the
same time becoming much paler even in its dilatation, smaller in size,
owing to the deficiency of blood, and at length languid in pulsation, as if
about to die. On the other hand, when you release the vein the heart
immediately regains its color and dimensions. After that, if you leave the
vein free and tie and compress the arteries at some distance from the heart,
you will see, on the contrary, their included portion grow excessively turgid,
the heart becoming so beyond measure, assuming a dark-red color, even to
lividity, and at length so overloaded with blood as to seem in danger of
suffocation; but when the obstruction is removed it returns to its normal
condition, in size, color, and movement."(4)
This conclusive demonstration that the veins return the blood to the heart
must have been most impressive to Harvey, who had been taught to believe
that the blood current in the veins pursued an opposite course, and must
have tended to shake his faith in all existing doctrines of the day.

His next step was the natural one of demonstrating that the blood passes
from the arteries to the veins. He demonstrated conclusively that this did
occur, but for once his rejection of the ancient writers and one modern one
was a mistake. For Galen had taught, and had attempted to demonstrate,
that there are sets of minute vessels connecting the arteries and the veins;
and Servetus had shown that there must be such vessels, at least in the
lungs.
However, the little flaw in the otherwise complete demonstration of
Harvey detracts nothing from the main issue at stake. It was for others who
followed to show just how these small vessels acted in effecting the transfer
of the blood from artery to vein, and the grand general statement that such a
transfer does take place was, after all, the all-important one, and the exact
method of how it takes place a detail. Harvey's experiments to demonstrate
that the blood passes from the arteries to the veins are so simply and
concisely stated that they may best be given in his own words.
"I have here to cite certain experiments," he wrote, "from which it seems
obvious that the blood enters a limb by the arteries, and returns from it by
the veins; that the arteries are the vessels carrying the blood from the heart,
and the veins the returning channels of the blood to the heart; that in the
limbs and extreme parts of the body the blood passes either by anastomosis
from the arteries into the veins, or immediately by the pores of the flesh, or
in both ways, as has already been said in speaking of the passage of the
blood through the lungs; whence it appears manifest that in the circuit the
blood moves from thence hither, and hence thither; from the centre to the
extremities, to wit, and from the extreme parts back again to the centre.
Finally, upon grounds of circulation, with the same elements as before, it
will be obvious that the quantity can neither be accounted for by the
ingesta, nor yet be held necessary to nutrition.
"Now let any one make an experiment on the arm of a man, either using
such a fillet as is employed in blood-letting or grasping the limb tightly with
his hand, the best subject for it being one who is lean, and who has large
veins, and the best time after exercise, when the body is warm, the pulse is
full, and the blood carried in large quantities to the extremities, for all then
is more conspicuous; under such circumstances let a ligature be thrown
about the extremity and drawn as tightly as can be borne: it will first be
perceived that beyond the ligature neither in the wrist nor anywhere else do

the arteries pulsate, that at the same time immediately above the ligature the
artery begins to rise higher at each diastole, to throb more violently, and to
swell in its vicinity with a kind of tide, as if it strove to break through and
overcome the obstacle to its current; the artery here, in short, appears as if it
were permanently full. The hand under such circumstances retains its
natural color and appearances; in the course of time it begins to fall
somewhat in temperature, indeed, but nothing is DRAWN into it.
"After the bandage has been kept on some short time in this way, let it be
slackened a little, brought to the state or term of middling tightness which is
used in bleeding, and it will be seen that the whole hand and arm will
instantly become deeply suffused and distended, injected, gorged with
blood, DRAWN, as it is said, by this middling ligature, without pain, or
heat, or any horror of a vacuum, or any other cause yet indicated.
"As we have noted, in connection with the tight ligature, that the artery
above the bandage was distended and pulsated, not below it, so, in the case
of the moderately tight bandage, on the contrary, do we find that the veins
below, never above, the fillet swell and become dilated, while the arteries
shrink; and such is the degree of distention of the veins here that it is only
very strong pressure that will force the blood beyond the fillet and cause
any of the veins in the upper part of the arm to rise.
"From these facts it is easy for any careful observer to learn that the
blood enters an extremity by the arteries; for when they are effectively
compressed nothing is DRAWN to the member; the hand preserves its
color; nothing flows into it, neither is it distended; but when the pressure is
diminished, as it is with the bleeding fillet, it is manifest that the blood is
instantly thrown in with force, for then the hand begins to swell; which is as
much as to say that when the arteries pulsate the blood is flowing through
them, as it is when the moderately tight ligature is applied; but when they
do not pulsate, or when a tight ligature is used, they cease from transmitting
anything; they are only distended above the part where the ligature is
applied. The veins again being compressed, nothing can flow through them;
the certain indication of which is that below the ligature they are much
more tumid than above it, and than they usually appear when there is no
bandage upon the arm.
"It therefore plainly appears that the ligature prevents the return of the
blood through the veins to the parts above it, and maintains those beneath it

in a state of permanent distention. But the arteries, in spite of the pressure,
and under the force and impulse of the heart, send on the blood from the
internal parts of the body to the parts beyond the bandage."(5)
This use of ligatures is very significant, because, as shown, a very tight
ligature stops circulation in both arteries and veins, while a loose one, while
checking the circulation in the veins, which lie nearer the surface and are
not so directly influenced by the force of the heart, does not stop the
passage of blood in the arteries, which are usually deeply imbedded in the
tissues, and not so easily influenced by pressure from without.
The last step of Harvey's demonstration was to prove that the blood does
flow along the veins to the heart, aided by the valves that had been the
cause of so much discussion and dispute between the great sixteenth-
century anatomists. Harvey not only demonstrated the presence of these
valves, but showed conclusively, by simple experiments, what their
function was, thus completing his demonstration of the phenomena of the
circulation.
The final ocular demonstration of the passage of the blood from the
arteries to the veins was not to be made until four years after Harvey's
death. This process, which can be observed easily in the web of a frog's foot
by the aid of a low-power lens, was first demonstrated by Marcello
Malpighi (1628-1694) in 1661. By the aid of a lens he first saw the small
"capillary" vessels connecting the veins and arteries in a piece of dried lung.
Taking his cue from this, he examined the lung of a turtle, and was able to
see in it the passage of the corpuscles through these minute vessels, making
their way along these previously unknown channels from the arteries into
the veins on their journey back to the heart. Thus the work of Harvey, all
but complete, was made absolutely entire by the great Italian. And all this in
a single generation.
LEEUWENHOEK DISCOVERS BACTERIA
The seventeenth century was not to close, however, without another
discovery in science, which, when applied to the causation of disease
almost two centuries later, revolutionized therapeutics more completely
than any one discovery. This was the discovery of microbes, by Antonius
von Leeuwenhoek (1632-1723), in 1683. Von Leeuwenhoek discovered that
"in the white matter between his teeth" there were millions of microscopic
"animals"—more, in fact, than "there were human beings in the united

Netherlands," and all "moving in the most delightful manner." There can be
no question that he saw them, for we can recognize in his descriptions of
these various forms of little "animals" the four principal forms of microbes
—the long and short rods of bacilli and bacteria, the spheres of micrococci,
and the corkscrew spirillum.
The presence of these microbes in his mouth greatly annoyed Antonius,
and he tried various methods of getting rid of them, such as using vinegar
and hot coffee. In doing this he little suspected that he was anticipating
modern antiseptic surgery by a century and three-quarters, and to be
attempting what antiseptic surgery is now able to accomplish. For the
fundamental principle of antisepsis is the use of medicines for ridding
wounds of similar microscopic organisms. Von Leenwenhoek was only
temporarily successful in his attempts, however, and took occasion to
communicate his discovery to the Royal Society of England, hoping that
they would be "interested in this novelty." Probably they were, but not
sufficiently so for any member to pursue any protracted investigations or
reach any satisfactory conclusions, and the whole matter was practically
forgotten until the middle of the nineteenth century.

VIII. MEDICINE IN THE SIXTEENTH AND
SEVENTEENTH CENTURIES
Of the half-dozen surgeons who were prominent in the sixteenth century,
Ambroise Pare (1517-1590), called the father of French surgery, is perhaps
the most widely known. He rose from the position of a common barber to
that of surgeon to three French monarchs, Henry II., Francis II., and Charles
IX. Some of his mottoes are still first principles of the medical man. Among
others are: "He who becomes a surgeon for the sake of money, and not for
the sake of knowledge, will accomplish nothing"; and "A tried remedy is
better than a newly invented." On his statue is his modest estimate of his
work in caring for the wounded, "Je le pansay, Dieu le guarit"—I dressed
him, God cured him.
It was in this dressing of wounds on the battlefield that he accidentally
discovered how useless and harmful was the terribly painful treatment of
applying boiling oil to gunshot wounds as advocated by John of Vigo. It
happened that after a certain battle, where there was an unusually large
number of casualties, Pare found, to his horror, that no more boiling oil was
available for the surgeons, and that he should be obliged to dress the
wounded by other simpler methods. To his amazement the results proved
entirely satisfactory, and from that day he discarded the hot-oil treatment.
As Pare did not understand Latin he wrote his treatises in French, thus
inaugurating a custom in France that was begun by Paracelsus in Germany
half a century before. He reintroduced the use of the ligature in controlling
hemorrhage, introduced the "figure of eight" suture in the operation for
hare-lip, improved many of the medico-legal doctrines, and advanced the
practice of surgery generally. He is credited with having successfully
performed the operation for strangulated hernia, but he probably borrowed
it from Peter Franco (1505-1570), who published an account of this
operation in 1556. As this operation is considered by some the most
important operation in surgery, its discoverer is entitled to more than
passing notice, although he was despised and ignored by the surgeons of his
time.

Franco was an illiterate travelling lithotomist—a class of itinerant
physicians who were very generally frowned down by the regular
practitioners of medicine. But Franco possessed such skill as an operator,
and appears to have been so earnest in the pursuit of what he considered a
legitimate calling, that he finally overcame the popular prejudice and
became one of the salaried surgeons of the republic of Bern. He was the
first surgeon to perform the suprapubic lithotomy operation—the removal
of stone through the abdomen instead of through the perineum. His works,
while written in an illiterate style, give the clearest descriptions of any of
the early modern writers.
As the fame of Franco rests upon his operation for prolonging human
life, so the fame of his Italian contemporary, Gaspar Tagliacozzi (1545-
1599), rests upon his operation for increasing human comfort and happiness
by restoring amputated noses. At the time in which he lived amputation of
the nose was very common, partly from disease, but also because a certain
pope had fixed the amputation of that member as the penalty for larceny.
Tagliacozzi probably borrowed his operation from the East; but he was the
first Western surgeon to perform it and describe it. So great was the fame of
his operations that patients flocked to him from all over Europe, and each
"went away with as many noses as he liked." Naturally, the man who
directed his efforts to restoring structures that bad been removed by order of
the Church was regarded in the light of a heretic by many theologians; and
though he succeeded in cheating the stake or dungeon, and died a natural
death, his body was finally cast out of the church in which it had been
buried.
In the sixteenth century Germany produced a surgeon, Fabricius Hildanes
(1560-1639), whose work compares favorably with that of Pare, and whose
name would undoubtedly have been much better known had not the
circumstances of the time in which he lived tended to obscure his merits.
The blind followers of Paracelsus could see nothing outside the pale of their
master's teachings, and the disastrous Thirty Years' War tended to obscure
and retard all scientific advances in Germany. Unlike many of his fellow-
surgeons, Hildanes was well versed in Latin and Greek; and, contrary to the
teachings of Paracelsus, he laid particular stress upon the necessity of the
surgeon having a thorough knowledge of anatomy. He had a helpmate in his
wife, who was also something of a surgeon, and she is credited with having
first made use of the magnet in removing particles of metal from the eye.

Hildanes tells of a certain man who had been injured by a small piece of
steel in the cornea, which resisted all his efforts to remove it. After
observing Hildanes' fruitless efforts for a time, it suddenly occurred to his
wife to attempt to make the extraction with a piece of loadstone. While the
physician held open the two lids, his wife attempted to withdraw the steel
with the magnet held close to the cornea, and after several efforts she was
successful—which Hildanes enumerates as one of the advantages of being a
married man.
Hildanes was particularly happy in his inventions of surgical instruments,
many of which were designed for locating and removing the various
missiles recently introduced in warfare.
The seventeenth century, which was such a flourishing one for anatomy
and physiology, was not as productive of great surgeons or advances in
surgery as the sixteenth had been or the eighteenth was to be. There was a
gradual improvement all along the line, however, and much of the work
begun by such surgeons as Pare and Hildanes was perfected or improved.
Perhaps the most progressive surgeon of the century was an Englishman,
Richard Wiseman (1625-1686), who, like Harvey, enjoyed royal favor,
being in the service of all the Stuart kings. He was the first surgeon to
advocate primary amputation, in gunshot wounds, of the limbs, and also to
introduce the treatment of aneurisms by compression; but he is generally
rated as a conservative operator, who favored medication rather than radical
operations, where possible.
In Italy, Marcus Aurelius Severinus (1580-1656) and Peter Marchettis
(1589-1675) were the leading surgeons of their nation. Like many of his
predecessors in Europe, Severinus ran amuck with the Holy Inquisition and
fled from Naples. But the waning of the powerful arm of the Church is
shown by the fact that he was brought back by the unanimous voice of the
grateful citizens, and lived in safety despite the frowns of the theologians.
The sixteenth century cannot be said to have added much of importance
in the field of practical medicine, and, as in the preceding and succeeding
centuries, was at best only struggling along in the wake of anatomy,
physiology, and surgery. In the seventeenth century, however, at least one
discovery in therapeutics was made that has been an inestimable boon to
humanity ever since. This was the introduction of cinchona bark (from
which quinine is obtained) in 1640. But this century was productive of

many medical SYSTEMS, and could boast of many great names among the
medical profession, and, on the whole, made considerably more progress
than the preceding century.
Of the founders of medical systems, one of the most widely known is Jan
Baptista van Helmont (1578-1644), an eccentric genius who constructed a
system of medicine of his own and for a time exerted considerable
influence. But in the end his system was destined to pass out of existence,
not very long after the death of its author. Van Helmont was not only a
physician, but was master of all the other branches of learning of the time,
taking up the study of medicine and chemistry as an after-thought, but
devoting himself to them with the greatest enthusiasm once he had begun
his investigations. His attitude towards existing doctrines was as
revolutionary as that of Paracelsus, and he rejected the teachings of Galen
and all the ancient writers, although retaining some of the views of
Paracelsus. He modified the archaeus of Paracelsus, and added many
complications to it. He believed the whole body to be controlled by an
archaeus influus, the soul by the archaei insiti, and these in turn controlled
by the central archeus. His system is too elaborate and complicated for full
explanation, but its chief service to medicine was in introducing new
chemical methods in the preparation of drugs. In this way he was indirectly
connected with the establishment of the Iatrochemical school. It was he
who first used the word "gas"—a word coined by him, along with many
others that soon fell into disuse.
The principles of the Iatrochemical school were the use of chemical
medicines, and a theory of pathology different from the prevailing
"humoral" pathology. The founder of this school was Sylvius (Franz de le
Boe, 1614-1672), professor of medicine at Leyden. He attempted to
establish a permanent system of medicine based on the newly discovered
theory of the circulation and the new chemistry, but his name is
remembered by medical men because of the fissure in the brain (fissure of
Sylvius) that bears it. He laid great stress on the cause of fevers and other
diseases as originating in the disturbances of the process of fermentation in
the stomach. The doctrines of Sylvius spread widely over the continent, but
were not generally accepted in England until modified by Thomas Willis
(1622-1675), whose name, like that of Sylvius, is perpetuated by a structure
in the brain named after him, the circle of Willis. Willis's descriptions of
certain nervous diseases, and an account of diabetes, are the first recorded,

and added materially to scientific medicine. These schools of medicine
lasted until the end of the seventeenth century, when they were finally
overthrown by Sydenham.
The Iatrophysical school (also called iatromathematical, iatromechanical,
or physiatric) was founded on theories of physiology, probably by Borelli,
of Naples (1608-1679), although Sanctorius; Sanctorius, a professor at
Padua, was a precursor, if not directly interested in establishing it.
Sanctorius discovered the fact that an "insensible perspiration" is being
given off by the body continually, and was amazed to find that loss of
weight in this way far exceeded the loss of weight by all other excretions of
the body combined. He made this discovery by means of a peculiar
weighing-machine to which a chair was attached, and in which he spent
most of his time. Very naturally he overestimated the importance of this
discovery, but it was, nevertheless, of great value in pointing out the
hygienic importance of the care of the skin. He also introduced a
thermometer which he advocated as valuable in cases of fever, but the
instrument was probably not his own invention, but borrowed from his
friend Galileo.
Harvey's discovery of the circulation of the blood laid the foundation of
the Iatrophysical school by showing that this vital process was comparable
to a hydraulic system. In his On the Motive of Animals, Borelli first
attempted to account for the phenomena of life and diseases on these
principles. The iatromechanics held that the great cause of disease is due to
different states of elasticity of the solids of the body interfering with the
movements of the fluids, which are themselves subject to changes in
density, one or both of these conditions continuing to cause stagnation or
congestion. The school thus founded by Borelli was the outcome of the
unbounded enthusiasm, with its accompanying exaggeration of certain
phenomena with the corresponding belittling of others that naturally follows
such a revolutionary discovery as that of Harvey. Having such a founder as
the brilliant Italian Borelli, it was given a sufficient impetus by his writings
to carry it some distance before it finally collapsed. Some of the
exaggerated mathematical calculations of Borelli himself are worth noting.
Each heart-beat, as he calculated it, overcomes a resistance equal to one
hundred and eighty thousand pounds;—the modern physiologist estimates
its force at from five to nine ounces!

THOMAS SYDENHAM
But while the Continent was struggling with these illusive "systems," and
dabbling in mystic theories that were to scarcely outlive the men who
conceived them, there appeared in England—the "land of common-sense,"
as a German scientist has called it—"a cool, clear, and unprejudiced spirit,"
who in the golden age of systems declined "to be like the man who builds
the chambers of the upper story of his house before he had laid securely the
foundation walls."(1) This man was Thomas Sydenham (1624-1689), who,
while the great Harvey was serving the king as surgeon, was fighting as a
captain in the parliamentary army. Sydenham took for his guide the
teachings of Hippocrates, modified to suit the advances that had been made
in scientific knowledge since the days of the great Greek, and established,
as a standard, observation and experience. He cared little for theory unless
confirmed by practice, but took the Hippocratic view that nature cured
diseases, assisted by the physician. He gave due credit, however, to the
importance of the part played by the assistant. As he saw it, medicine could
be advanced in three ways: (1) "By accurate descriptions or natural histories
of diseases; (2) by establishing a fixed principle or method of treatment,
founded upon experience; (3) by searching for specific remedies, which he
believes must exist in considerable numbers, though he admits that the only
one yet discovered is Peruvian bark."(2) As it happened, another equally
specific remedy, mercury, when used in certain diseases, was already
known to him, but he evidently did not recognize it as such.
The influence on future medicine of Sydenham's teachings was most
pronounced, due mostly to his teaching of careful observation. To most
physicians, however, he is now remembered chiefly for his introduction of
the use of laudanum, still considered one of the most valuable remedies of
modern pharmacopoeias. The German gives the honor of introducing this
preparation to Paracelsus, but the English-speaking world will always
believe that the credit should be given to Sydenham.

IX. PHILOSOPHER-SCIENTISTS AND NEW
INSTITUTIONS OF LEARNING
We saw that in the old Greek days there was no sharp line of demarcation
between the field of the philosopher and that of the scientist. In the
Hellenistic epoch, however, knowledge became more specialized, and our
recent chapters have shown us scientific investigators whose efforts were
far enough removed from the intangibilities of the philosopher. It must not
be overlooked, however, that even in the present epoch there were men
whose intellectual efforts were primarily directed towards the subtleties of
philosophy, yet who had also a penchant for strictly scientific imaginings, if
not indeed for practical scientific experiments. At least three of these men
were of sufficient importance in the history of the development of science
to demand more than passing notice. These three are the Englishman
Francis Bacon (1561-1626), the Frenchman Rene Descartes (1596-1650);
and the German Gottfried Leibnitz (1646-1716). Bacon, as the earliest path-
breaker, showed the way, theoretically at least, in which the sciences should
be studied; Descartes, pursuing the methods pointed out by Bacon, carried
the same line of abstract reason into practice as well; while Leibnitz,
coming some years later, and having the advantage of the wisdom of his
two great predecessors, was naturally influenced by both in his views of
abstract scientific principles.
Bacon's career as a statesman and his faults and misfortunes as a man do
not concern us here. Our interest in him begins with his entrance into
Trinity College, Cambridge, where he took up the study of all the sciences
taught there at that time. During the three years he became more and more
convinced that science was not being studied in a profitable manner, until at
last, at the end of his college course, he made ready to renounce the old
Aristotelian methods of study and advance his theory of inductive study.
For although he was a great admirer of Aristotle's work, he became
convinced that his methods of approaching study were entirely wrong.
"The opinion of Aristotle," he says, in his De Argumentum Scientiarum,
"seemeth to me a negligent opinion, that of those things which exist by

nature nothing can be changed by custom; using for example, that if a stone
be thrown ten thousand times up it will not learn to ascend; and that by
often seeing or hearing we do not learn to see or hear better. For though this
principle be true in things wherein nature is peremptory (the reason whereof
we cannot now stand to discuss), yet it is otherwise in things wherein nature
admitteth a latitude. For he might see that a straight glove will come more
easily on with use; and that a wand will by use bend otherwise than it grew;
and that by use of the voice we speak louder and stronger; and that by use
of enduring heat or cold we endure it the better, and the like; which latter
sort have a nearer resemblance unto that subject of manners he handleth
than those instances which he allegeth."(1)
These were his opinions, formed while a young man in college, repeated
at intervals through his maturer years, and reiterated and emphasized in his
old age. Masses of facts were to be obtained by observing nature at first
hand, and from such accumulations of facts deductions were to be made. In
short, reasoning was to be from the specific to the general, and not vice
versa.
It was by his teachings alone that Bacon thus contributed to the
foundation of modern science; and, while he was constantly thinking and
writing on scientific subjects, he contributed little in the way of actual
discoveries. "I only sound the clarion," he said, "but I enter not the battle."
The case of Descartes, however, is different. He both sounded the clarion
and entered into the fight. He himself freely acknowledges his debt to
Bacon for his teachings of inductive methods of study, but modern criticism
places his work on the same plane as that of the great Englishman. "If you
lay hold of any characteristic product of modern ways of thinking," says
Huxley, "either in the region of philosophy or in that of science, you find
the spirit of that thought, if not its form, has been present in the mind of the
great Frenchman."(2)
Descartes, the son of a noble family of France, was educated by Jesuit
teachers. Like Bacon, he very early conceived the idea that the methods of
teaching and studying science were wrong, but be pondered the matter well
into middle life before putting into writing his ideas of philosophy and
science. Then, in his Discourse Touching the Method of Using One's
Reason Rightly and of Seeking Scientific Truth, he pointed out the way of
seeking after truth. His central idea in this was to emphasize the importance

of DOUBT, and avoidance of accepting as truth anything that does not
admit of absolute and unqualified proof. In reaching these conclusions he
had before him the striking examples of scientific deductions by Galileo,
and more recently the discovery of the circulation of the blood by Harvey.
This last came as a revelation to scientists, reducing this seemingly occult
process, as it did, to the field of mechanical phenomena. The same
mechanical laws that governed the heavenly bodies, as shown by Galileo,
governed the action of the human heart, and, for aught any one knew, every
part of the body, and even the mind itself.
Having once conceived this idea, Descartes began a series of dissections
and experiments upon the lower animals, to find, if possible, further proof
of this general law. To him the human body was simply a machine, a
complicated mechanism, whose functions were controlled just as any other
piece of machinery. He compared the human body to complicated
machinery run by water-falls and complicated pipes. "The nerves of the
machine which I am describing," he says, "may very well be compared to
the pipes of these waterworks; its muscles and its tendons to the other
various engines and springs which seem to move them; its animal spirits to
the water which impels them, of which the heart is the fountain; while the
cavities of the brain are the central office. Moreover, respiration and other
such actions as are natural and usual in the body, and which depend on the
course of the spirits, are like the movements of a clock, or a mill, which
may be kept up by the ordinary flow of water."(3)
In such passages as these Descartes anticipates the ideas of physiology of
the present time. He believed that the functions are performed by the
various organs of the bodies of animals and men as a mechanism, to which
in man was added the soul. This soul he located in the pineal gland, a
degenerate and presumably functionless little organ in the brain. For years
Descartes's idea of the function of this gland was held by many
physiologists, and it was only the introduction of modern high-power
microscopy that reduced this also to a mere mechanism, and showed that it
is apparently the remains of a Cyclopean eye once common to man's remote
ancestors.
Descartes was the originator of a theory of the movements of the
universe by a mechanical process—the Cartesian theory of vortices—which
for several decades after its promulgation reigned supreme in science. It is

the ingenuity of this theory, not the truth of its assertions, that still excites
admiration, for it has long since been supplanted. It was certainly the best
hitherto advanced—the best "that the observations of the age admitted,"
according to D'Alembert.
According to this theory the infinite universe is full of matter, there being
no such thing as a vacuum. Matter, as Descartes believed, is uniform in
character throughout the entire universe, and since motion cannot take place
in any part of a space completely filled, without simultaneous movement in
all other parts, there are constant more or less circular movements, vortices,
or whirlpools of particles, varying, of course, in size and velocity. As a
result of this circular movement the particles of matter tend to become
globular from contact with one another. Two species of matter are thus
formed, one larger and globular, which continue their circular motion with a
constant tendency to fly from the centre of the axis of rotation, the other
composed of the clippings resulting from the grinding process. These
smaller "filings" from the main bodies, becoming smaller and smaller,
gradually lose their velocity and accumulate in the centre of the vortex. This
collection of the smaller matter in the centre of the vortex constitutes the
sun or star, while the spherical particles propelled in straight lines from the
centre towards the circumference of the vortex produce the phenomenon of
light radiating from the central star. Thus this matter becomes the
atmosphere revolving around the accumulation at the centre. But the small
particles being constantly worn away from the revolving spherical particles
in the vortex, become entangled in their passage, and when they reach the
edge of the inner strata of solar dust they settle upon it and form what we
call sun-spots. These are constantly dissolved and reformed, until
sometimes they form a crust round the central nucleus.
As the expansive force of the star diminishes in the course of time, it is
encroached upon by neighboring vortices. If the part of the encroaching star
be of a less velocity than the star which it has swept up, it will presently
lose its hold, and the smaller star pass out of range, becoming a comet. But
if the velocity of the vortex into which the incrusted star settles be
equivalent to that of the surrounded vortex, it will hold it as a captive, still
revolving and "wrapt in its own firmament." Thus the several planets of our
solar system have been captured and held by the sun-vortex, as have the
moon and other satellites.

But although these new theories at first created great enthusiasm among
all classes of philosophers and scientists, they soon came under the ban of
the Church. While no actual harm came to Descartes himself, his writings
were condemned by the Catholic and Protestant churches alike. The spirit of
philosophical inquiry he had engendered, however, lived on, and is largely
responsible for modern philosophy.
In many ways the life and works of Leibnitz remind us of Bacon rather
than Descartes. His life was spent in filling high political positions, and his
philosophical and scientific writings were by-paths of his fertile mind. He
was a theoretical rather than a practical scientist, his contributions to
science being in the nature of philosophical reasonings rather than practical
demonstrations. Had he been able to withdraw from public life and devote
himself to science alone, as Descartes did, he would undoubtedly have
proved himself equally great as a practical worker. But during the time of
his greatest activity in philosophical fields, between the years 1690 and
1716, he was all the time performing extraordinary active duties in entirely
foreign fields. His work may be regarded, perhaps, as doing for Germany in
particular what Bacon's did for England and the rest of the world in general.
Only a comparatively small part of his philosophical writings concern us
here. According to his theory of the ultimate elements of the universe, the
entire universe is composed of individual centres, or monads. To these
monads he ascribed numberless qualities by which every phase of nature
may be accounted. They were supposed by him to be percipient, self-acting
beings, not under arbitrary control of the deity, and yet God himself was the
original monad from which all the rest are generated. With this conception
as a basis, Leibnitz deduced his doctrine of pre-established harmony,
whereby the numerous independent substances composing the world are
made to form one universe. He believed that by virtue of an inward energy
monads develop themselves spontaneously, each being independent of
every other. In short, each monad is a kind of deity in itself—a microcosm
representing all the great features of the macrocosm.
It would be impossible clearly to estimate the precise value of the
stimulative influence of these philosophers upon the scientific thought of
their time. There was one way, however, in which their influence was made
very tangible—namely, in the incentive they gave to the foundation of
scientific societies.

SCIENTIFIC SOCIETIES
At the present time, when the elements of time and distance are
practically eliminated in the propagation of news, and when cheap printing
has minimized the difficulties of publishing scientific discoveries, it is
difficult to understand the isolated position of the scientific investigation of
the ages that preceded steam and electricity. Shut off from the world and
completely out of touch with fellow-laborers perhaps only a few miles
away, the investigators were naturally seriously handicapped; and
inventions and discoveries were not made with the same rapidity that they
would undoubtedly have been had the same men been receiving daily,
weekly, or monthly communications from fellow-laborers all over the
world, as they do to-day. Neither did they have the advantage of public or
semi-public laboratories, where they were brought into contact with other
men, from whom to gather fresh trains of thought and receive the stimulus
of their successes or failures. In the natural course of events, however,
neighbors who were interested in somewhat similar pursuits, not of the
character of the rivalry of trade or commerce, would meet more or less
frequently and discuss their progress. The mutual advantages of such
intercourse would be at once appreciated; and it would be but a short step
from the casual meeting of two neighborly scientists to the establishment of
"societies," meeting at fixed times, and composed of members living within
reasonable travelling distance. There would, perhaps, be the weekly or
monthly meetings of men in a limited area; and as the natural outgrowth of
these little local societies, with frequent meetings, would come the
formation of larger societies, meeting less often, where members travelled a
considerable distance to attend. And, finally, with increased facilities for
communication and travel, the great international societies of to-day would
be produced—the natural outcome of the neighborly meetings of the
primitive mediaeval investigators.
In Italy, at about the time of Galileo, several small societies were formed.
One of the most important of these was the Lyncean Society, founded about
the year 1611, Galileo himself being a member. This society was succeeded
by the Accademia del Cimento, at Florence, in 1657, which for a time
flourished, with such a famous scientist as Torricelli as one of its members.
In England an impetus seems to have been given by Sir Francis Bacon's
writings in criticism and censure of the system of teaching in colleges. It is

supposed that his suggestions as to what should be the aims of a scientific
society led eventually to the establishment of the Royal Society. He pointed
out how little had really been accomplished by the existing institutions of
learning in advancing science, and asserted that little good could ever come
from them while their methods of teaching remained unchanged. He
contended that the system which made the lectures and exercises of such a
nature that no deviation from the established routine could be thought of
was pernicious. But he showed that if any teacher had the temerity to turn
from the traditional paths, the daring pioneer was likely to find
insurmountable obstacles placed in the way of his advancement. The studies
were "imprisoned" within the limits of a certain set of authors, and
originality in thought or teaching was to be neither contemplated nor
tolerated.
The words of Bacon, given in strong and unsparing terms of censure and
condemnation, but nevertheless with perfect justification, soon bore fruit.
As early as the year 1645 a small company of scientists had been in the
habit of meeting at some place in London to discuss philosophical and
scientific subjects for mental advancement. In 1648, owing to the political
disturbances of the time, some of the members of these meetings removed
to Oxford, among them Boyle, Wallis, and Wren, where the meetings were
continued, as were also the meetings of those left in London. In 1662,
however, when the political situation bad become more settled, these two
bodies of men were united under a charter from Charles II., and Bacon's
ideas were practically expressed in that learned body, the Royal Society of
London. And it matters little that in some respects Bacon's views were not
followed in the practical workings of the society, or that the division of
labor in the early stages was somewhat different than at present. The aim of
the society has always been one for the advancement of learning; and if
Bacon himself could look over its records, he would surely have little fault
to find with the aid it has given in carrying out his ideas for the
promulgation of useful knowledge.
Ten years after the charter was granted to the Royal Society of London,
Lord Bacon's words took practical effect in Germany, with the result that
the Academia Naturae Curiosorum was founded, under the leadership of
Professor J. C. Sturm. The early labors of this society were devoted to a
repetition of the most notable experiments of the time, and the work of the
embryo society was published in two volumes, in 1672 and 1685

respectively, which were practically text-books of the physics of the period.
It was not until 1700 that Frederick I. founded the Royal Academy of
Sciences at Berlin, after the elaborate plan of Leibnitz, who was himself the
first president.
Perhaps the nearest realization of Bacon's ideal, however, is in the Royal
Academy of Sciences at Paris, which was founded in 1666 under the
administration of Colbert, during the reign of Louis XIV. This institution
not only recognized independent members, but had besides twenty
pensionnaires who received salaries from the government. In this way a
select body of scientists were enabled to pursue their investigations without
being obliged to "give thought to the morrow" for their sustenance. In
return they were to furnish the meetings with scientific memoirs, and once a
year give an account of the work they were engaged upon. Thus a certain
number of the brightest minds were encouraged to devote their entire time
to scientific research, "delivered alike from the temptations of wealth or the
embarrassments of poverty." That such a plan works well is amply attested
by the results emanating from the French academy. Pensionnaires in various
branches of science, however, either paid by the state or by learned
societies, are no longer confined to France.
Among the other early scientific societies was the Imperial Academy of
Sciences at St. Petersburg, projected by Peter the Great, and established by
his widow, Catharine I., in 1725; and also the Royal Swedish Academy,
incorporated in 1781, and counting among its early members such men as
the celebrated Linnaeus. But after the first impulse had resulted in a few
learned societies, their manifest advantage was so evident that additional
numbers increased rapidly, until at present almost every branch of every
science is represented by more or less important bodies; and these are,
individually and collectively, adding to knowledge and stimulating interest
in the many fields of science, thus vindicating Lord Bacon's asseverations
that knowledge could be satisfactorily promulgated in this manner.

X. THE SUCCESSORS OF GALILEO IN
PHYSICAL SCIENCE
We have now to witness the diversified efforts of a company of men who,
working for the most part independently, greatly added to the data of the
physical sciences—such men as Boyle, Huygens, Von Gericke, and Hooke.
It will be found that the studies of these men covered the whole field of
physical sciences as then understood—the field of so-called natural
philosophy. We shall best treat these successors of Galileo and precursors of
Newton somewhat biographically, pointing out the correspondences and
differences between their various accomplishments as we proceed. It will be
noted in due course that the work of some of them was anticipatory of great
achievements of a later century.
ROBERT BOYLE (1627-1691)
Some of Robert Boyle's views as to the possible structure of atmospheric
air will be considered a little farther on in this chapter, but for the moment
we will take up the consideration of some of his experiments upon that as
well as other gases. Boyle was always much interested in alchemy, and
carried on extensive experiments in attempting to accomplish the
transmutation of metals; but he did not confine himself to these
experiments, devoting himself to researches in all the fields of natural
philosophy. He was associated at Oxford with a company of scientists,
including Wallis and Wren, who held meetings and made experiments
together, these gatherings being the beginning, as mentioned a moment ago,
of what finally became the Royal Society. It was during this residence at
Oxford that many of his valuable researches upon air were made, and
during this time be invented his air-pump, now exhibited in the Royal
Society rooms at Burlington House.(1)
His experiments to prove the atmospheric pressure are most interesting
and conclusive. "Having three small, round glass bubbles, blown at the
flame of a lamp, about the size of hazel-nuts," he says, "each of them with a
short, slender stem, by means whereof they were so exactly poised in water
that a very small change of weight would make them either emerge or sink;

at a time when the atmosphere was of convenient weight, I put them into a
wide-mouthed glass of common water, and leaving them in a quiet place,
where they were frequently in my eye, I observed that sometimes they
would be at the top of the water, and remain there for several days, or
perhaps weeks, together, and sometimes fall to the bottom, and after having
continued there for some time rise again. And sometimes they would rise or
fall as the air was hot or cold."(2)
It was in the course of these experiments that the observations made by
Boyle led to the invention of his "statical barometer," the mercurial
barometer having been invented, as we have seen, by Torricelli, in 1643. In
describing this invention he says: "Making choice of a large, thin, and light
glass bubble, blown at the flame of a lamp, I counterpoised it with a
metallic weight, in a pair of scales that were suspended in a frame, that
would turn with the thirtieth part of a grain. Both the frame and the balance
were then placed near a good barometer, whence I might learn the present
weight of the atmosphere; when, though the scales were unable to show all
the variations that appeared in the mercurial barometer, yet they gave notice
of those that altered the height of the mercury half a quarter of an inch."(3)
A fairly sensitive barometer, after all. This statical barometer suggested
several useful applications to the fertile imagination of its inventor, among
others the measuring of mountain-peaks, as with the mercurial barometer,
the rarefication of the air at the top giving a definite ratio to the more
condensed air in the valley.
Another of his experiments was made to discover the atmospheric
pressure to the square inch. After considerable difficulty he determined that
the relative weight of a cubic inch of water and mercury was about one to
fourteen, and computing from other known weights he determined that
"when a column of quicksilver thirty inches high is sustained in the
barometer, as it frequently happens, a column of air that presses upon an
inch square near the surface of the earth must weigh about fifteen
avoirdupois pounds."(4) As the pressure of air at the sea-level is now
estimated at 14.7304 pounds to the square inch, it will be seen that Boyle's
calculation was not far wrong.
From his numerous experiments upon the air, Boyle was led to believe
that there were many "latent qualities" due to substances contained in it that
science had as yet been unable to fathom, believing that there is "not a more

heterogeneous body in the world." He believed that contagious diseases
were carried by the air, and suggested that eruptions of the earth, such as
those made by earthquakes, might send up "venomous exhalations" that
produced diseases. He suggested also that the air might play an important
part in some processes of calcination, which, as we shall see, was proved to
be true by Lavoisier late in the eighteenth century. Boyle's notions of the
exact chemical action in these phenomena were of course vague and
indefinite, but he had observed that some part was played by the air, and he
was right in supposing that the air "may have a great share in varying the
salts obtainable from calcined vitriol."(5)
Although he was himself such a painstaking observer of facts, he had the
fault of his age of placing too much faith in hear-say evidence of untrained
observers. Thus, from the numerous stories he heard concerning the growth
of metals in previously exhausted mines, he believed that the air was
responsible for producing this growth—in which he undoubtedly believed.
The story of a tin-miner that, in his own time, after a lapse of only twenty-
five years, a heap, of earth previously exhausted of its ore became again
even more richly impregnated than before by lying exposed to the air,
seems to have been believed by the philosopher.
As Boyle was an alchemist, and undoubtedly believed in the alchemic
theory that metals have "spirits" and various other qualities that do not
exist, it is not surprising that he was credulous in the matter of beliefs
concerning peculiar phenomena exhibited by them. Furthermore, he
undoubtedly fell into the error common to "specialists," or persons working
for long periods of time on one subject—the error of over-enthusiasm in his
subject. He had discovered so many remarkable qualities in the air that it is
not surprising to find that he attributed to it many more that he could not
demonstrate.
Boyle's work upon colors, although probably of less importance than his
experiments and deductions upon air, show that he was in the van as far as
the science of his day was concerned. As he points out, the schools of his
time generally taught that "color is a penetrating quality, reaching to the
innermost part of the substance," and, as an example of this, sealing-wax
was cited, which could be broken into minute bits, each particle retaining
the same color as its fellows or the original mass. To refute this theory, and
to show instances to the contrary, Boyle, among other things, shows that

various colors—blue, red, yellow—may be produced upon tempered steel,
and yet the metal within "a hair's-breadth of its surface" have none of these
colors. Therefore, he was led to believe that color, in opaque bodies at least,
is superficial.
"But before we descend to a more particular consideration of our
subject," he says, "'tis proper to observe that colors may be regarded either
as a quality residing in bodies to modify light after a particular manner, or
else as light itself so modified as to strike upon the organs of sight, and
cause the sensation we call color; and that this latter is the more proper
acceptation of the word color will appear hereafter. And indeed it is the
light itself, which after a certain manner, either mixed with shades or other-
wise, strikes our eyes and immediately produces that motion in the organ
which gives us the color of an object."(6)
In examining smooth and rough surfaces to determine the cause of their
color, he made use of the microscope, and pointed out the very obvious
example of the difference in color of a rough and a polished piece of the
same block of stone. He used some striking illustrations of the effect of
light and the position of the eye upon colors. "Thus the color of plush or
velvet will appear various if you stroke part of it one way and part another,
the posture of the particular threads in regard to the light, or the eye, being
thereby varied. And 'tis observable that in a field of ripe corn, blown upon
by the wind, there will appear waves of a color different from that of the
rest of the corn, because the wind, by depressing some of the ears more than
others, causes one to reflect more light from the lateral and strawy parts
than another."(7) His work upon color, however, as upon light, was entirely
overshadowed by the work of his great fellow-countryman Newton.
Boyle's work on electricity was a continuation of Gilbert's, to which he
added several new facts. He added several substances to Gilbert's list of
"electrics," experimented on smooth and rough surfaces in exciting of
electricity, and made the important discovery that amber retained its
attractive virtue after the friction that excited it bad ceased. "For the attrition
having caused an intestine motion in its parts," he says, "the heat thereby
excited ought not to cease as soon as ever the rubbing is over, but to
continue capable of emitting effluvia for some time afterwards, longer or
shorter according to the goodness of the electric and the degree of the
commotion made; all which, joined together, may sometimes make the

effect considerable; and by this means, on a warm day, I, with a certain
body not bigger than a pea, but very vigorously attractive, moved a steel
needle, freely poised, about three minutes after I had left off rubbing it."(8)
MARIOTTE AND VON GUERICKE
Working contemporaneously with Boyle, and a man whose name is
usually associated with his as the propounder of the law of density of gases,
was Edme Mariotte (died 1684), a native of Burgundy. Mariotte
demonstrated that but for the resistance of the atmosphere, all bodies,
whether light or heavy, dense or thin, would fall with equal rapidity, and he
proved this by the well-known "guinea-and-feather" experiment. Having
exhausted the air from a long glass tube in which a guinea piece and a
feather had been placed, he showed that in the vacuum thus formed they fell
with equal rapidity as often as the tube was reversed. From his various
experiments as to the pressure of the atmosphere he deduced the law that
the density and elasticity of the atmosphere are precisely proportional to the
compressing force (the law of Boyle and Mariotte). He also ascertained that
air existed in a state of mechanical mixture with liquids, "existing between
their particles in a state of condensation." He made many other
experiments, especially on the collision of bodies, but his most important
work was upon the atmosphere.
But meanwhile another contemporary of Boyle and Mariotte was
interesting himself in the study of the atmosphere, and had made a
wonderful invention and a most striking demonstration. This was Otto von
Guericke (1602-1686), Burgomaster of Magdeburg, and councillor to his
"most serene and potent Highness" the elector of that place. When not
engrossed with the duties of public office, he devoted his time to the study
of the sciences, particularly pneumatics and electricity, both then in their
infancy. The discoveries of Galileo, Pascal, and Torricelli incited him to
solve the problem of the creation of a vacuum—a desideratum since before
the days of Aristotle. His first experiments were with a wooden pump and a
barrel of water, but he soon found that with such porous material as wood a
vacuum could not be created or maintained. He therefore made use of a
globe of copper, with pump and stop-cock; and with this he was able to
pump out air almost as easily as water. Thus, in 1650, the air-pump was
invented. Continuing his experiments upon vacuums and atmospheric

pressure with his newly discovered pump, he made some startling
discoveries as to the enormous pressure exerted by the air.
It was not his intention, however, to demonstrate his newly acquired
knowledge by words or theories alone, nor by mere laboratory experiments;
but he chose instead an open field, to which were invited Emperor
Ferdinand III., and all the princes of the Diet at Ratisbon. When they were
assembled he produced two hollow brass hemispheres about two feet in
diameter, and placing their exactly fitting surfaces together, proceeded to
pump out the air from their hollow interior, thus causing them to stick
together firmly in a most remarkable way, apparently without anything
holding them. This of itself was strange enough; but now the worthy
burgomaster produced teams of horses, and harnessing them to either side
of the hemispheres, attempted to pull the adhering brasses apart. Five, ten,
fifteen teams—thirty horses, in all—were attached; but pull and tug as they
would they could not separate the firmly clasped hemispheres. The
enormous pressure of the atmosphere had been most strikingly
demonstrated.
But it is one thing to demonstrate, another to convince; and many of the
good people of Magdeburg shook their heads over this "devil's
contrivance," and predicted that Heaven would punish the Herr
Burgomaster, as indeed it had once by striking his house with lightning and
injuring some of his infernal contrivances. They predicted his future
punishment, but they did not molest him, for to his fellow-citizens, who
talked and laughed, drank and smoked with him, and knew him for the
honest citizen that he was, he did not seem bewitched at all. And so he lived
and worked and added other facts to science, and his brass hemispheres
were not destroyed by fanatical Inquisitors, but are still preserved in the
royal library at Berlin.
In his experiments with his air-pump he discovered many things
regarding the action of gases, among others, that animals cannot live in a
vacuum. He invented the anemoscope and the air-balance, and being thus
enabled to weight the air and note the changes that preceded storms and
calms, he was able still further to dumfound his wondering fellow-Magde-
burgers by more or less accurate predictions about the weather.
Von Guericke did not accept Gilbert's theory that the earth was a great
magnet, but in his experiments along lines similar to those pursued by

Gilbert, he not only invented the first electrical machine, but discovered
electrical attraction and repulsion. The electrical machine which he invented
consisted of a sphere of sulphur mounted on an iron axis to imitate the
rotation of the earth, and which, when rubbed, manifested electrical
reactions. When this globe was revolved and stroked with the dry hand it
was found that it attached to it "all sorts of little fragments, like leaves of
gold, silver, paper, etc." "Thus this globe," he says, "when brought rather
near drops of water causes them to swell and puff up. It likewise attracts air,
smoke, etc."(9) Before the time of Guericke's demonstrations, Cabaeus had
noted that chaff leaped back from an "electric," but he did not interpret the
phenomenon as electrical repulsion. Von Guericke, however, recognized it
as such, and refers to it as what he calls "expulsive virtue." "Even expulsive
virtue is seen in this globe," he says, "for it not only attracts, but also
REPELS again from itself little bodies of this sort, nor does it receive them
until they have touched something else." It will be observed from this that
he was very close to discovering the discharge of the electrification of
attracted bodies by contact with some other object, after which they are
reattracted by the electric.
He performed a most interesting experiment with his sulphur globe and a
feather, and in doing so came near anticipating Benjamin Franklin in his
discovery of the effects of pointed conductors in drawing off the discharge.
Having revolved and stroked his globe until it repelled a bit of down, he
removed the globe from its rack and advancing it towards the now repellent
down, drove it before him about the room. In this chase he observed that the
down preferred to alight against "the points of any object whatsoever." He
noticed that should the down chance to be driven within a few inches of a
lighted candle, its attitude towards the globe suddenly changed, and instead
of running away from it, it now "flew to it for protection"—the charge on
the down having been dissipated by the hot air. He also noted that if one
face of a feather had been first attracted and then repelled by the sulphur
ball, that the surface so affected was always turned towards the globe; so
that if the positions of the two were reversed, the sides of the feather
reversed also.
Still another important discovery, that of electrical conduction, was made
by Von Guericke. Until his discovery no one had observed the transference
of electricity from one body to another, although Gilbert had some time
before noted that a rod rendered magnetic at one end became so at the other.

Von Guericke's experiments were made upon a linen thread with his sulphur
globe, which, he says, "having been previously excited by rubbing, can
exercise likewise its virtue through a linen thread an ell or more long, and
there attract something." But this discovery, and his equally important one
that the sulphur ball becomes luminous when rubbed, were practically
forgotten until again brought to notice by the discoveries of Francis
Hauksbee and Stephen Gray early in the eighteenth century. From this we
may gather that Von Guericke himself did not realize the import of his
discoveries, for otherwise he would certainly have carried his investigations
still further. But as it was he turned his attention to other fields of research.
ROBERT HOOKE
A slender, crooked, shrivelled-limbed, cantankerous little man, with
dishevelled hair and haggard countenance, bad-tempered and irritable,
penurious and dishonest, at least in his claims for priority in discoveries—
this is the picture usually drawn, alike by friends and enemies, of Robert
Hooke (1635-1703), a man with an almost unparalleled genius for scientific
discoveries in almost all branches of science. History gives few examples
so striking of a man whose really great achievements in science would
alone have made his name immortal, and yet who had the pusillanimous
spirit of a charlatan—an almost insane mania, as it seems—for claiming the
credit of discoveries made by others. This attitude of mind can hardly be
explained except as a mania: it is certainly more charitable so to regard it.
For his own discoveries and inventions were so numerous that a few more
or less would hardly have added to his fame, as his reputation as a
philosopher was well established. Admiration for his ability and his
philosophical knowledge must always be marred by the recollection of his
arrogant claims to the discoveries of other philosophers.
It seems pretty definitely determined that Hooke should be credited with
the invention of the balance-spring for regulating watches; but for a long
time a heated controversy was waged between Hooke and Huygens as to
who was the real inventor. It appears that Hooke conceived the idea of the
balance-spring, while to Huygens belongs the credit of having adapted the
COILED spring in a working model. He thus made practical Hooke's
conception, which is without value except as applied by the coiled spring;
but, nevertheless, the inventor, as well as the perfector, should receive

credit. In this controversy, unlike many others, the blame cannot be laid at
Hooke's door.
Hooke was the first curator of the Royal Society, and when anything was
to be investigated, usually invented the mechanical devices for doing so.
Astronomical apparatus, instruments for measuring specific weights, clocks
and chronometers, methods of measuring the velocity of falling bodies,
freezing and boiling points, strength of gunpowder, magnetic instruments—
in short, all kinds of ingenious mechanical devices in all branches of
science and mechanics. It was he who made the famous air-pump of Robert
Boyle, based on Boyle's plans. Incidentally, Hooke claimed to be the
inventor of the first air-pump himself, although this claim is now entirely
discredited.
Within a period of two years he devised no less than thirty different
methods of flying, all of which, of course, came to nothing, but go to show
the fertile imagination of the man, and his tireless energy. He experimented
with electricity and made some novel suggestions upon the difference
between the electric spark and the glow, although on the whole his
contributions in this field are unimportant. He also first pointed out that the
motions of the heavenly bodies must be looked upon as a mechanical
problem, and was almost within grasping distance of the exact theory of
gravitation, himself originating the idea of making use of the pendulum in
measuring gravity. Likewise, he first proposed the wave theory of light;
although it was Huygens who established it on its present foundation.
Hooke published, among other things, a book of plates and descriptions
of his Microscopical Observations, which gives an idea of the advance that
had already been made in microscopy in his time. Two of these plates are
given here, which, even in this age of microscopy, are both interesting and
instructive. These plates are made from prints of Hooke's original copper
plates, and show that excellent lenses were made even at that time. They
illustrate, also, how much might have been accomplished in the field of
medicine if more attention had been given to microscopy by physicians.
Even a century later, had physicians made better use of their microscopes,
they could hardly have overlooked such an easily found parasite as the itch
mite, which is quite as easily detected as the cheese mite, pictured in
Hooke's book.

In justice to Hooke, and in extenuation of his otherwise inexcusable
peculiarities of mind, it should be remembered that for many years he
suffered from a painful and wasting disease. This may have affected his
mental equilibrium, without appreciably affecting his ingenuity. In his own
time this condition would hardly have been considered a disease; but to-
day, with our advanced ideas as to mental diseases, we should be more
inclined to ascribe his unfortunate attitude of mind to a pathological
condition, rather than to any manifestation of normal mentality. From this
point of view his mental deformity seems not unlike that of Cavendish's,
later, except that in the case of Cavendish it manifested itself as an
abnormal sensitiveness instead of an abnormal irritability.
CHRISTIAN HUYGENS
If for nothing else, the world is indebted to the man who invented the
pendulum clock, Christian Huygens (1629-1695), of the Hague, inventor,
mathematician, mechanician, astronomer, and physicist. Huygens was the
descendant of a noble and distinguished family, his father, Sir Constantine
Huygens, being a well-known poet and diplomatist. Early in life young
Huygens began his career in the legal profession, completing his education
in the juridical school at Breda; but his taste for mathematics soon led him
to neglect his legal studies, and his aptitude for scientific researches was so
marked that Descartes predicted great things of him even while he was a
mere tyro in the field of scientific investigation.
One of his first endeavors in science was to attempt an improvement of
the telescope. Reflecting upon the process of making lenses then in vogue,
young Huygens and his brother Constantine attempted a new method of
grinding and polishing, whereby they overcame a great deal of the spherical
and chromatic aberration. With this new telescope a much clearer field of
vision was obtained, so much so that Huygens was able to detect, among
other things, a hitherto unknown satellite of Saturn. It was these
astronomical researches that led him to apply the pendulum to regulate the
movements of clocks. The need for some more exact method of measuring
time in his observations of the stars was keenly felt by the young
astronomer, and after several experiments along different lines, Huygens hit
upon the use of a swinging weight; and in 1656 made his invention of the
pendulum clock. The year following, his clock was presented to the states-
general. Accuracy as to time is absolutely essential in astronomy, but until

the invention of Huygens's clock there was no precise, nor even
approximately precise, means of measuring short intervals.
Huygens was one of the first to adapt the micrometer to the telescope—a
mechanical device on which all the nice determination of minute distances
depends. He also took up the controversy against Hooke as to the
superiority of telescopic over plain sights to quadrants, Hooke contending
in favor of the plain. In this controversy, the subject of which attracted wide
attention, Huygens was completely victorious; and Hooke, being unable to
refute Huygens's arguments, exhibited such irritability that he increased his
already general unpopularity. All of the arguments for and against the
telescope sight are too numerous to be given here. In contending in its favor
Huygens pointed out that the unaided eye is unable to appreciate an angular
space in the sky less than about thirty seconds. Even in the best quadrant
with a plain sight, therefore, the altitude must be uncertain by that quantity.
If in place of the plain sight a telescope is substituted, even if it magnify
only thirty times, it will enable the observer to fix the position to one
second, with progressively increased accuracy as the magnifying power of
the telescope is increased. This was only one of the many telling arguments
advanced by Huygens.
In the field of optics, also, Huygens has added considerably to science,
and his work, Dioptrics, is said to have been a favorite book with Newton.
During the later part of his life, however, Huygens again devoted himself to
inventing and constructing telescopes, grinding the lenses, and devising, if
not actually making, the frame for holding them. These telescopes were of
enormous lengths, three of his object-glasses, now in possession of the
Royal Society, being of 123, 180, and 210 feet focal length respectively.
Such instruments, if constructed in the ordinary form of the long tube, were
very unmanageable, and to obviate this Huygens adopted the plan of
dispensing with the tube altogether, mounting his lenses on long poles
manipulated by machinery. Even these were unwieldy enough, but the
difficulties of manipulation were fully compensated by the results obtained.
It had been discovered, among other things, that in oblique refraction
light is separated into colors. Therefore, any small portion of the convex
lens of the telescope, being a prism, the rays proceed to the focus, separated
into prismatic colors, which make the image thus formed edged with a
fringe of color and indistinct. But, fortunately for the early telescope

makers, the degree of this aberration is independent of the focal length of
the lens; so that, by increasing this focal length and using the appropriate
eye-piece, the image can be greatly magnified, while the fringe of colors
remains about the same as when a less powerful lens is used. Hence the
advantage of Huygens's long telescope. He did not confine his efforts to
simply lengthening the focal length of his telescopes, however, but also
added to their efficiency by inventing an almost perfect achromatic eye-
piece.
In 1663 he was elected a fellow of the Royal Society of London, and in
1669 he gave to that body a concise statement of the laws governing the
collision of elastic bodies. Although the same views had been given by
Wallis and Wren a few weeks earlier, there is no doubt that Huygens's views
were reached independently; and it is probable that he had arrived at his
conclusions several years before. In the Philosophical Transactions for 1669
it is recorded that the society, being interested in the laws of the principles
of motion, a request was made that M. Huygens, Dr. Wallis, and Sir
Christopher Wren submit their views on the subject. Wallis submitted his
paper first, November 15, 1668. A month later, December 17th, Wren
imparted to the society his laws as to the nature of the collision of bodies.
And a few days later, January 5, 1669, Huygens sent in his "Rules
Concerning the Motion of Bodies after Mutual Impulse." Although
Huygens's report was received last, he was anticipated by such a brief space
of time, and his views are so clearly stated—on the whole rather more so
than those of the other two—that we give them in part here:
"1. If a hard body should strike against a body equally hard at rest, after
contact the former will rest and the latter acquire a velocity equal to that of
the moving body.
"2. But if that other equal body be likewise in motion, and moving in the
same direction, after contact they will move with reciprocal velocities.
"3. A body, however great, is moved by a body however small impelled
with any velocity whatsoever.
"5. The quantity of motion of two bodies may be either increased or
diminished by their shock; but the same quantity towards the same part
remains, after subtracting the quantity of the contrary motion.
"6. The sum of the products arising from multiplying the mass of any
hard body into the squares of its velocity is the same both before and after

the stroke.
"7. A hard body at rest will receive a greater quantity of motion from
another hard body, either greater or less than itself, by the interposition of
any third body of a mean quantity, than if it was immediately struck by the
body itself; and if the interposing body be a mean proportional between the
other two, its action upon the quiescent body will be the greatest of all."(10)
This was only one of several interesting and important communications
sent to the Royal Society during his lifetime. One of these was a report on
what he calls "Pneumatical Experiments." "Upon including in a vacuum an
insect resembling a beetle, but somewhat larger," he says, "when it seemed
to be dead, the air was readmitted, and soon after it revived; putting it again
in the vacuum, and leaving it for an hour, after which the air was
readmitted, it was observed that the insect required a longer time to recover;
including it the third time for two days, after which the air was admitted, it
was ten hours before it began to stir; but, putting it in a fourth time, for
eight days, it never afterwards recovered.... Several birds, rats, mice,
rabbits, and cats were killed in a vacuum, but if the air was admitted before
the engine was quite exhausted some of them would recover; yet none
revived that had been in a perfect vacuum.... Upon putting the weight of
eighteen grains of powder with a gauge into a receiver that held several
pounds of water, and firing the powder, it raised the mercury an inch and a
half; from which it appears that there is one-fifth of air in gunpowder, upon
the supposition that air is about one thousand times lighter than water; for in
this experiment the mercury rose to the eighteenth part of the height at
which the air commonly sustains it, and consequently the weight of
eighteen grains of powder yielded air enough to fill the eighteenth part of a
receiver that contained seven pounds of water; now this eighteenth part
contains forty-nine drachms of water; wherefore the air, that takes up an
equal space, being a thousand times lighter, weighs one-thousandth part of
forty-nine drachms, which is more than three grains and a half; it follows,
therefore, that the weight of eighteen grains of powder contains more than
three and a half of air, which is about one-fifth of eighteen grains...."
From 1665 to 1681, accepting the tempting offer made him through
Colbert, by Louis XIV., Huygens pursued his studies at the Bibliotheque du
Roi as a resident of France. Here he published his Horologium
Oscillatorium, dedicated to the king, containing, among other things, his

solution of the problem of the "centre of oscillation." This in itself was an
important step in the history of mechanics. Assuming as true that the centre
of gravity of any number of interdependent bodies cannot rise higher than
the point from which it falls, he reached correct conclusions as to the
general principle of the conservation of vis viva, although he did not
actually prove his conclusions. This was the first attempt to deal with the
dynamics of a system. In this work, also, was the true determination of the
relation between the length of a pendulum and the time of its oscillation.
In 1681 he returned to Holland, influenced, it is believed, by the attitude
that was being taken in France against his religion. Here he continued his
investigations, built his immense telescopes, and, among other things,
discovered "polarization," which is recorded in Traite de la Lumiere,
published at Leyden in 1690. Five years later he died, bequeathing his
manuscripts to the University of Leyden. It is interesting to note that he
never accepted Newton's theory of gravitation as a universal property of
matter.

XI. NEWTON AND THE COMPOSITION OF
LIGHT
Galileo, that giant in physical science of the early seventeenth century,
died in 1642. On Christmas day of the same year there was born in England
another intellectual giant who was destined to carry forward the work of
Copernicus, Kepler, and Galileo to a marvellous consummation through the
discovery of the great unifying law in accordance with which the planetary
motions are performed. We refer, of course, to the greatest of English
physical scientists, Isaac Newton, the Shakespeare of the scientific world.
Born thus before the middle of the seventeenth century, Newton lived
beyond the first quarter of the eighteenth (1727). For the last forty years of
that period his was the dominating scientific personality of the world. With
full propriety that time has been spoken of as the "Age of Newton."
Yet the man who was to achieve such distinction gave no early
premonition of future greatness. He was a sickly child from birth, and a boy
of little seeming promise. He was an indifferent student, yet, on the other
hand, he cared little for the common amusements of boyhood. He early
exhibited, however, a taste for mechanical contrivances, and spent much
time in devising windmills, water-clocks, sun-dials, and kites. While other
boys were interested only in having kites that would fly, Newton—at least
so the stories of a later time would have us understand—cared more for the
investigation of the seeming principles involved, or for testing the best
methods of attaching the strings, or the best materials to be used in
construction.
Meanwhile the future philosopher was acquiring a taste for reading and
study, delving into old volumes whenever he found an opportunity. These
habits convinced his relatives that it was useless to attempt to make a
farmer of the youth, as had been their intention. He was therefore sent back
to school, and in the summer of 1661 he matriculated at Trinity College,
Cambridge. Even at college Newton seems to have shown no unusual
mental capacity, and in 1664, when examined for a scholarship by Dr.
Barrow, that gentleman is said to have formed a poor opinion of the

applicant. It is said that the knowledge of the estimate placed upon his
abilities by his instructor piqued Newton, and led him to take up in earnest
the mathematical studies in which he afterwards attained such distinction.
The study of Euclid and Descartes's "Geometry" roused in him a latent
interest in mathematics, and from that time forward his investigations were
carried on with enthusiasm. In 1667 he was elected Fellow of Trinity
College, taking the degree of M.A. the following spring.
It will thus appear that Newton's boyhood and early manhood were
passed during that troublous time in British political annals which saw the
overthrow of Charles I., the autocracy of Cromwell, and the eventual
restoration of the Stuarts. His maturer years witnessed the overthrow of the
last Stuart and the reign of the Dutchman, William of Orange. In his old age
he saw the first of the Hanoverians mount the throne of England. Within a
decade of his death such scientific path-finders as Cavendish, Black, and
Priestley were born—men who lived on to the close of the eighteenth
century. In a full sense, then, the age of Newton bridges the gap from that
early time of scientific awakening under Kepler and Galileo to the time
which we of the twentieth century think of as essentially modern.
THE COMPOSITION OF WHITE LIGHT
In December, 1672, Newton was elected a Fellow of the Royal Society,
and at this meeting a paper describing his invention of the refracting
telescope was read. A few days later he wrote to the secretary, making some
inquiries as to the weekly meetings of the society, and intimating that he
had an account of an interesting discovery that he wished to lay before the
society. When this communication was made public, it proved to be an
explanation of the discovery of the composition of white light. We have
seen that the question as to the nature of color had commanded the attention
of such investigators as Huygens, but that no very satisfactory solution of
the question had been attained. Newton proved by demonstrative
experiments that white light is composed of the blending of the rays of
diverse colors, and that the color that we ascribe to any object is merely due
to the fact that the object in question reflects rays of that color, absorbing
the rest. That white light is really made up of many colors blended would
seem incredible had not the experiments by which this composition is
demonstrated become familiar to every one. The experiments were
absolutely novel when Newton brought them forward, and his

demonstration of the composition of light was one of the most striking
expositions ever brought to the attention of the Royal Society. It is hardly
necessary to add that, notwithstanding the conclusive character of Newton's
work, his explanations did not for a long time meet with general
acceptance.
Newton was led to his discovery by some experiments made with an
ordinary glass prism applied to a hole in the shutter of a darkened room, the
refracted rays of the sunlight being received upon the opposite wall and
forming there the familiar spectrum. "It was a very pleasing diversion," he
wrote, "to view the vivid and intense colors produced thereby; and after a
time, applying myself to consider them very circumspectly, I became
surprised to see them in varying form, which, according to the received
laws of refraction, I expected should have been circular. They were
terminated at the sides with straight lines, but at the ends the decay of light
was so gradual that it was difficult to determine justly what was their figure,
yet they seemed semicircular.
"Comparing the length of this colored spectrum with its breadth, I found
it almost five times greater; a disproportion so extravagant that it excited
me to a more than ordinary curiosity of examining from whence it might
proceed. I could scarce think that the various thicknesses of the glass, or the
termination with shadow or darkness, could have any influence on light to
produce such an effect; yet I thought it not amiss, first, to examine those
circumstances, and so tried what would happen by transmitting light
through parts of the glass of divers thickness, or through holes in the
window of divers bigness, or by setting the prism without so that the light
might pass through it and be refracted before it was transmitted through the
hole; but I found none of those circumstances material. The fashion of the
colors was in all these cases the same.
"Then I suspected whether by any unevenness of the glass or other
contingent irregularity these colors might be thus dilated. And to try this I
took another prism like the former, and so placed it that the light, passing
through them both, might be refracted contrary ways, and so by the latter
returned into that course from which the former diverted it. For, by this
means, I thought, the regular effects of the first prism would be destroyed
by the second prism, but the irregular ones more augmented by the
multiplicity of refractions. The event was that the light, which by the first

prism was diffused into an oblong form, was by the second reduced into an
orbicular one with as much regularity as when it did not all pass through
them. So that, whatever was the cause of that length, 'twas not any
contingent irregularity.
"I then proceeded to examine more critically what might be effected by
the difference of the incidence of rays coming from divers parts of the sun;
and to that end measured the several lines and angles belonging to the
image. Its distance from the hole or prism was 22 feet; its utmost length 13
1/4 inches; its breadth 2 5/8; the diameter of the hole 1/4 of an inch; the
angle which the rays, tending towards the middle of the image, made with
those lines, in which they would have proceeded without refraction, was 44
degrees 56'; and the vertical angle of the prism, 63 degrees 12'. Also the
refractions on both sides of the prism—that is, of the incident and emergent
rays—were, as near as I could make them, equal, and consequently about
54 degrees 4'; and the rays fell perpendicularly upon the wall. Now,
subducting the diameter of the hole from the length and breadth of the
image, there remains 13 inches the length, and 2 3/8 the breadth,
comprehended by those rays, which, passing through the centre of the said
hole, which that breadth subtended, was about 31', answerable to the sun's
diameter; but the angle which its length subtended was more than five such
diameters, namely 2 degrees 49'.
"Having made these observations, I first computed from them the
refractive power of the glass, and found it measured by the ratio of the sines
20 to 31. And then, by that ratio, I computed the refractions of two rays
flowing from opposite parts of the sun's discus, so as to differ 31' in their
obliquity of incidence, and found that the emergent rays should have
comprehended an angle of 31', as they did, before they were incident.
"But because this computation was founded on the hypothesis of the
proportionality of the sines of incidence and refraction, which though by
my own experience I could not imagine to be so erroneous as to make that
angle but 31', which in reality was 2 degrees 49', yet my curiosity caused
me again to make my prism. And having placed it at my window, as before,
I observed that by turning it a little about its axis to and fro, so as to vary its
obliquity to the light more than an angle of 4 degrees or 5 degrees, the
colors were not thereby sensibly translated from their place on the wall, and
consequently by that variation of incidence the quantity of refraction was

not sensibly varied. By this experiment, therefore, as well as by the former
computation, it was evident that the difference of the incidence of rays
flowing from divers parts of the sun could not make them after decussation
diverge at a sensibly greater angle than that at which they before converged;
which being, at most, but about 31' or 32', there still remained some other
cause to be found out, from whence it could be 2 degrees 49'."
All this caused Newton to suspect that the rays, after their trajection
through the prism, moved in curved rather than in straight lines, thus
tending to be cast upon the wall at different places according to the amount
of this curve. His suspicions were increased, also, by happening to recall
that a tennis-ball sometimes describes such a curve when "cut" by a tennis-
racket striking the ball obliquely.
"For a circular as well as a progressive motion being communicated to it
by the stroke," he says, "its parts on that side where the motions conspire
must press and beat the contiguous air more violently than on the other, and
there excite a reluctancy and reaction of the air proportionately greater. And
for the same reason, if the rays of light should possibly be globular bodies,
and by their oblique passage out of one medium into another acquire a
circulating motion, they ought to feel the greater resistance from the
ambient ether on that side where the motions conspire, and thence be
continually bowed to the other. But notwithstanding this plausible ground of
suspicion, when I came to examine it I could observe no such curvity in
them. And, besides (which was enough for my purpose), I observed that the
difference 'twixt the length of the image and diameter of the hole through
which the light was transmitted was proportionable to their distance.
"The gradual removal of these suspicions at length led me to the
experimentum crucis, which was this: I took two boards, and, placing one
of them close behind the prism at the window, so that the light must pass
through a small hole, made in it for the purpose, and fall on the other board,
which I placed at about twelve feet distance, having first made a small hole
in it also, for some of the incident light to pass through. Then I placed
another prism behind this second board, so that the light trajected through
both the boards might pass through that also, and be again refracted before
it arrived at the wall. This done, I took the first prism in my hands and
turned it to and fro slowly about its axis, so much as to make the several
parts of the image, cast on the second board, successively pass through the

hole in it, that I might observe to what places on the wall the second prism
would refract them. And I saw by the variation of these places that the light,
tending to that end of the image towards which the refraction of the first
prism was made, did in the second prism suffer a refraction considerably
greater than the light tending to the other end. And so the true cause of the
length of that image was detected to be no other than that LIGHT consists
of RAYS DIFFERENTLY REFRANGIBLE, which, without any respect to
a difference in their incidence, were, according to their degrees of
refrangibility, transmitted towards divers parts of the wall."(1)
THE NATURE OF COLOR
Having thus proved the composition of light, Newton took up an
exhaustive discussion as to colors, which cannot be entered into at length
here. Some of his remarks on the subject of compound colors, however,
may be stated in part. Newton's views are of particular interest in this
connection, since, as we have already pointed out, the question as to what
constituted color could not be agreed upon by the philosophers. Some held
that color was an integral part of the substance; others maintained that it
was simply a reflection from the surface; and no scientific explanation had
been generally accepted. Newton concludes his paper as follows:
"I might add more instances of this nature, but I shall conclude with the
general one that the colors of all natural bodies have no other origin than
this, that they are variously qualified to reflect one sort of light in greater
plenty than another. And this I have experimented in a dark room by
illuminating those bodies with uncompounded light of divers colors. For by
that means any body may be made to appear of any color. They have there
no appropriate color, but ever appear of the color of the light cast upon
them, but yet with this difference, that they are most brisk and vivid in the
light of their own daylight color. Minium appeareth there of any color
indifferently with which 'tis illustrated, but yet most luminous in red; and so
Bise appeareth indifferently of any color with which 'tis illustrated, but yet
most luminous in blue. And therefore Minium reflecteth rays of any color,
but most copiously those indued with red; and consequently, when
illustrated with daylight—that is, with all sorts of rays promiscuously
blended—those qualified with red shall abound most in the reflected light,
and by their prevalence cause it to appear of that color. And for the same
reason, Bise, reflecting blue most copiously, shall appear blue by the excess

of those rays in its reflected light; and the like of other bodies. And that this
is the entire and adequate cause of their colors is manifest, because they
have no power to change or alter the colors of any sort of rays incident
apart, but put on all colors indifferently with which they are enlightened."
(2)
This epoch-making paper aroused a storm of opposition. Some of
Newton's opponents criticised his methods, others even doubted the truth of
his experiments. There was one slight mistake in Newton's belief that all
prisms would give a spectrum of exactly the same length, and it was some
time before he corrected this error. Meanwhile he patiently met and
answered the arguments of his opponents until he began to feel that patience
was no longer a virtue. At one time he even went so far as to declare that,
once he was "free of this business," he would renounce scientific research
forever, at least in a public way. Fortunately for the world, however, he did
not adhere to this determination, but went on to even greater discoveries—
which, it may be added, involved still greater controversies.
In commenting on Newton's discovery of the composition of light,
Voltaire said: "Sir Isaac Newton has demonstrated to the eye, by the bare
assistance of a prism, that light is a composition of colored rays, which,
being united, form white color. A single ray is by him divided into seven,
which all fall upon a piece of linen or a sheet of white paper, in their order
one above the other, and at equal distances. The first is red, the second
orange, the third yellow, the fourth green, the fifth blue, the sixth indigo, the
seventh a violet purple. Each of these rays transmitted afterwards by a
hundred other prisms will never change the color it bears; in like manner as
gold, when completely purged from its dross, will never change afterwards
in the crucible."(3)

XII. NEWTON AND THE LAW OF
GRAVITATION
We come now to the story of what is by common consent the greatest of
scientific achievements. The law of universal gravitation is the most far-
reaching principle as yet discovered. It has application equally to the
minutest particle of matter and to the most distant suns in the universe, yet
it is amazing in its very simplicity. As usually phrased, the law is this: That
every particle of matter in the universe attracts every other particle with a
force that varies directly with the mass of the particles and inversely as the
squares of their mutual distance. Newton did not vault at once to the full
expression of this law, though he had formulated it fully before he gave the
results of his investigations to the world. We have now to follow the steps
by which he reached this culminating achievement.
At the very beginning we must understand that the idea of universal
gravitation was not absolutely original with Newton. Away back in the old
Greek days, as we have seen, Anaxagoras conceived and clearly expressed
the idea that the force which holds the heavenly bodies in their orbits may
be the same that operates upon substances at the surface of the earth. With
Anaxagoras this was scarcely more than a guess. After his day the idea
seems not to have been expressed by any one until the seventeenth century's
awakening of science. Then the consideration of Kepler's Third Law of
planetary motion suggested to many minds perhaps independently the
probability that the force hitherto mentioned merely as centripetal, through
the operation of which the planets are held in their orbits is a force varying
inversely as the square of the distance from the sun. This idea had come to
Robert Hooke, to Wren, and perhaps to Halley, as well as to Newton; but as
yet no one had conceived a method by which the validity of the suggestion
might be tested. It was claimed later on by Hooke that he had discovered a
method demonstrating the truth of the theory of inverse squares, and after
the full announcement of Newton's discovery a heated controversy was
precipitated in which Hooke put forward his claims with accustomed
acrimony. Hooke, however, never produced his demonstration, and it may
well be doubted whether he had found a method which did more than

vaguely suggest the law which the observations of Kepler had partially
revealed. Newton's great merit lay not so much in conceiving the law of
inverse squares as in the demonstration of the law. He was led to this
demonstration through considering the orbital motion of the moon.
According to the familiar story, which has become one of the classic myths
of science, Newton was led to take up the problem through observing the
fall of an apple. Voltaire is responsible for the story, which serves as well as
another; its truth or falsity need not in the least concern us. Suffice it that
through pondering on the familiar fact of terrestrial gravitation, Newton was
led to question whether this force which operates so tangibly here at the
earth's surface may not extend its influence out into the depths of space, so
as to include, for example, the moon. Obviously some force pulls the moon
constantly towards the earth; otherwise that body would fly off at a tangent
and never return. May not this so-called centripetal force be identical with
terrestrial gravitation? Such was Newton's query. Probably many another
man since Anaxagoras had asked the same question, but assuredly Newton
was the first man to find an answer.
The thought that suggested itself to Newton's mind was this: If we make
a diagram illustrating the orbital course of the moon for any given period,
say one minute, we shall find that the course of the moon departs from a
straight line during that period by a measurable distance—that: is to say, the
moon has been virtually pulled towards the earth by an amount that is
represented by the difference between its actual position at the end of the
minute under observation and the position it would occupy had its course
been tangential, as, according to the first law of motion, it must have been
had not some force deflected it towards the earth. Measuring the deflection
in question—which is equivalent to the so-called versed sine of the arc
traversed—we have a basis for determining the strength of the deflecting
force. Newton constructed such a diagram, and, measuring the amount of
the moon's departure from a tangential rectilinear course in one minute,
determined this to be, by his calculation, thirteen feet. Obviously, then, the
force acting upon the moon is one that would cause that body to fall
towards the earth to the distance of thirteen feet in the first minute of its
fall. Would such be the force of gravitation acting at the distance of the
moon if the power of gravitation varies inversely as the square of the
distance? That was the tangible form in which the problem presented itself
to Newton. The mathematical solution of the problem was simple enough. It

is based on a comparison of the moon's distance with the length of the
earth's radius. On making this calculation, Newton found that the pull of
gravitation—if that were really the force that controls the moon—gives that
body a fall of slightly over fifteen feet in the first minute, instead of thirteen
feet. Here was surely a suggestive approximation, yet, on the other band,
the discrepancy seemed to be too great to warrant him in the supposition
that he had found the true solution. He therefore dismissed the matter from
his mind for the time being, nor did he return to it definitely for some years.
{illustration caption = DIAGRAM TO ILLUSTRATE NEWTON'S LAW
OF GRAVITATION (E represents the earth and A the moon. Were the
earth's pull on the moon to cease, the moon's inertia would cause it to take
the tangential course, AB. On the other hand, were the moon's motion to be
stopped for an instant, the moon would fall directly towards the earth, along
the line AD. The moon's actual orbit, resulting from these component
forces, is AC. Let AC represent the actual flight of the moon in one minute.
Then BC, which is obviously equal to AD, represents the distance which the
moon virtually falls towards the earth in one minute. Actual computation,
based on measurements of the moon's orbit, showed this distance to be
about fifteen feet. Another computation showed that this is the distance that
the moon would fall towards the earth under the influence of gravity, on the
supposition that the force of gravity decreases inversely with the square of
the distance; the basis of comparison being furnished by falling bodies at
the surface of the earth. Theory and observations thus coinciding, Newton
was justified in declaring that the force that pulls the moon towards the
earth and keeps it in its orbit, is the familiar force of gravity, and that this
varies inversely as the square of the distance.)}
It was to appear in due time that Newton's hypothesis was perfectly valid
and that his method of attempted demonstration was equally so. The
difficulty was that the earth's proper dimensions were not at that time
known. A wrong estimate of the earth's size vitiated all the other
calculations involved, since the measurement of the moon's distance
depends upon the observation of the parallax, which cannot lead to a correct
computation unless the length of the earth's radius is accurately known.
Newton's first calculation was made as early as 1666, and it was not until
1682 that his attention was called to a new and apparently accurate
measurement of a degree of the earth's meridian made by the French

astronomer Picard. The new measurement made a degree of the earth's
surface 69.10 miles, instead of sixty miles.
Learning of this materially altered calculation as to the earth's size,
Newton was led to take up again his problem of the falling moon. As he
proceeded with his computation, it became more and more certain that this
time the result was to harmonize with the observed facts. As the story goes,
he was so completely overwhelmed with emotion that he was forced to ask
a friend to complete the simple calculation. That story may well be true, for,
simple though the computation was, its result was perhaps the most
wonderful demonstration hitherto achieved in the entire field of science.
Now at last it was known that the force of gravitation operates at the
distance of the moon, and holds that body in its elliptical orbit, and it
required but a slight effort of the imagination to assume that the force which
operates through such a reach of space extends its influence yet more
widely. That such is really the case was demonstrated presently through
calculations as to the moons of Jupiter and by similar computations
regarding the orbital motions of the various planets. All results
harmonizing, Newton was justified in reaching the conclusion that
gravitation is a universal property of matter. It remained, as we shall see, for
nineteenth-century scientists to prove that the same force actually operates
upon the stars, though it should be added that this demonstration merely
fortified a belief that had already found full acceptance.
Having thus epitomized Newton's discovery, we must now take up the
steps of his progress somewhat in detail, and state his theories and their
demonstration in his own words. Proposition IV., theorem 4, of his Principia
is as follows:
"That the moon gravitates towards the earth and by the force of gravity is
continually drawn off from a rectilinear motion and retained in its orbit.
"The mean distance of the moon from the earth, in the syzygies in semi-
diameters of the earth, is, according to Ptolemy and most astronomers, 59;
according to Vendelin and Huygens, 60; to Copernicus, 60 1/3; to Street, 60
2/3; and to Tycho, 56 1/2. But Tycho, and all that follow his tables of
refractions, making the refractions of the sun and moon (altogether against
the nature of light) to exceed the refractions of the fixed stars, and that by
four or five minutes NEAR THE HORIZON, did thereby increase the
moon's HORIZONTAL parallax by a like number of minutes, that is, by a

twelfth or fifteenth part of the whole parallax. Correct this error and the
distance will become about 60 1/2 semi-diameters of the earth, near to what
others have assigned. Let us assume the mean distance of 60 diameters in
the syzygies; and suppose one revolution of the moon, in respect to the
fixed stars, to be completed in 27d. 7h. 43', as astronomers have
determined; and the circumference of the earth to amount to 123,249,600
Paris feet, as the French have found by mensuration. And now, if we
imagine the moon, deprived of all motion, to be let go, so as to descend
towards the earth with the impulse of all that force by which (by Cor. Prop.
iii.) it is retained in its orb, it will in the space of one minute of time
describe in its fall 15 1/12 Paris feet. For the versed sine of that arc which
the moon, in the space of one minute of time, would by its mean motion
describe at the distance of sixty semi-diameters of the earth, is nearly 15
1/12 Paris feet, or more accurately 15 feet, 1 inch, 1 line 4/9. Wherefore,
since that force, in approaching the earth, increases in the reciprocal-
duplicate proportion of the distance, and upon that account, at the surface of
the earth, is 60 x 60 times greater than at the moon, a body in our regions,
falling with that force, ought in the space of one minute of time to describe
60 x 60 x 15 1/12 Paris feet; and in the space of one second of time, to
describe 15 1/12 of those feet, or more accurately, 15 feet, 1 inch, 1 line 4/9.
And with this very force we actually find that bodies here upon earth do
really descend; for a pendulum oscillating seconds in the latitude of Paris
will be 3 Paris feet, and 8 lines 1/2 in length, as Mr. Huygens has observed.
And the space which a heavy body describes by falling in one second of
time is to half the length of the pendulum in the duplicate ratio of the
circumference of a circle to its diameter (as Mr. Huygens has also shown),
and is therefore 15 Paris feet, 1 inch, 1 line 4/9. And therefore the force by
which the moon is retained in its orbit is that very same force which we
commonly call gravity; for, were gravity another force different from that,
then bodies descending to the earth with the joint impulse of both forces
would fall with a double velocity, and in the space of one second of time
would describe 30 1/6 Paris feet; altogether against experience."(1)
All this is beautifully clear, and its validity has never in recent
generations been called in question; yet it should be explained that the
argument does not amount to an actually indisputable demonstration. It is at
least possible that the coincidence between the observed and computed
motion of the moon may be a mere coincidence and nothing more. This

probability, however, is so remote that Newton is fully justified in
disregarding it, and, as has been said, all subsequent generations have
accepted the computation as demonstrative.
Let us produce now Newton's further computations as to the other
planetary bodies, passing on to his final conclusion that gravity is a
universal force.

"PROPOSITION V., THEOREM V.

"That the circumjovial planets gravitate towards Jupiter; the
circumsaturnal towards Saturn; the circumsolar towards the sun; and by the
forces of their gravity are drawn off from rectilinear motions, and retained
in curvilinear orbits.
"For the revolutions of the circumjovial planets about Jupiter, of the
circumsaturnal about Saturn, and of Mercury and Venus and the other
circumsolar planets about the sun, are appearances of the same sort with the
revolution of the moon about the earth; and therefore, by Rule ii., must be
owing to the same sort of causes; especially since it has been demonstrated
that the forces upon which those revolutions depend tend to the centres of
Jupiter, of Saturn, and of the sun; and that those forces, in receding from
Jupiter, from Saturn, and from the sun, decrease in the same proportion, and
according to the same law, as the force of gravity does in receding from the
earth.
"COR. 1.—There is, therefore, a power of gravity tending to all the
planets; for doubtless Venus, Mercury, and the rest are bodies of the same
sort with Jupiter and Saturn. And since all attraction (by Law iii.) is mutual,
Jupiter will therefore gravitate towards all his own satellites, Saturn towards
his, the earth towards the moon, and the sun towards all the primary planets.
"COR. 2.—The force of gravity which tends to any one planet is
reciprocally as the square of the distance of places from the planet's centre.
"COR. 3.—All the planets do mutually gravitate towards one another, by
Cor. 1 and 2, and hence it is that Jupiter and Saturn, when near their
conjunction, by their mutual attractions sensibly disturb each other's
motions. So the sun disturbs the motions of the moon; and both sun and
moon disturb our sea, as we shall hereafter explain.

"SCHOLIUM

"The force which retains the celestial bodies in their orbits has been
hitherto called centripetal force; but it being now made plain that it can be
no other than a gravitating force, we shall hereafter call it gravity. For the
cause of the centripetal force which retains the moon in its orbit will extend
itself to all the planets by Rules i., ii., and iii.

"PROPOSITION VI., THEOREM VI.

"That all bodies gravitate towards every planet; and that the weights of
the bodies towards any the same planet, at equal distances from the centre
of the planet, are proportional to the quantities of matter which they
severally contain.
"It has been now a long time observed by others that all sorts of heavy
bodies (allowance being made for the inability of retardation which they
suffer from a small power of resistance in the air) descend to the earth
FROM EQUAL HEIGHTS in equal times; and that equality of times we
may distinguish to a great accuracy by help of pendulums. I tried the thing
in gold, silver, lead, glass, sand, common salt, wood, water, and wheat. I
provided two wooden boxes, round and equal: I filled the one with wood,
and suspended an equal weight of gold (as exactly as I could) in the centre
of oscillation of the other. The boxes hanging by eleven feet, made a couple
of pendulums exactly equal in weight and figure, and equally receiving the
resistance of the air. And, placing the one by the other, I observed them to
play together forward and backward, for a long time, with equal vibrations.
And therefore the quantity of matter in gold was to the quantity of matter in
the wood as the action of the motive force (or vis motrix) upon all the gold
to the action of the same upon all the wood—that is, as the weight of the
one to the weight of the other: and the like happened in the other bodies. By
these experiments, in bodies of the same weight, I could manifestly have
discovered a difference of matter less than the thousandth part of the whole,
had any such been. But, without all doubt, the nature of gravity towards the
planets is the same as towards the earth. For, should we imagine our
terrestrial bodies removed to the orb of the moon, and there, together with
the moon, deprived of all motion, to be let go, so as to fall together towards
the earth, it is certain, from what we have demonstrated before, that, in
equal times, they would describe equal spaces with the moon, and of
consequence are to the moon, in quantity and matter, as their weights to its
weight.

"Moreover, since the satellites of Jupiter perform their revolutions in
times which observe the sesquiplicate proportion of their distances from
Jupiter's centre, their accelerative gravities towards Jupiter will be
reciprocally as the square of their distances from Jupiter's centre—that is,
equal, at equal distances. And, therefore, these satellites, if supposed to fall
TOWARDS JUPITER from equal heights, would describe equal spaces in
equal times, in like manner as heavy bodies do on our earth. And, by the
same argument, if the circumsolar planets were supposed to be let fall at
equal distances from the sun, they would, in their descent towards the sun,
describe equal spaces in equal times. But forces which equally accelerate
unequal bodies must be as those bodies—that is to say, the weights of the
planets (TOWARDS THE SUN) must be as their quantities of matter.
Further, that the weights of Jupiter and his satellites towards the sun are
proportional to the several quantities of their matter, appears from the
exceedingly regular motions of the satellites. For if some of these bodies
were more strongly attracted to the sun in proportion to their quantity of
matter than others, the motions of the satellites would be disturbed by that
inequality of attraction. If at equal distances from the sun any satellite, in
proportion to the quantity of its matter, did gravitate towards the sun with a
force greater than Jupiter in proportion to his, according to any given
proportion, suppose d to e; then the distance between the centres of the sun
and of the satellite's orbit would be always greater than the distance
between the centres of the sun and of Jupiter nearly in the subduplicate of
that proportion: as by some computations I have found. And if the satellite
did gravitate towards the sun with a force, lesser in the proportion of e to d,
the distance of the centre of the satellite's orb from the sun would be less
than the distance of the centre of Jupiter from the sun in the subduplicate of
the same proportion. Therefore, if at equal distances from the sun, the
accelerative gravity of any satellite towards the sun were greater or less
than the accelerative gravity of Jupiter towards the sun by one-one-
thousandth part of the whole gravity, the distance of the centre of the
satellite's orbit from the sun would be greater or less than the distance of
Jupiter from the sun by one one-two-thousandth part of the whole distance
—that is, by a fifth part of the distance of the utmost satellite from the
centre of Jupiter; an eccentricity of the orbit which would be very sensible.
But the orbits of the satellites are concentric to Jupiter, and therefore the
accelerative gravities of Jupiter and of all its satellites towards the sun, at

equal distances from the sun, are as their several quantities of matter; and
the weights of the moon and of the earth towards the sun are either none, or
accurately proportional to the masses of matter which they contain.
"COR. 5.—The power of gravity is of a different nature from the power
of magnetism; for the magnetic attraction is not as the matter attracted.
Some bodies are attracted more by the magnet; others less; most bodies not
at all. The power of magnetism in one and the same body may be increased
and diminished; and is sometimes far stronger, for the quantity of matter,
than the power of gravity; and in receding from the magnet decreases not in
the duplicate, but almost in the triplicate proportion of the distance, as
nearly as I could judge from some rude observations.

"PROPOSITION VII., THEOREM VII.

"That there is a power of gravity tending to all bodies, proportional to the
several quantities of matter which they contain.
"That all the planets mutually gravitate one towards another we have
proved before; as well as that the force of gravity towards every one of
them considered apart, is reciprocally as the square of the distance of places
from the centre of the planet. And thence it follows, that the gravity tending
towards all the planets is proportional to the matter which they contain.
"Moreover, since all the parts of any planet A gravitates towards any
other planet B; and the gravity of every part is to the gravity of the whole as
the matter of the part is to the matter of the whole; and to every action
corresponds a reaction; therefore the planet B will, on the other hand,
gravitate towards all the parts of planet A, and its gravity towards any one
part will be to the gravity towards the whole as the matter of the part to the
matter of the whole. Q.E.D.
"HENCE IT WOULD APPEAR THAT the force of the whole must arise
from the force of the component parts."
Newton closes this remarkable Book iii. with the following words:
"Hitherto we have explained the phenomena of the heavens and of our
sea by the power of gravity, but have not yet assigned the cause of this
power. This is certain, that it must proceed from a cause that penetrates to
the very centre of the sun and planets, without suffering the least diminution
of its force; that operates not according to the quantity of the surfaces of the
particles upon which it acts (as mechanical causes used to do), but

according to the quantity of solid matter which they contain, and propagates
its virtue on all sides to immense distances, decreasing always in the
duplicate proportions of the distances. Gravitation towards the sun is made
up out of the gravitations towards the several particles of which the body of
the sun is composed; and in receding from the sun decreases accurately in
the duplicate proportion of the distances as far as the orb of Saturn, as
evidently appears from the quiescence of the aphelions of the planets; nay,
and even to the remotest aphelions of the comets, if those aphelions are also
quiescent. But hitherto I have not been able to discover the cause of those
properties of gravity from phenomena, and I frame no hypothesis; for
whatever is not deduced from the phenomena is to be called an hypothesis;
and hypotheses, whether metaphysical or physical, whether of occult
qualities or mechanical, have no place in experimental philosophy.... And to
us it is enough that gravity does really exist, and act according to the laws
which we have explained, and abundantly serves to account for all the
motions of the celestial bodies and of our sea."(2)
The very magnitude of the importance of the theory of universal
gravitation made its general acceptance a matter of considerable time after
the actual discovery. This opposition had of course been foreseen by
Newton, and, much as he dreaded controversy, he was prepared to face it
and combat it to the bitter end. He knew that his theory was right; it
remained for him to convince the world of its truth. He knew that some of
his contemporary philosophers would accept it at once; others would at first
doubt, question, and dispute, but finally accept; while still others would
doubt and dispute until the end of their days. This had been the history of
other great discoveries; and this will probably be the history of most great
discoveries for all time. But in this case the discoverer lived to see his
theory accepted by practically all the great minds of his time.
Delambre is authority for the following estimate of Newton by Lagrange.
"The celebrated Lagrange," he says, "who frequently asserted that Newton
was the greatest genius that ever existed, used to add—'and the most
fortunate, for we cannot find MORE THAN ONCE a system of the world to
establish.'" With pardonable exaggeration the admiring followers of the
great generalizer pronounced this epitaph:

"Nature and Nature's laws lay hid in night;
God said 'Let Newton be!' and all was light."

XIII. INSTRUMENTS OF PRECISION IN THE
AGE OF NEWTON
During the Newtonian epoch there were numerous important inventions
of scientific instruments, as well as many improvements made upon the
older ones. Some of these discoveries have been referred to briefly in other
places, but their importance in promoting scientific investigation warrants a
fuller treatment of some of the more significant.
Many of the errors that had arisen in various scientific calculations before
the seventeenth century may be ascribed to the crudeness and inaccuracy in
the construction of most scientific instruments. Scientists had not as yet
learned that an approach to absolute accuracy was necessary in every
investigation in the field of science, and that such accuracy must be
extended to the construction of the instruments used in these investigations
and observations. In astronomy it is obvious that instruments of delicate
exactness are most essential; yet Tycho Brahe, who lived in the sixteenth
century, is credited with being the first astronomer whose instruments show
extreme care in construction.
It seems practically settled that the first telescope was invented in
Holland in 1608; but three men, Hans Lippershey, James Metius, and
Zacharias Jansen, have been given the credit of the invention at different
times. It would seem from certain papers, now in the library of the
University of Leyden, and included in Huygens's papers, that Lippershey
was probably the first to invent a telescope and to describe his invention.
The story is told that Lippershey, who was a spectacle-maker, stumbled by
accident upon the discovery that when two lenses are held at a certain
distance apart, objects at a distance appear nearer and larger. Having made
this discovery, he fitted two lenses with a tube so as to maintain them at the
proper distance, and thus constructed the first telescope.
It was Galileo, however, as referred to in a preceding chapter, who first
constructed a telescope based on his knowledge of the laws of refraction. In
1609, having heard that an instrument had been invented, consisting of two
lenses fixed in a tube, whereby objects were made to appear larger and

nearer, he set about constructing such an instrument that should follow out
the known effects of refraction. His first telescope, made of two lenses fixed
in a lead pipe, was soon followed by others of improved types, Galileo
devoting much time and labor to perfecting lenses and correcting errors. In
fact, his work in developing the instrument was so important that the
telescope came gradually to be known as the "Galilean telescope."
In the construction of his telescope Galileo made use of a convex and a
concave lens; but shortly after this Kepler invented an instrument in which
both the lenses used were convex. This telescope gave a much larger field
of view than the Galilean telescope, but did not give as clear an image, and
in consequence did not come into general use until the middle of the
seventeenth century. The first powerful telescope of this type was made by
Huygens and his brother. It was of twelve feet focal length, and enabled
Huygens to discover a new satellite of Saturn, and to determine also the true
explanation of Saturn's ring.
It was Huygens, together with Malvasia and Auzout, who first applied the
micrometer to the telescope, although the inventor of the first micrometer
was William Gascoigne, of Yorkshire, about 1636. The micrometer as used
in telescopes enables the observer to measure accurately small angular
distances. Before the invention of the telescope such measurements were
limited to the angle that could be distinguished by the naked eye, and were,
of course, only approximately accurate. Even very careful observers, such
as Tycho Brahe, were able to obtain only fairly accurate results. But by
applying Gascoigne's invention to the telescope almost absolute accuracy
became at once possible. The principle of Gascoigne's micrometer was that
of two pointers lying parallel, and in this position pointing to zero. These
were arranged so that the turning of a single screw separated or
approximated them at will, and the angle thus formed could be determined
with absolute accuracy.
Huygens's micrometer was a slip of metal of variable breadth inserted at
the focus of the telescope. By observing at what point this exactly covered
an object under examination, and knowing the focal length of the telescope
and the width of the metal, he could then deduce the apparent angular
breadth of the object. Huygens discovered also that an object placed in the
common focus of the two lenses of a Kepler telescope appears distinct and
clearly defined. The micrometers of Malvasia, and later of Auzout and

Picard, are the development of this discovery. Malvasia's micrometer, which
he described in 1662, consisted of fine silver wires placed at right-angles at
the focus of his telescope.
As telescopes increased in power, however, it was found that even the
finest wire, or silk filaments, were much too thick for astronomical
observations, as they obliterated the image, and so, finally, the spider-web
came into use and is still used in micrometers and other similar instruments.
Before that time, however, the fine crossed wires had revolutionized
astronomical observations. "We may judge how great was the improvement
which these contrivances introduced into the art of observing," says
Whewell, "by finding that Hevelius refused to adopt them because they
would make all the old observations of no value. He had spent a laborious
and active life in the exercise of the old methods, and could not bear to
think that all the treasures which he had accumulated had lost their worth by
the discovery of a new mine of richer ones."(1)
Until the time of Newton, all the telescopes in use were either of the
Galilean or Keplerian type, that is, refractors. But about the year 1670
Newton constructed his first reflecting telescope, which was greatly
superior to, although much smaller than, the telescopes then in use. He was
led to this invention by his experiments with light and colors. In 1671 he
presented to the Royal Society a second and somewhat larger telescope,
which he had made; and this type of instrument was little improved upon
until the introduction of the achromatic telescope, invented by Chester
Moor Hall in 1733.
As is generally known, the element of accurate measurements of time
plays an important part in the measurements of the movements of the
heavenly bodies. In fact, one was scarcely possible without the other, and as
it happened it was the same man, Huygens, who perfected Kepler's
telescope and invented the pendulum clock. The general idea had been
suggested by Galileo; or, better perhaps, the equal time occupied by the
successive oscillations of the pendulum had been noted by him. He had not
been able, however, to put this discovery to practical account. But in 1656
Huygens invented the necessary machinery for maintaining the motion of
the pendulum and perfected several accurate clocks. These clocks were of
invaluable assistance to the astronomers, affording as they did a means of
keeping time "more accurate than the sun itself." When Picard had

corrected the variation caused by heat and cold acting upon the pendulum
rod by combining metals of different degrees of expansibility, a high degree
of accuracy was possible.
But while the pendulum clock was an unequalled stationary time-piece, it
was useless in such unstable situations as, for example, on shipboard. But
here again Huygens played a prominent part by first applying the coiled
balance-spring for regulating watches and marine clocks. The idea of
applying a spring to the balance-wheel was not original with Huygens,
however, as it had been first conceived by Robert Hooke; but Huygens's
application made practical Hooke's idea. In England the importance of
securing accurate watches or marine clocks was so fully appreciated that a
reward of L20,000 sterling was offered by Parliament as a stimulus to the
inventor of such a time-piece. The immediate incentive for this offer was
the obvious fact that with such an instrument the determination of the
longitude of places would be much simplified. Encouraged by these offers,
a certain carpenter named Harrison turned his attention to the subject of
watch-making, and, after many years of labor, in 1758 produced a spring
time-keeper which, during a sea-voyage occupying one hundred and sixty-
one days, varied only one minute and five seconds. This gained for Harrison
a reward Of L5000 sterling at once, and a little later L10,000 more, from
Parliament.
While inventors were busy with the problem of accurate chronometers,
however, another instrument for taking longitude at sea had been invented.
This was the reflecting quadrant, or sextant, as the improved instrument is
now called, invented by John Hadley in 1731, and independently by
Thomas Godfrey, a poor glazier of Philadelphia, in 1730. Godfrey's
invention, which was constructed on the same principle as that of the
Hadley instrument, was not generally recognized until two years after
Hadley's discovery, although the instrument was finished and actually in use
on a sea-voyage some months before Hadley reported his invention. The
principle of the sextant, however, seems to have been known to Newton,
who constructed an instrument not very unlike that of Hadley; but this
invention was lost sight of until several years after the philosopher's death
and some time after Hadley's invention.
The introduction of the sextant greatly simplified taking reckonings at
sea as well as facilitating taking the correct longitude of distant places.

Before that time the mariner was obliged to depend upon his compass, a
cross-staff, or an astrolabe, a table of the sun's declination and a correction
for the altitude of the polestar, and very inadequate and incorrect charts.
Such were the instruments used by Columbus and Vasco da Gama and their
immediate successors.
During the Newtonian period the microscopes generally in use were
those constructed of simple lenses, for although compound microscopes
were known, the difficulties of correcting aberration had not been
surmounted, and a much clearer field was given by the simple instrument.
The results obtained by the use of such instruments, however, were very
satisfactory in many ways. By referring to certain plates in this volume,
which reproduce illustrations from Robert Hooke's work on the microscope,
it will be seen that quite a high degree of effectiveness had been attained.
And it should be recalled that Antony von Leeuwenhoek, whose death took
place shortly before Newton's, had discovered such micro-organisms as
bacteria, had seen the blood corpuscles in circulation, and examined and
described other microscopic structures of the body.

XIV. PROGRESS IN ELECTRICITY FROM
GILBERT AND VON GUERICKE TO
FRANKLIN
We have seen how Gilbert, by his experiments with magnets, gave an
impetus to the study of magnetism and electricity. Gilbert himself
demonstrated some facts and advanced some theories, but the system of
general laws was to come later. To this end the discovery of electrical
repulsion, as well as attraction, by Von Guericke, with his sulphur ball, was
a step forward; but something like a century passed after Gilbert's beginning
before anything of much importance was done in the field of electricity.
In 1705, however, Francis Hauksbee began a series of experiments that
resulted in some startling demonstrations. For many years it had been
observed that a peculiar light was seen sometimes in the mercurial
barometer, but Hauksbee and the other scientific investigators supposed the
radiance to be due to the mercury in a vacuum, brought about, perhaps, by
some agitation. That this light might have any connection with electricity
did not, at first, occur to Hauksbee any more than it had to his predecessors.
The problem that interested him was whether the vacuum in the tube of the
barometer was essential to the light; and in experimenting to determine this,
he invented his "mercurial fountain." Having exhausted the air in a receiver
containing some mercury, he found that by allowing air to rush through the
mercury the metal became a jet thrown in all directions against the sides of
the vessel, making a great, flaming shower, "like flashes of lightning," as he
said. But it seemed to him that there was a difference between this light and
the glow noted in the barometer. This was a bright light, whereas the
barometer light was only a glow. Pondering over this, Hauksbee tried
various experiments, revolving pieces of amber, flint, steel, and other
substances in his exhausted air-pump receiver, with negative, or
unsatisfactory, results. Finally, it occurred to him to revolve an exhausted
glass tube itself. Mounting such a globe of glass on an axis so that it could
be revolved rapidly by a belt running on a large wheel, he found that by
holding his fingers against the whirling globe a purplish glow appeared,

giving sufficient light so that coarse print could be read, and the walls of a
dark room sensibly lightened several feet away. As air was admitted to the
globe the light gradually diminished, and it seemed to him that this
diminished glow was very similar in appearance to the pale light seen in the
mercurial barometer. Could it be that it was the glass, and not the mercury,
that caused it? Going to a barometer he proceeded to rub the glass above the
column of mercury over the vacuum, without disturbing the mercury, when,
to his astonishment, the same faint light, to all appearances identical with
the glow seen in the whirling globe, was produced.
Turning these demonstrations over in his mind, he recalled the well-
known fact that rubbed glass attracted bits of paper, leaf-brass, and other
light substances, and that this phenomenon was supposed to be electrical.
This led him finally to determine the hitherto unsuspected fact, that the
glow in the barometer was electrical as was also the glow seen in his
whirling globe. Continuing his investigations, he soon discovered that solid
glass rods when rubbed produced the same effects as the tube. By mere
chance, happening to hold a rubbed tube to his cheek, he felt the effect of
electricity upon the skin like "a number of fine, limber hairs," and this
suggested to him that, since the mysterious manifestation was so plain, it
could be made to show its effects upon various substances. Suspending
some woollen threads over the whirling glass cylinder, he found that as
soon as he touched the glass with his hands the threads, which were waved
about by the wind of the revolution, suddenly straightened themselves in a
peculiar manner, and stood in a radical position, pointing to the axis of the
cylinder.
Encouraged by these successes, he continued his experiments with
breathless expectancy, and soon made another important discovery, that of
"induction," although the real significance of this discovery was not
appreciated by him or, for that matter, by any one else for several
generations following. This discovery was made by placing two revolving
cylinders within an inch of each other, one with the air exhausted and the
other unexhausted. Placing his hand on the unexhausted tube caused the
light to appear not only upon it, but on the other tube as well. A little later
he discovered that it is not necessary to whirl the exhausted tube to produce
this effect, but simply to place it in close proximity to the other whirling
cylinder.

These demonstrations of Hauksbee attracted wide attention and gave an
impetus to investigators in the field of electricity; but still no great advance
was made for something like a quarter of a century. Possibly the energies of
the scientists were exhausted for the moment in exploring the new fields
thrown open to investigation by the colossal work of Newton.
THE EXPERIMENTS OF STEPHEN GRAY
In 1729 Stephen Gray (died in 1736), an eccentric and irascible old
pensioner of the Charter House in London, undertook some investigations
along lines similar to those of Hauksbee. While experimenting with a glass
tube for producing electricity, as Hauksbee had done, he noticed that the
corks with which he had stopped the ends of the tube to exclude the dust,
seemed to attract bits of paper and leaf-brass as well as the glass itself. He
surmised at once that this mysterious electricity, or "virtue," as it was
called, might be transmitted through other substances as it seemed to be
through glass.
"Having by me an ivory ball of about one and three-tenths of an inch in
diameter," he writes, "with a hole through it, this I fixed upon a fir-stick
about four inches long, thrusting the other end into the cork, and upon
rubbing the tube found that the ball attracted and repelled the feather with
more vigor than the cork had done, repeating its attractions and repulsions
for many times together. I then fixed the ball on longer sticks, first upon one
of eight inches, and afterwards upon one of twenty-four inches long, and
found the effect the same. Then I made use of iron, and then brass wire, to
fix the ball on, inserting the other end of the wire in the cork, as before, and
found that the attraction was the same as when the fir-sticks were made use
of, and that when the feather was held over against any part of the wire it
was attracted by it; but though it was then nearer the tube, yet its attraction
was not so strong as that of the ball. When the wire of two or three feet long
was used, its vibrations, caused by the rubbing of the tube, made it
somewhat troublesome to be managed. This put me to thinking whether, if
the ball was hung by a pack-thread and suspended by a loop on the tube, the
electricity would not be carried down the line to the ball; I found it to
succeed accordingly; for upon suspending the ball on the tube by a pack-
thread about three feet long, when the tube had been excited by rubbing, the
ivory ball attracted and repelled the leaf-brass over which it was held as

freely as it had done when it was suspended on sticks or wire, as did also a
ball of cork, and another of lead that weighed one pound and a quarter."
Gray next attempted to determine what other bodies would attract the bits
of paper, and for this purpose he tried coins, pieces of metal, and even a tea-
kettle, "both empty and filled with hot or cold water"; but he found that the
attractive power appeared to be the same regardless of the substance used.
"I next proceeded," he continues, "to try at what greater distances the
electric virtues might be carried, and having by me a hollow walking-cane,
which I suppose was part of a fishing-rod, two feet seven inches long, I cut
the great end of it to fit into the bore of the tube, into which it went about
five inches; then when the cane was put into the end of the tube, and this
excited, the cane drew the leaf-brass to the height of more than two inches,
as did also the ivory ball, when by a cork and stick it had been fixed to the
end of the cane.... With several pieces of Spanish cane and fir-sticks I
afterwards made a rod, which, together with the tube, was somewhat more
than eighteen feet long, which was the greatest length I could conveniently
use in my chamber, and found the attraction very nearly, if not altogether, as
strong as when the ball was placed on the shorter rods."
This experiment exhausted the capacity of his small room, but on going
to the country a little later he was able to continue his experiments. "To a
pole of eighteen feet there was tied a line of thirty-four feet in length, so
that the pole and line together were fifty-two feet. With the pole and tube I
stood in the balcony, the assistant below in the court, where he held the
board with the leaf-brass on it. Then the tube being excited, as usual, the
electric virtue passed from the tube up the pole and down the line to the
ivory ball, which attracted the leaf-brass, and as the ball passed over it in its
vibrations the leaf-brass would follow it till it was carried off the board."
Gray next attempted to send the electricity over a line suspended
horizontally. To do this he suspended the pack-thread by pieces of string
looped over nails driven into beams for that purpose. But when thus
suspended he found that the ivory ball no longer excited the leaf-brass, and
he guessed correctly that the explanation of this lay in the fact that "when
the electric virtue came to the loop that was suspended on the beam it went
up the same to the beam," none of it reaching the ball. As we shall see from
what follows, however, Gray had not as yet determined that certain
substances will conduct electricity while others will not. But by a lucky

accident he made the discovery that silk, for example, was a poor
conductor, and could be turned to account in insulating the conducting-cord.
A certain Mr. Wheler had become much interested in the old pensioner
and his work, and, as a guest at the Wheler house, Gray had been repeating
some of his former experiments with the fishing-rod, line, and ivory ball.
He had finally exhausted the heights from which these experiments could
be made by climbing to the clock-tower and exciting bits of leaf-brass on
the ground below.
"As we had no greater heights here," he says, "Mr. Wheler was desirous
to try whether we could not carry the electric virtue horizontally. I then told
him of the attempt I had made with that design, but without success, telling
him the method and materials made use of, as mentioned above. He then
proposed a silk line to support the line by which the electric virtue was to
pass. I told him it might do better upon account of its smallness; so that
there would be less virtue carried from the line of communication.
"The first experiment was made in the matted gallery, July 2, 1729, about
ten in the morning. About four feet from the end of the gallery there was a
cross line that was fixed by its ends to each side of the gallery by two nails;
the middle part of the line was silk, the rest at each end pack-thread; then
the line to which the ivory ball was hung and by which the electric virtue
was to be conveyed to it from the tube, being eighty and one-half feet in
length, was laid on the cross silk line, so that the ball hung about nine feet
below it. Then the other end of the line was by a loop suspended on the
glass cane, and the leaf-brass held under the ball on a piece of white paper;
when, the tube being rubbed, the ball attracted the leaf-brass, and kept it
suspended on it for some time."
This experiment succeeded so well that the string was lengthened until it
was some two hundred and ninety-three feet long; and still the attractive
force continued, apparently as strong as ever. On lengthening the string still
more, however, the extra weight proved too much for the strength of the silk
suspending-thread. "Upon this," says Gray, "having brought with me both
brass and iron wire, instead of the silk we put up small iron wire; but this
was too weak to bear the weight of the line. We then took brass wire of a
somewhat larger size than that of iron. This supported our line of
communication; but though the tube was well rubbed, yet there was not the
least motion or attraction given by the ball, neither with the great tube,

which we made use of when we found the small solid cane to be ineffectual;
by which we were now convinced that the success we had before depended
upon the lines that supported the line of communication being silk, and not
upon their being small, as before trial I had imagined it might be; the same
effect happening here as it did when the line that is to convey the electric
virtue is supported by pack-thread."
Soon after this Gray and his host suspended a pack-thread six hundred
and sixty-six feet long on poles across a field, these poles being slightly
inclined so that the thread could be suspended from the top by small silk
cords, thus securing the necessary insulation. This pack-thread line,
suspended upon poles along which Gray was able to transmit the electricity,
is very suggestive of the modern telegraph, but the idea of signalling or
making use of it for communicating in any way seems not to have occurred
to any one at that time. Even the successors of Gray who constructed lines
some thousands of feet long made no attempt to use them for anything but
experimental purposes—simply to test the distances that the current could
be sent. Nevertheless, Gray should probably be credited with the discovery
of two of the most important properties of electricity—that it can be
conducted and insulated, although, as we have seen, Gilbert and Von
Guericke had an inkling of both these properties.
EXPERIMENTS OF CISTERNAY DUFAY
So far England had produced the two foremost workers in electricity. It
was now France's turn to take a hand, and, through the efforts of Charles
Francois de Cisternay Dufay, to advance the science of electricity very
materially. Dufay was a highly educated savant, who had been soldier and
diplomat betimes, but whose versatility and ability as a scientist is shown
by the fact that he was the only man who had ever contributed to the annals
of the academy investigations in every one of the six subjects admitted by
that institution as worthy of recognition. Dufay upheld his reputation in this
new field of science, making many discoveries and correcting many
mistakes of former observers. In this work also he proved himself a great
diplomat by remaining on terms of intimate friendship with Dr. Gray—a
thing that few people were able to do.
Almost his first step was to overthrow the belief that certain bodies are
"electrics" and others "non-electrics"—that is, that some substances when
rubbed show certain peculiarities in attracting pieces of paper and foil

which others do not. Dufay proved that all bodies possess this quality in a
certain degree.
"I have found that all bodies (metallic, soft, or fluid ones excepted)," he
says, "may be made electric by first heating them more or less and then
rubbing them on any sort of cloth. So that all kinds of stones, as well
precious as common, all kinds of wood, and, in general, everything that I
have made trial of, became electric by beating and rubbing, except such
bodies as grow soft by beat, as the gums, which dissolve in water, glue, and
such like substances. 'Tis also to be remarked that the hardest stones or
marbles require more chafing or heating than others, and that the same rule
obtains with regard to the woods; so that box, lignum vitae, and such others
must be chafed almost to the degree of browning, whereas fir, lime-tree, and
cork require but a moderate heat.
"Having read in one of Mr. Gray's letters that water may be made
electrical by holding the excited glass tube near it (a dish of water being
fixed to a stand and that set on a plate of glass, or on the brim of a drinking-
glass, previously chafed, or otherwise warmed), I have found, upon trial,
that the same thing happened to all bodies without exception, whether solid
or fluid, and that for that purpose 'twas sufficient to set them on a glass
stand slightly warmed, or only dried, and then by bringing the tube near
them they immediately became electrical. I made this experiment with ice,
with a lighted wood-coal, and with everything that came into my mind; and
I constantly remarked that such bodies of themselves as were least electrical
had the greatest degree of electricity communicated to them at the approval
of the glass tube."
His next important discovery was that colors had nothing to do with the
conduction of electricity. "Mr. Gray says, towards the end of one of his
letters," he writes, "that bodies attract more or less according to their colors.
This led me to make several very singular experiments. I took nine silk
ribbons of equal size, one white, one black, and the other seven of the seven
primitive colors, and having hung them all in order in the same line, and
then bringing the tube near them, the black one was first attracted, the white
one next, and others in order successively to the red one, which was
attracted least, and the last of them all. I afterwards cut out nine square
pieces of gauze of the same colors with the ribbons, and having put them
one after another on a hoop of wood, with leaf-gold under them, the leaf-

gold was attracted through all the colored pieces of gauze, but not through
the white or black. This inclined me first to think that colors contribute
much to electricity, but three experiments convinced me to the contrary. The
first, that by warming the pieces of gauze neither the black nor white pieces
obstructed the action of the electrical tube more than those of the other
colors. In like manner, the ribbons being warmed, the black and white are
not more strongly attracted than the rest. The second is, the gauzes and
ribbons being wetted, the ribbons are all attracted equally, and all the pieces
of gauze equally intercept the action of electric bodies. The third is, that the
colors of a prism being thrown on a white gauze, there appear no
differences of attraction. Whence it proceeds that this difference proceeds,
not from the color, as a color, but from the substances that are employed in
the dyeing. For when I colored ribbons by rubbing them with charcoal,
carmine, and such other substances, the differences no longer proved the
same."
In connection with his experiments with his thread suspended on glass
poles, Dufay noted that a certain amount of the current is lost, being given
off to the surrounding air. He recommended, therefore, that the cords
experimented with be wrapped with some non-conductor—that it should be
"insulated" ("isolee"), as he said, first making use of this term.
DUFAY DISCOVERS VITREOUS AND RESINOUS ELECTRICITY
It has been shown in an earlier chapter how Von Guericke discovered that
light substances like feathers, after being attracted to the sulphur-ball
electric-machine, were repelled by it until they touched some object. Von
Guericke noted this, but failed to explain it satisfactorily. Dufay, repeating
Von Guericke's experiments, found that if, while the excited tube or sulphur
ball is driving the repelled feather before it, the ball be touched or rubbed
anew, the feather comes to it again, and is repelled alternately, as, the hand
touches the ball, or is withdrawn. From this he concluded that electrified
bodies first attract bodies not electrified, "charge" them with electricity, and
then repel them, the body so charged not being attracted again until it has
discharged its electricity by touching something.
"On making the experiment related by Otto von Guericke," he says,
"which consists in making a ball of sulphur rendered electrical to repel a
down feather, I perceived that the same effects were produced not only by
the tube, but by all electric bodies whatsoever, and I discovered that which

accounts for a great part of the irregularities and, if I may use the term, of
the caprices that seem to accompany most of the experiments on electricity.
This principle is that electric bodies attract all that are not so, and repel
them as soon as they are become electric by the vicinity or contact of the
electric body. Thus gold-leaf is first attracted by the tube, and acquires an
electricity by approaching it, and of consequence is immediately repelled by
it. Nor is it reattracted while it retains its electric quality. But if while it is
thus sustained in the air it chance to light on some other body, it straightway
loses its electricity, and in consequence is reattracted by the tube, which,
after having given it a new electricity, repels it a second time, which
continues as long as the tube keeps its electricity. Upon applying this
principle to the various experiments of electricity, one will be surprised at
the number of obscure and puzzling facts that it clears up. For Mr.
Hauksbee's famous experiment of the glass globe, in which silk threads are
put, is a necessary consequence of it. When these threads are arranged in
the form of rays by the electricity of the sides of the globe, if the finger be
put near the outside of the globe the silk threads within fly from it, as is
well known, which happens only because the finger or any other body
applied near the glass globe is thereby rendered electrical, and consequently
repels the silk threads which are endowed with the same quality. With a
little reflection we may in the same manner account for most of the other
phenomena, and which seem inexplicable without attending to this
principle.
"Chance has thrown in my way another principle, more universal and
remarkable than the preceding one, and which throws a new light on the
subject of electricity. This principle is that there are two distinct
electricities, very different from each other, one of which I call vitreous
electricity and the other resinous electricity. The first is that of glass, rock-
crystal, precious stones, hair of animals, wool, and many other bodies. The
second is that of amber, copal, gumsack, silk thread, paper, and a number of
other substances. The characteristic of these two electricities is that a body
of the vitreous electricity, for example, repels all such as are of the same
electricity, and on the contrary attracts all those of the resinous electricity;
so that the tube, made electrical, will repel glass, crystal, hair of animals,
etc., when rendered electric, and will attract silk thread, paper, etc., though
rendered electrical likewise. Amber, on the contrary, will attract electric
glass and other substances of the same class, and will repel gum-sack,

copal, silk thread, etc. Two silk ribbons rendered electrical will repel each
other; two woollen threads will do the like; but a woollen thread and a
silken thread will mutually attract each other. This principle very naturally
explains why the ends of threads of silk or wool recede from each other, in
the form of pencil or broom, when they have acquired an electric quality.
From this principle one may with the same ease deduce the explanation of a
great number of other phenomena; and it is probable that this truth will lead
us to the further discovery of many other things.
"In order to know immediately to which of the two classes of electrics
belongs any body whatsoever, one need only render electric a silk thread,
which is known to be of the resinuous electricity, and see whether that body,
rendered electrical, attracts or repels it. If it attracts it, it is certainly of the
kind of electricity which I call VITREOUS; if, on the contrary, it repels it, it
is of the same kind of electricity with the silk—that is, of the RESINOUS. I
have likewise observed that communicated electricity retains the same
properties; for if a ball of ivory or wood be set on a glass stand, and this ball
be rendered electric by the tube, it will repel such substances as the tube
repels; but if it be rendered electric by applying a cylinder of gum-sack near
it, it will produce quite contrary effects—namely, precisely the same as
gum-sack would produce. In order to succeed in these experiments, it is
requisite that the two bodies which are put near each other, to find out the
nature of their electricity, be rendered as electrical as possible, for if one of
them was not at all or but weakly electrical, it would be attracted by the
other, though it be of that sort that should naturally be repelled by it. But the
experiment will always succeed perfectly well if both bodies are sufficiently
electrical."(1)
As we now know, Dufay was wrong in supposing that there were two
different kinds of electricity, vitreous and resinous. A little later the matter
was explained by calling one "positive" electricity and the other "negative,"
and it was believed that certain substances produced only the one kind
peculiar to that particular substance. We shall see presently, however, that
some twenty years later an English scientist dispelled this illusion by
producing both positive (or vitreous) and negative (or resinous) electricity
on the same tube of glass at the same time.
After the death of Dufay his work was continued by his fellow-
countryman Dr. Joseph Desaguliers, who was the first experimenter to

electrify running water, and who was probably the first to suggest that
clouds might be electrified bodies. But about, this time—that is, just before
the middle of the eighteenth century—the field of greatest experimental
activity was transferred to Germany, although both England and France
were still active. The two German philosophers who accomplished most at
this time were Christian August Hansen and George Matthias Bose, both
professors in Leipsic. Both seem to have conceived the idea, simultaneously
and independently, of generating electricity by revolving globes run by belt
and wheel in much the same manner as the apparatus of Hauksbee.
With such machines it was possible to generate a much greater amount of
electricity than Dufay had been able to do with the rubbed tube, and so
equipped, the two German professors were able to generate electric sparks
and jets of fire in a most startling manner. Bose in particular had a love for
the spectacular, which he turned to account with his new electrical machine
upon many occasions. On one of these occasions he prepared an elaborate
dinner, to which a large number of distinguished guests were invited.
Before the arrival of the company, however, Bose insulated the great
banquet-table on cakes of pitch, and then connected it with a huge electrical
machine concealed in another room. All being ready, and the guests in their
places about to be seated, Bose gave a secret signal for starting this
machine, when, to the astonishment of the party, flames of fire shot from
flowers, dishes, and viands, giving a most startling but beautiful display.
To add still further to the astonishment of his guests, Bose then presented
a beautiful young lady, to whom each of the young men of the party was
introduced. In some mysterious manner she was insulated and connected
with the concealed electrical machine, so that as each gallant touched her
fingertips he received an electric shock that "made him reel." Not content
with this, the host invited the young men to kiss the beautiful maid. But
those who were bold enough to attempt it received an electric shock that
nearly "knocked their teeth out," as the professor tells it.
LUDOLFF'S EXPERIMENT WITH THE ELECTRIC SPARK
But Bose was only one of several German scientists who were making
elaborate experiments. While Bose was constructing and experimenting
with his huge machine, another German, Christian Friedrich Ludolff,
demonstrated that electric sparks are actual fire—a fact long suspected but
hitherto unproved. Ludolff's discovery, as it chanced, was made in the

lecture-hall of the reorganized Academy of Sciences at Berlin, before an
audience of scientists and great personages, at the opening lecture in 1744.
In the course of this lecture on electricity, during which some of the well-
known manifestations of electricity were being shown, it occurred to
Ludolff to attempt to ignite some inflammable fluid by projecting an
electric spark upon its surface with a glass rod. This idea was suggested to
him while performing the familiar experiment of producing a spark on the
surface of a bowl of water by touching it with a charged glass rod. He
announced to his audience the experiment he was about to attempt, and
having warmed a spoonful of sulphuric ether, he touched its surface with
the glass rod, causing it to burst into flame. This experiment left no room
for doubt that the electric spark was actual fire.
As soon as this experiment of Ludolff's was made known to Bose, he
immediately claimed that he had previously made similar demonstrations
on various inflammable substances, both liquid and solid; and it seems
highly probable that he had done so, as he was constantly experimenting
with the sparks, and must almost certainly have set certain substances
ablaze by accident, if not by intent. At all events, he carried on a series of
experiments along this line to good purpose, finally succeeding in
exploding gun-powder, and so making the first forerunner of the electric
fuses now so universally used in blasting, firing cannon, and other similar
purposes. It was Bose also who, observing some of the peculiar
manifestations in electrified tubes, and noticing their resemblance to
"northern lights," was one of the first, if not the first, to suggest that the
aurora borealis is of electric origin.
These spectacular demonstrations had the effect of calling public
attention to the fact that electricity is a most wonderful and mysterious
thing, to say the least, and kept both scientists and laymen agog with
expectancy. Bose himself was aflame with excitement, and so determined in
his efforts to produce still stronger electric currents, that he sacrificed the
tube of his twenty-foot telescope for the construction of a mammoth
electrical machine. With this great machine a discharge of electricity was
generated powerful enough to wound the skin when it happened to strike it.
Until this time electricity had been little more than a plaything of the
scientists—or, at least, no practical use had been made of it. As it was a
practising physician, Gilbert, who first laid the foundation for

experimenting with the new substance, so again it was a medical man who
first attempted to put it to practical use, and that in the field of his
profession. Gottlieb Kruger, a professor of medicine at Halle in 1743,
suggested that electricity might be of use in some branches of medicine;
and the year following Christian Gottlieb Kratzenstein made a first
experiment to determine the effects of electricity upon the body. He found
that "the action of the heart was accelerated, the circulation increased, and
that muscles were made to contract by the discharge": and he began at once
administering electricity in the treatment of certain diseases. He found that
it acted beneficially in rheumatic affections, and that it was particularly
useful in certain nervous diseases, such as palsies. This was over a century
ago, and to-day about the most important use made of the particular kind of
electricity with which he experimented (the static, or frictional) is for the
treatment of diseases affecting the nervous system.
By the middle of the century a perfect mania for making electrical
machines had spread over Europe, and the whirling, hand-rubbed globes
were gradually replaced by great cylinders rubbed by woollen cloths or
pads, and generating an "enormous power of electricity." These cylinders
were run by belts and foot-treadles, and gave a more powerful, constant,
and satisfactory current than known heretofore. While making experiments
with one of these machines, Johann Heinrichs Winkler attempted to
measure the speed at which electricity travels. To do this he extended a cord
suspended on silk threads, with the end attached to the machine and the end
which was to attract the bits of gold-leaf near enough together so that the
operator could watch and measure the interval of time that elapsed between
the starting of the current along the cord and its attracting the gold-leaf. The
length of the cord used in this experiment was only a little over a hundred
feet, and this was, of course, entirely inadequate, the current travelling that
space apparently instantaneously.
The improved method of generating electricity that had come into
general use made several of the scientists again turn their attention more
particularly to attempt putting it to some practical account. They were
stimulated to these efforts by the constant reproaches that were beginning to
be heard on all sides that electricity was merely a "philosopher's plaything."
One of the first to succeed in inventing something that approached a
practical mechanical contrivance was Andrew Gordon, a Scotch
Benedictine monk. He invented an electric bell which would ring

automatically, and a little "motor," if it may be so called. And while neither
of these inventions were of any practical importance in themselves, they
were attempts in the right direction, and were the first ancestors of modern
electric bells and motors, although the principle upon which they worked
was entirely different from modern electrical machines. The motor was
simply a wheel with several protruding metal points around its rim. These
points were arranged to receive an electrical discharge from a frictional
machine, the discharge causing the wheel to rotate. There was very little
force given to this rotation, however, not enough, in fact, to make it
possible to more than barely turn the wheel itself. Two more great
discoveries, galvanism and electro-magnetic induction, were necessary
before the practical motor became possible.
The sober Gordon had a taste for the spectacular almost equal to that of
Bose. It was he who ignited a bowl of alcohol by turning a stream of
electrified water upon it, thus presenting the seeming paradox of fire
produced by a stream of water. Gordon also demonstrated the power of the
electrical discharge by killing small birds and animals at a distance of two
hundred ells, the electricity being conveyed that distance through small
wires.
THE LEYDEN JAR DISCOVERED
As yet no one had discovered that electricity could be stored, or
generated in any way other than by some friction device. But very soon two
experimenters, Dean von Kleist, of Camin, Pomerania, and Pieter van
Musschenbroek, the famous teacher of Leyden, apparently independently,
made the discovery of what has been known ever since as the Leyden jar.
And although Musschenbroek is sometimes credited with being the
discoverer, there can be no doubt that Von Kleist's discovery antedated his
by a few months at least.
Von Kleist found that by a device made of a narrow-necked bottle
containing alcohol or mercury, into which an iron nail was inserted, he was
able to retain the charge of electricity, after electrifying this apparatus with
the frictional machine. He made also a similar device, more closely
resembling the modern Leyden jar, from a thermometer tube partly filled
with water and a wire tipped with a ball of lead. With these devices he
found that he could retain the charge of electricity for several hours, and
could produce the usual electrical manifestations, even to igniting spirits,

quite as well as with the frictional machine. These experiments were first
made in October, 1745, and after a month of further experimenting, Von
Kleist sent the following account of them to several of the leading
scientists, among others, Dr. Lieberkuhn, in Berlin, and Dr. Kruger, of
Halle.
"When a nail, or a piece of thick brass wire, is put into a small
apothecary's phial and electrified, remarkable effects follow; but the phial
must be very dry, or warm. I commonly rub it over beforehand with a finger
on which I put some pounded chalk. If a little mercury or a few drops of
spirit of wine be put into it, the experiment succeeds better. As soon as this
phial and nail are removed from the electrifying-glass, or the prime
conductor, to which it has been exposed, is taken away, it throws out a
pencil of flame so long that, with this burning machine in my hand, I have
taken above sixty steps in walking about my room. When it is electrified
strongly, I can take it into another room and there fire spirits of wine with it.
If while it is electrifying I put my finger, or a piece of gold which I hold in
my hand, to the nail, I receive a shock which stuns my arms and shoulders.
"A tin tube, or a man, placed upon electrics, is electrified much stronger
by this means than in the common way. When I present this phial and nail
to a tin tube, which I have, fifteen feet long, nothing but experience can
make a person believe how strongly it is electrified. I am persuaded," he
adds, "that in this manner Mr. Bose would not have taken a second
electrical kiss. Two thin glasses have been broken by the shock of it. It
appears to me very extraordinary, that when this phial and nail are in
contact with either conducting or non-conducting matter, the strong shock
does not follow. I have cemented it to wood, metal, glass, sealing-wax, etc.,
when I have electrified without any great effect. The human body, therefore,
must contribute something to it. This opinion is confirmed by my observing
that unless I hold the phial in my hand I cannot fire spirits of wine with it."
(2)
But it seems that none of the men who saw this account were able to
repeat the experiment and produce the effects claimed by Von Kleist, and
probably for this reason the discovery of the obscure Pomeranian was for a
time lost sight of.
Musschenbroek's discovery was made within a short time after Von
Kleist's—in fact, only a matter of about two months later. But the difference

in the reputations of the two discoverers insured a very different reception
for their discoveries. Musschenbroek was one of the foremost teachers of
Europe, and so widely known that the great universities vied with each
other, and kings were bidding, for his services. Naturally, any discovery
made by such a famous person would soon be heralded from one end of
Europe to the other. And so when this professor of Leyden made his
discovery, the apparatus came to be called the "Leyden jar," for want of a
better name. There can be little doubt that Musschenbroek made his
discovery entirely independently of any knowledge of Von Kleist's, or, for
that matter, without ever having heard of the Pomeranian, and his actions in
the matter are entirely honorable.
His discovery was the result of an accident. While experimenting to
determine the strength of electricity he suspended a gun-barrel, which he
charged with electricity from a revolving glass globe. From the end of the
gun-barrel opposite the globe was a brass wire, which extended into a glass
jar partly filled with water. Musschenbroek held in one hand this jar, while
with the other he attempted to draw sparks from the barrel. Suddenly he
received a shock in the hand holding the jar, that "shook him like a stroke of
lightning," and for a moment made him believe that "he was done for."
Continuing his experiments, nevertheless, he found that if the jar were
placed on a piece of metal on the table, a shock would be received by
touching this piece of metal with one hand and touching the wire with the
other—that is, a path was made for the electrical discharge through the
body. This was practically the same experiment as made by Von Kleist with
his bottle and nail, but carried one step farther, as it showed that the "jar"
need not necessarily be held in the hand, as believed by Von Kleist. Further
experiments, continued by many philosophers at the time, revealed what
Von Kleist had already pointed out, that the electrified jar remained charged
for some time.
Soon after this Daniel Gralath, wishing to obtain stronger discharges than
could be had from a single Leyden jar, conceived the idea of combining
several jars, thus for the first time grouping the generators in a "battery"
which produced a discharge strong enough to kill birds and small animals.
He also attempted to measure the strength of the discharges, but soon gave
it up in despair, and the solution of this problem was left for late nineteenth-
century scientists.

The advent of the Leyden jar, which made it possible to produce strong
electrical discharges from a small and comparatively simple device, was
followed by more spectacular demonstrations of various kinds all over
Europe. These exhibitions aroused the interest of the kings and noblemen,
so that electricity no longer remained a "plaything of the philosophers"
alone, but of kings as well. A favorite demonstration was that of sending the
electrical discharge through long lines of soldiers linked together by pieces
of wire, the discharge causing them to "spring into the air simultaneously"
in a most astonishing manner. A certain monk in Paris prepared a most
elaborate series of demonstrations for the amusement of the king, among
other things linking together an entire regiment of nine hundred men,
causing them to perform simultaneous springs and contortions in a manner
most amusing to the royal guests. But not all the experiments being made
were of a purely spectacular character, although most of them accomplished
little except in a negative way. The famous Abbe Nollet, for example,
combined useful experiments with spectacular demonstrations, thus keeping
up popular interest while aiding the cause of scientific electricity.
WILLIAM WATSON
Naturally, the new discoveries made necessary a new nomenclature, new
words and electrical terms being constantly employed by the various writers
of that day. Among these writers was the English scientist William Watson,
who was not only a most prolific writer but a tireless investigator. Many of
the words coined by him are now obsolete, but one at least, "circuit," still
remains in use.
In 1746, a French scientist, Louis Guillaume le Monnier, bad made a
circuit including metal and water by laying a chain half-way around the
edge of a pond, a man at either end holding it. One of these men dipped his
free hand in the water, the other presenting a Leyden jar to a rod suspended
on a cork float on the water, both men receiving a shock simultaneously.
Watson, a year later, attempted the same experiment on a larger scale. He
laid a wire about twelve hundred feet long across Westminster Bridge over
the Thames, bringing the ends to the water's edge on the opposite banks, a
man at one end holding the wire and touching the water. A second man on
the opposite side held the wire and a Leyden jar; and a third touched the jar
with one hand, while with the other he grasped a wire that extended into the
river. In this way they not only received the shock, but fired alcohol as

readily across the stream as could be done in the laboratory. In this
experiment Watson discovered the superiority of wire over chain as a
conductor, rightly ascribing this superiority to the continuity of the metal.
Watson continued making similar experiments over longer watercourses,
some of them as long as eight thousand feet, and while engaged in making
one of these he made the discovery so essential to later inventions, that the
earth could be used as part of the circuit in the same manner as bodies of
water. Lengthening his wires he continued his experiments until a circuit of
four miles was made, and still the electricity seemed to traverse the course
instantaneously, and with apparently undiminished force, if the insulation
was perfect.
BENJAMIN FRANKLIN
Watson's writings now carried the field of active discovery across the
Atlantic, and for the first time an American scientist appeared—a scientist
who not only rivalled, but excelled, his European contemporaries. Benjamin
Franklin, of Philadelphia, coming into possession of some of Watson's
books, became so interested in the experiments described in them that he
began at once experimenting with electricity. In Watson's book were given
directions for making various experiments, and these assisted Franklin in
repeating the old experiments, and eventually adding new ones. Associated
with Franklin, and equally interested and enthusiastic, if not equally
successful in making discoveries, were three other men, Thomas
Hopkinson, Philip Sing, and Ebenezer Kinnersley. These men worked
together constantly, although it appears to have been Franklin who made
independently the important discoveries, and formulated the famous
Franklinian theory.
Working steadily, and keeping constantly in touch with the progress of
the European investigators, Franklin soon made some experiments which he
thought demonstrated some hitherto unknown phases of electrical
manifestation. This was the effect of pointed bodies "in DRAWING OFF
and THROWING OFF the electrical fire." In his description of this
phenomenon, Franklin writes:
"Place an iron shot of three or four inches diameter on the mouth of a
clean, dry, glass bottle. By a fine silken thread from the ceiling right over
the mouth of the bottle, suspend a small cork ball, about the bigness of a
marble; the thread of such a length that the cork ball may rest against the

side of the shot. Electrify the shot, and the ball will be repelled to the
distance of four or five inches, more or less, according to the quantity of
electricity. When in this state, if you present to the shot the point of a long,
slender shaft-bodkin, at six or eight inches distance, the repellency is
instantly destroyed, and the cork flies to the shot. A blunt body must be
brought within an inch, and draw a spark, to produce the same effect.
"To prove that the electrical fire is DRAWN OFF by the point, if you take
the blade of the bodkin out of the wooden handle and fix it in a stick of
sealing-wax, and then present it at the distance aforesaid, or if you bring it
very near, no such effect follows; but sliding one finger along the wax till
you touch the blade, and the ball flies to the shot immediately. If you
present the point in the dark you will see, sometimes at a foot distance, and
more, a light gather upon it like that of a fire-fly or glow-worm; the less
sharp the point, the nearer you must bring it to observe the light; and at
whatever distance you see the light, you may draw off the electrical fire and
destroy the repellency. If a cork ball so suspended be repelled by the tube,
and a point be presented quick to it, though at a considerable distance, 'tis
surprising to see how suddenly it flies back to the tube. Points of wood will
do as well as those of iron, provided the wood is not dry; for perfectly dry
wood will no more conduct electricity than sealing-wax.
"To show that points will THROW OFF as well as DRAW OFF the
electrical fire, lay a long, sharp needle upon the shot, and you cannot
electrify the shot so as to make it repel the cork ball. Or fix a needle to the
end of a suspended gun-barrel or iron rod, so as to point beyond it like a
little bayonet, and while it remains there, the gun-barrel or rod cannot, by
applying the tube to the other end, be electrified so as to give a spark, the
fire continually running out silently at the point. In the dark you may see it
make the same appearance as it does in the case before mentioned."(3)
Von Guericke, Hauksbee, and Gray had noticed that pointed bodies
attracted electricity in a peculiar manner, but this demonstration of the
"drawing off" of "electrical fire" was original with Franklin. Original also
was the theory that he now suggested, which had at least the merit of being
thinkable even by non-philosophical minds. It assumes that electricity is
like a fluid, that will flow along conductors and accumulate in proper
receptacles, very much as ordinary fluids do. This conception is probably
entirely incorrect, but nevertheless it is likely to remain a popular one, at

least outside of scientific circles, or until something equally tangible is
substituted.
FRANKLIN'S THEORY OF ELECTRICITY
According to Franklin's theory, electricity exists in all bodies as a
"common stock," and tends to seek and remain in a state of equilibrium, just
as fluids naturally tend to seek a level. But it may, nevertheless, be raised or
lowered, and this equilibrium be thus disturbed. If a body has more
electricity than its normal amount it is said to be POSITIVELY electrified;
but if it has less, it is NEGATIVELY electrified. An over-electrified or
"plus" body tends to give its surplus stock to a body containing the normal
amount; while the "minus" or under-electrified body will draw electricity
from one containing the normal amount.
Working along lines suggested by this theory, Franklin attempted to show
that electricity is not created by friction, but simply collected from its
diversified state, the rubbed glass globe attracting a certain quantity of
"electrical fire," but ever ready to give it up to any body that has less. He
explained the charged Leyden jar by showing that the inner coating of tin-
foil received more than the ordinary quantity of electricity, and in
consequence is POSITIVELY electrified, while the outer coating, having
the ordinary quantity of electricity diminished, is electrified NEGATIVELY.
These studies of the Leyden jar, and the studies of pieces of glass coated
with sheet metal, led Franklin to invent his battery, constructed of eleven
large glass plates coated with sheets of lead. With this machine, after
overcoming some defects, he was able to produce electrical manifestations
of great force—a force that "knew no bounds," as he declared ("except in
the matter of expense and of labor"), and which could be made to exceed
"the greatest know effects of common lightning."
This reference to lightning would seem to show Franklin's belief, even at
that time, that lightning is electricity. Many eminent observers, such as
Hauksbee, Wall, Gray, and Nollet, had noticed the resemblance between
electric sparks and lightning, but none of these had more than surmised that
the two might be identical. In 1746, the surgeon, John Freke, also asserted
his belief in this identity. Winkler, shortly after this time, expressed the
same belief, and, assuming that they were the same, declared that "there is
no proof that they are of different natures"; and still he did not prove that
they were the same nature.

FRANKLIN INVENTS THE LIGHTNING-ROD
Even before Franklin proved conclusively the nature of lightning, his
experiments in drawing off the electric charge with points led to some
practical suggestions which resulted in the invention of the lightning-rod. In
the letter of July, 1750, which he wrote on the subject, he gave careful
instructions as to the way in which these rods might be constructed. In part
Franklin wrote: "May not the knowledge of this power of points be of use to
mankind in preserving houses, churches, ships, etc., from the stroke of
lightning by directing us to fix on the highest parts of the edifices upright
rods of iron made sharp as a needle, and gilt to prevent rusting, and from
the foot of these rods a wire down the outside of the building into the
grounds, or down round one of the shrouds of a ship and down her side till
it reaches the water? Would not these pointed rods probably draw the
electrical fire silently out of a cloud before it came nigh enough to strike,
and thereby secure us from that most sudden and terrible mischief?
"To determine this question, whether the clouds that contain the lightning
are electrified or not, I propose an experiment to be tried where it may be
done conveniently. On the top of some high tower or steeple, place a kind
of sentry-box, big enough to contain a man and an electrical stand. From the
middle of the stand let an iron rod rise and pass, bending out of the door,
and then upright twenty or thirty feet, pointed very sharp at the end. If the
electrical stand be kept clean and dry, a man standing on it when such
clouds are passing low might be electrified and afford sparks, the rod
drawing fire to him from a cloud. If any danger to the man be apprehended
(though I think there would be none), let him stand on the floor of his box
and now and then bring near to the rod the loop of a wire that has one end
fastened to the leads, he holding it by a wax handle; so the sparks, if the rod
is electrified, will strike from the rod to the wire and not effect him."(4)
Not satisfied with all the evidence that he had collected pointing to the
identity of lightning and electricity, he adds one more striking and very
suggestive piece of evidence. Lightning was known sometimes to strike
persons blind without killing them. In experimenting on pigeons and pullets
with his electrical machine, Franklin found that a fowl, when not killed
outright, was sometimes rendered blind. The report of these experiments
were incorporated in this famous letter of the Philadelphia philosopher.

The attitude of the Royal Society towards this clearly stated letter, with
its useful suggestions, must always remain as a blot on the record of this
usually very receptive and liberal-minded body. Far from publishing it or
receiving it at all, they derided the whole matter as too visionary for
discussion by the society. How was it possible that any great scientific
discovery could be made by a self-educated colonial newspaper editor, who
knew nothing of European science except by hearsay, when all the great
scientific minds of Europe had failed to make the discovery? How indeed!
And yet it would seem that if any of the influential members of the learned
society had taken the trouble to read over Franklin's clearly stated letter,
they could hardly have failed to see that his suggestions were worthy of
consideration. But at all events, whether they did or did not matters little.
The fact remains that they refused to consider the paper seriously at the
time; and later on, when its true value became known, were obliged to
acknowledge their error by a tardy report on the already well-known
document.
But if English scientists were cold in their reception of Franklin's theory
and suggestions, the French scientists were not. Buffon, perceiving at once
the importance of some of Franklin's experiments, took steps to have the
famous letter translated into French, and soon not only the savants, but
members of the court and the king himself were intensely interested. Two
scientists, De Lor and D'Alibard, undertook to test the truth of Franklin's
suggestions as to pointed rods "drawing off lightning." In a garden near
Paris, the latter erected a pointed iron rod fifty feet high and an inch in
diameter. As no thunder-clouds appeared for several days, a guard was
stationed, armed with an insulated brass wire, who was directed to test the
iron rods with it in case a storm came on during D'Alibard's absence. The
storm did come on, and the guard, not waiting for his employer's arrival,
seized the wire and touched the rod. Instantly there was a report. Sparks
flew and the guard received such a shock that he thought his time had come.
Believing from his outcry that he was mortally hurt, his friends rushed for a
spiritual adviser, who came running through rain and hail to administer the
last rites; but when he found the guard still alive and uninjured, he turned
his visit to account by testing the rod himself several times, and later
writing a report of his experiments to M. d'Alibard. This scientist at once
reported the affair to the French Academy, remarking that "Franklin's idea
was no longer a conjecture, but a reality."

FRANKLIN PROVES THAT LIGHTNING IS ELECTRICITY
Europe, hitherto somewhat sceptical of Franklin's views, was by this time
convinced of the identity of lightning and electricity. It was now Franklin's
turn to be sceptical. To him the fact that a rod, one hundred feet high,
became electrified during a storm did not necessarily prove that the storm-
clouds were electrified. A rod of that length was not really projected into the
cloud, for even a very low thunder-cloud was more than a hundred feet
above the ground. Irrefutable proof could only be had, as he saw it, by
"extracting" the lightning with something actually sent up into the storm-
cloud; and to accomplish this Franklin made his silk kite, with which he
finally demonstrated to his own and the world's satisfaction that his theory
was correct.
Taking his kite out into an open common on the approach of a thunder-
storm, he flew it well up into the threatening clouds, and then, touching, the
suspended key with his knuckle, received the electric spark; and a little later
he charged a Leyden jar from the electricity drawn from the clouds with his
kite.
In a brief but direct letter, he sent an account of his kite and his
experiment to England:
"Make a small cross of two light strips of cedar," he wrote, "the arms so
long as to reach to the four corners of a large, thin, silk handkerchief when
extended; tie the corners of the handkerchief to the extremities of the cross
so you have the body of a kite; which being properly accommodated with a
tail, loop, and string, will rise in the air like those made of paper; but this
being of silk is fitter to bear the wind and wet of a thunder-gust without
tearing. To the top of the upright stick of the cross is to be fixed a very
sharp-pointed wire, rising a foot or more above the wood. To the end of the
twine, next the hand, is to be tied a silk ribbon; where the silk and twine
join a key may be fastened. This kite is to be raised when a thunder-gust
appears to be coming on, and the person who holds the string must stand
within a door or window or under some cover, so that the silk ribbon may
not be wet; and care must be taken that the twine does not touch the frame
of the door or window. As soon as any of the thunder-clouds come over the
kite, the pointed wire will draw the electric fire from them, and the kite,
with all the twine, will be electrified and the loose filaments will stand out
everywhere and be attracted by the approaching finger, and when the rain

has wet the kite and twine so that it can conduct the electric fire freely, you
will find it stream out plentifully from the key on the approach of your
knuckle, and with this key the phial may be charged; and from electric fire
thus obtained spirits may be kindled and all other electric experiments
performed which are usually done by the help of a rubbed glass globe or
tube, and thereby the sameness of the electric matter with that of lightning
completely demonstrated."(5)
In experimenting with lightning and Franklin's pointed rods in Europe,
several scientists received severe shocks, in one case with a fatal result.
Professor Richman, of St. Petersburg, while experimenting during a
thunder-storm, with an iron rod which he had erected on his house, received
a shock that killed him instantly.
About 1733, as we have seen, Dufay had demonstrated that there were
two apparently different kinds of electricity; one called VITREOUS
because produced by rubbing glass, and the other RESINOUS because
produced by rubbed resinous bodies. Dufay supposed that these two
apparently different electricities could only be produced by their respective
substances; but twenty years later, John Canton (1715-1772), an
Englishman, demonstrated that under certain conditions both might be
produced by rubbing the same substance. Canton's experiment, made upon
a glass tube with a roughened surface, proved that if the surface of the tube
were rubbed with oiled silk, vitreous or positive electricity was produced,
but if rubbed with flannel, resinous electricity was produced. He discovered
still further that both kinds could be excited on the same tube
simultaneously with a single rubber. To demonstrate this he used a tube,
one-half of which had a roughened the other a glazed surface. With a single
stroke of the rubber he was able to excite both kinds of electricity on this
tube. He found also that certain substances, such as glass and amber, were
electrified positively when taken out of mercury, and this led to his
important discovery that an amalgam of mercury and tin, when used on the
surface of the rubber, was very effective in exciting glass.

XV. NATURAL HISTORY TO THE TIME OF
LINNAEUS
Modern systematic botany and zoology are usually held to have their
beginnings with Linnaeus. But there were certain precursors of the famous
Swedish naturalist, some of them antedating him by more than a century,
whose work must not be altogether ignored—such men as Konrad Gesner
(1516-1565), Andreas Caesalpinus (1579-1603), Francisco Redi (1618-
1676), Giovanni Alfonso Borelli (1608-1679), John Ray (1628-1705),
Robert Hooke (1635-1703), John Swammerdam (1637-1680), Marcello
Malpighi (1628-1694), Nehemiah Grew (1628-1711), Joseph Tournefort
(1656-1708), Rudolf Jacob Camerarius (1665-1721), and Stephen Hales
(1677-1761). The last named of these was, to be sure, a contemporary of
Linnaeus himself, but Gesner and Caesalpinus belong, it will be observed,
to so remote an epoch as that of Copernicus.
Reference has been made in an earlier chapter to the microscopic
investigations of Marcello Malpighi, who, as there related, was the first
observer who actually saw blood corpuscles pass through the capillaries.
Another feat of this earliest of great microscopists was to dissect muscular
tissue, and thus become the father of microscopic anatomy. But Malpighi
did not confine his observations to animal tissues. He dissected plants as
well, and he is almost as fully entitled to be called the father of vegetable
anatomy, though here his honors are shared by the Englishman Grew. In
1681, while Malpighi's work, Anatomia plantarum, was on its way to the
Royal Society for publication, Grew's Anatomy of Vegetables was in the
hands of the publishers, making its appearance a few months earlier than
the work of the great Italian. Grew's book was epoch-marking in pointing
out the sex-differences in plants.
Robert Hooke developed the microscope, and took the first steps towards
studying vegetable anatomy, publishing in 1667, among other results, the
discovery of the cellular structure of cork. Hooke applied the name "cell"
for the first time in this connection. These discoveries of Hooke, Malpighi,
and Grew, and the discovery of the circulation of the blood by William

Harvey shortly before, had called attention to the similarity of animal and
vegetable structures. Hales made a series of investigations upon animals to
determine the force of the blood pressure; and similarly he made numerous
statical experiments to determine the pressure of the flow of sap in
vegetables. His Vegetable Statics, published in 1727, was the first important
work on the subject of vegetable physiology, and for this reason Hales has
been called the father of this branch of science.
In botany, as well as in zoology, the classifications of Linnaeus of course
supplanted all preceding classifications, for the obvious reason that they
were much more satisfactory; but his work was a culmination of many
similar and more or less satisfactory attempts of his predecessors. About the
year 1670 Dr. Robert Morison (1620-1683), of Aberdeen, published a
classification of plants, his system taking into account the woody or
herbaceous structure, as well as the flowers and fruit. This classification
was supplanted twelve years later by the classification of Ray, who
arranged all known vegetables into thirty-three classes, the basis of this
classification being the fruit. A few years later Rivinus, a professor of
botany in the University of Leipzig, made still another classification,
determining the distinguishing character chiefly from the flower, and
Camerarius and Tournefort also made elaborate classifications. On the
Continent Tournefort's classification was the most popular until the time of
Linnaeus, his systematic arrangement including about eight thousand
species of plants, arranged chiefly according to the form of the corolla.
Most of these early workers gave attention to both vegetable and animal
kingdoms. They were called naturalists, and the field of their investigations
was spoken of as "natural history." The specialization of knowledge had not
reached that later stage in which botanist, zoologist, and physiologist felt
their labors to be sharply divided. Such a division was becoming more and
more necessary as the field of knowledge extended; but it did not become
imperative until long after the time of Linnaeus. That naturalist himself, as
we shall see, was equally distinguished as botanist and as zoologist. His
great task of organizing knowledge was applied to the entire range of living
things.
Carolus Linnaeus was born in the town of Rashult, in Sweden, on May
13, 1707. As a child he showed great aptitude in learning botanical names,
and remembering facts about various plants as told him by his father. His

eagerness for knowledge did not extend to the ordinary primary studies,
however, and, aside from the single exception of the study of physiology, he
proved himself an indifferent pupil. His backwardness was a sore trial to his
father, who was desirous that his son should enter the ministry; but as the
young Linnaeus showed no liking for that calling, and as he had acquitted
himself well in his study of physiology, his father at last decided to allow
him to take up the study of medicine. Here at last was a field more to the
liking of the boy, who soon vied with the best of his fellow-students for first
honors. Meanwhile he kept steadily at work in his study of natural history,
acquiring considerable knowledge of ornithology, entomology, and botany,
and adding continually to his collection of botanical specimens. In 1729 his
botanical knowledge was brought to the attention of Olaf Rudbeck,
professor of botany in the University of Upsala, by a short paper on the
sexes of plants which Linnaeus had prepared. Rudbeck was so impressed by
some of the ideas expressed in this paper that he appointed the author as his
assistant the following year.
This was the beginning of Linnaes's career as a botanist. The academic
gardens were thus thrown open to him, and he found time at his disposal for
pursuing his studies between lecture hours and in the evenings. It was at
this time that he began the preparation of his work the Systema naturae, the
first of his great works, containing a comprehensive sketch of the whole
field of natural history. When this work was published, the clearness of the
views expressed and the systematic arrangement of the various
classifications excited great astonishment and admiration, and placed
Linaeus at once in the foremost rank of naturalists. This work was followed
shortly by other publications, mostly on botanical subjects, in which, among
other things, he worked out in detail his famous "system."
This system is founded on the sexes of plants, and is usually referred to
as an "artificial method" of classification because it takes into account only
a few marked characters of plants, without uniting them by more general
natural affinities. At the present time it is considered only as a stepping-
stone to the "natural" system; but at the time of its promulgation it was
epoch-marking in its directness and simplicity, and therefore superiority,
over any existing systems.
One of the great reforms effected by Linnaeus was in the matter of
scientific terminology. Technical terms are absolutely necessary to scientific

progress, and particularly so in botany, where obscurity, ambiguity, or
prolixity in descriptions are fatally misleading. Linnaeus's work contains
something like a thousand terms, whose meanings and uses are carefully
explained. Such an array seems at first glance arbitrary and unnecessary, but
the fact that it has remained in use for something like two centuries is
indisputable evidence of its practicality. The descriptive language of botany,
as employed by Linnaeus, still stands as a model for all other subjects.
Closely allied to botanical terminology is the subject of botanical
nomenclature. The old method of using a number of Latin words to describe
each different plant is obviously too cumbersome, and several attempts had
been made prior to the time of Linnaeus to substitute simpler methods.
Linnaeus himself made several unsatisfactory attempts before he finally hit
upon his system of "trivial names," which was developed in his Species
plantarum, and which, with some, minor alterations, remains in use to this
day. The essence of the system is the introduction of binomial nomenclature
—that is to say, the use of two names and no more to designate any single
species of animal or plant. The principle is quite the same as that according
to which in modern society a man has two names, let us say, John Doe, the
one designating his family, the other being individual. Similarly each
species of animal or plant, according to the Linnaeean system, received a
specific or "trivial" name; while various species, associated according to
their seeming natural affinities into groups called genera, were given the
same generic name. Thus the generic name given all members of the cat
tribe being Felis, the name Felis leo designates the lion; Felis pardus, the
leopard; Felis domestica, the house cat, and so on. This seems perfectly
simple and natural now, but to understand how great a reform the binomial
nomenclature introduced we have but to consult the work of Linnaeus's
predecessors. A single illustration will suffice. There is, for example, a kind
of grass, in referring to which the naturalist anterior to Linnaeus, if he
would be absolutely unambiguous, was obliged to use the following
descriptive formula: Gramen Xerampelino, Miliacea, praetenuis ramosaque
sparsa panicula, sive Xerampelino congener, arvense, aestivum; gramen
minutissimo semine. Linnaeus gave to this plant the name Poa bulbosa—a
name that sufficed, according to the new system, to distinguish this from
every other species of vegetable. It does not require any special knowledge
to appreciate the advantage of such a simplification.

While visiting Paris in 1738 Linnaeus met and botanized with the two
botanists whose "natural method" of classification was later to supplant his
own "artificial system." These were Bernard and Antoine Laurent de
Jussieu. The efforts of these two scientists were directed towards obtaining
a system which should aim at clearness, simplicity, and precision, and at the
same time be governed by the natural affinities of plants. The natural
system, as finally propounded by them, is based on the number of
cotyledons, the structure of the seed, and the insertion of the stamens.
Succeeding writers on botany have made various modifications of this
system, but nevertheless it stands as the foundation-stone of modern
botanical classification.

APPENDIX
REFERENCE LIST

CHAPTER I
SCIENCE IN THE DARK AGE

(1) (p. 4). James Harvey Robinson, An Introduction to the History of
Western Europe, New York, 1898, p. 330.
(2) (p. 6). Henry Smith Williams, A Prefatory Characterization of The
History of Italy, in vol. IX. of The Historians' History of the World, 25
vols., London and New York, 1904.

CHAPTER III
MEDIAEVAL SCIENCE IN THE WEST

(1) (p. 47). Etigene Muntz, Leonardo do Vinci, Artist, Thinker, and Man
of Science, 2 vols., New York, 1892. Vol. II., p. 73.

CHAPTER IV
THE NEW COSMOLOGY—COPERNICUS TO KEPLER
AND GALILEO

(1) (p. 62). Copernicus, uber die Kreisbewegungen der Welfkorper, trans.
from Dannemann's Geschichle du Naturwissenschaften, 2 vols., Leipzig,
1896.
(2) (p. 90). Galileo, Dialogo dei due Massimi Systemi del Mondo, trans.
from Dannemann, op. cit.

CHAPTER V
GALILEO AND THE NEW PHYSICS (1) (p. 101). Rothmann, History
of Astronomy (in the Library of Useful Knowledge), London, 1834.
(2) (p. 102). William Whewell, History of the Inductive Sciences, 3 Vols,
London, 1847-Vol. II., p. 48.
(3) (p. 111). The Lives of Eminent Persons, by Biot, Jardine, Bethune,
etc., London, 1833.
(4) (p. 113). William Gilbert, De Magnete, translated by P. Fleury
Motteley, London, 1893. In the biographical memoir, p. xvi.
(5) (p. 114). Gilbert, op. cit., p. x1vii.
(6) (p. 114). Gilbert, op. cit., p. 24.

CHAPTER VI
TWO PSEUDO-SCIENCES—ALCHEMY AND
ASTROLOGY

(1) (p. 125). Exodus xxxii, 20.
(2) (p. 126). Charles Mackay, Popular Delusions, 3 vols., London, 1850.
Vol. II., p. 280.
(3) (p. 140). Mackay, op. cit., Vol. 11., p. 289.
(4) (P. 145). John B. Schmalz, Astrology Vindicated, New York, 1898.
(5) (p. 146). William Lilly, The Starry Messenger, London, 1645, p. 63.
(6) (p. 149). Lilly, op. cit., p. 70.
(7) (p. 152). George Wharton, An Astrological judgement upon His
Majesty's Present March begun from Oxford, May 7, 1645, pp. 7-10.
(8) (p. 154). C. W. Roback, The Mysteries of Astrology, Boston, 1854, p.
29.

CHAPTER VII
FROM PARACELSUS TO HARVEY

(1) (p. 159). A. E. Waite, The Hermetic and Alchemical Writings of
Paracelsus, 2 vols., London, 1894. Vol. I., p. 21.
(2) (p. 167). E. T. Withington, Medical History from the Earliest Times,
London, 1894, p. 278.
(3) (p. 173). John Dalton, Doctrines of the Circulation, Philadelphia,
1884, p. 179.
(4) (p. 174). William Harvey, De Motu Cordis et Sanguinis, London,
1803, chap. X.
(5) (p. 178). The Works of William Harvey, translated by Robert Willis,
London, 1847, p. 56.

CHAPTER VIII
MEDICINE IN THE SIXTEENTH AND SEVENTEENTH
CENTURIES

(1) (p. 189). Hermann Baas, History of Medicine, translated by H. E.
Henderson, New York, 1894, p. 504.
(2) (p. 189). E. T. Withington, Medical History from the Earliest Times,
London, 1894, p. 320.

CHAPTER IX
PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS
OF LEARNING

(1) (p. 193). George L. Craik, Bacon and His Writings and Philosophy, 2
vols., London, 1846. Vol. II., p. 121.
(2) (p. 193). From Huxley's address On Descartes's Discourse Touching
the Method of Using One's Reason Rightly and of Seeking Scientific Truth.
(3) (p. 195). Rene Descartes, Traite de l'Homme (Cousins's edition. in ii
vols.), Paris, 1824. Vol, VI., p. 347.

CHAPTER X
THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE

(1) (p. 205). See The Phlogiston Theory, Vol, IV.
(2) (p. 205). Robert Boyle, Philosophical Works, 3 vols., London, 1738.
Vol. III., p. 41.
(3) (p. 206). Ibid., Vol. III., p. 47.
(4) (p. 206). Ibid., Vol. II., p. 92.
(5) (p. 207). Ibid., Vol. II., p. 2.
(6) (p. 209). Ibid., Vol. I., p. 8.
(7) (p. 209). Ibid., vol. III., p. 508.
(8) (p. 210). Ibid., Vol. III., p. 361.
(9) (p. 213). Otto von Guericke, in the Philosophical Transactions of the
Royal Society of London, No. 88, for 1672, p. 5103.
(10) (p. 222). Von Guericke, Phil. Trans. for 1669, Vol I., pp. 173, 174.

CHAPTER XI
NEWTON AND THE COMPOSITION OF LIGHT

(1) (p. 233). Phil. Trans. of Royal Soc. of London, No. 80, 1672, pp.
3076-3079. (2) (p 234). Ibid., pp. 3084, 3085.
(3) (p. 235). Voltaire, Letters Concerning the English Nation, London,
1811.

CHAPTER XII
NEWTON AND THE LAW OF GRAVITATION

(1) (p. 242). Sir Isaac Newton, Principia, translated by Andrew Motte,
New York, 1848, pp. 391, 392.
(2) (p. 250). Newton op. cit., pp. 506, 507.

CHAPTER XIV
PROGRESS IN ELECTRICITY FROM GILBERT AND VON
GUERICKE TO FRANKLIN

(1) (p. 274). A letter from M. Dufay, F.R.S. and of the Royal Academy of
Sciences at Paris, etc., in the Phil. Trans. of the Royal Soc., vol. XXXVIII.,
pp. 258-265.
(2) (p. 282). Dean von Kleist, in the Danzick Memoirs, Vol. I., p. 407.
From Joseph Priestley's History of Electricity, London, 1775, pp. 83, 84.
(3) (p. 288). Benjamin Franklin, New Experiments and Observations on
Electricity, London, 1760, pp. 107, 108.
(4) (p. 291). Franklin, op. cit., pp. 62, 63.
(5) (p. 295). Franklin, op. cit., pp. 107, 108.
(For notes and bibliography to vol. II. see vol. V.)

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

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