The Poetry of Science_ or_ Studies of the Physical Phenomena of Nature Robert Hunt 988 downloads.pdf

The Project Gutenberg eBook of The Poetry of Science; or,
Studies of the Physical Phenomena of Nature
This eBook is for the use of anyone anywhere in the United States and
most other parts of the world at no cost and with almost no restrictions
whatsoever. You may copy it, give it away or re-use it under the terms
of the Project Gutenberg License included with this eBook or online at
www.gutenberg.org. If you are not located in the United States, you
will have to check the laws of the country where you are located
before using this eBook.

Title: The Poetry of Science; or, Studies of the Physical Phenomena of
Nature

Author: Robert Hunt

Release date: April 30, 2016 [eBook #51897]
Most recently updated: October 23, 2024

Language: English

Other information and formats: www.gutenberg.org/ebooks/51897

Credits: Produced by Emmanuel Ackerman and the Online Distributed
Proofreading Team at http://www.pgdp.net (This file was
produced from images generously made available by The
Internet Archive/Canadian Libraries)

*** START OF THE PROJECT GUTENBERG EBOOK THE POETRY
OF SCIENCE; OR, STUDIES OF THE PHYSICAL PHENOMENA OF
NATURE ***

THE

POETRY OF SCIENCE;
OR,

STUDIES
OF THE

PHYSICAL PHENOMENA OF NATURE.

BY

ROBERT HUNT,
AUTHOR OF
“RESEARCHES ON LIGHT;” “ELEMENTARY PHYSICS;” “PANTHEA, OR THE SPIRIT OF
NATURE,” ETC.
PROFESSOR OF PHYSICS, METROPOLITAN SCHOOL OF SCIENCE, ETC., ETC.

THIRD EDITION, REVISED AND ENLARGED.

LONDON:
HENRY G. BOHN, YORK STREET, COVENT GARDEN.
MDCCCLIV.

From Shakespeare to Plato—from the philosophic poet to the poetic
philosopher—the transition is easy, and the road is crowded with
illustrations of our present subject.

Hast thou ever raised thy mind to the consideration of existence, in and by
itself, as the mere act of existing?
Hast thou ever said to thyself, thoughtfully, It is!—heedless, in that
moment, whether it were a man before thee, or a flower, or a grain of
sand,—without reference, in short, to this or that particular mode or
form of existence? If thou hast, indeed, attained to this, thou wilt have
felt the presence of a mystery, which must have fixed thy spirit in awe
and wonder.
Coleridge.

London:
Wilson and Ogilvy,
57, Skinner Street.

PREFACE.
Since 1848, when the “Poetry of Science” was first submitted to the public,
two editions have been exhausted. This, were proofs required, would of
itself show that there is a large circle of readers to whom the deductions of
science have an unfailing interest. Beyond this, it conveys an assurance that
every truth, however abstract it may appear, has a large popular value if
studied in its relations to those generalities which embrace great natural
phenomena. With this persuasion the third edition of the “Poetry of
Science” has been extended so as to include all the important discoveries
which have been made in Natural Philosophy to the end of the year 1853. It
is now presented to the world in a new and cheaper form, in the hope, that,
with the extension of its circulation, there may be awakened, in still larger
circles, a deep and healthful interest in the sciences of which the volume
treats.
R. H.
Edinburgh, March 7, 1854.

CONTENTS.
Page

PREFACE. iii

CONTENTS. v

INTRODUCTION. ix

CHAPTER I.

GENERAL CONDITIONS
OF MATTER.
Its varied Characters, and
constant change of
external Form—The
Grain of Dust, its
Properties and Powers
—Combinations in
inorganic Masses and
in organized Creations
—Our knowledge of
Matter—Theory of
Ultimate Atoms—The
Physical Forces acting
on the Composition of
Masses—The
certainty of the
exercise of subtile
principles, which are
beyond the reach of
experimental Science 1

CHAPTER II.

MOTION.
Are the Physical Forces
modes of Motion?—
Motion defined—
Philosophical Views
of Motion, and the
Principles to which it
has been referred—
Motions of the Earth
and of the Solar
System—Visible
Proofs of the Earth’s
Motion on its Axis—
Influence of the proper
Motions of the Earth
on the Conditions of
Matter—Theory of the
Conversion of Motion
into Heat, &c.—The
Physical Forces
regarded as principles
independent of
Motion, although the
Cause and often
apparently the Effects
of it 7

CHAPTER III.

GRAVITATION.
The Forms of Matter—
Shape of the Earth—
Probability of the
Mass forming this
Planet having existed
in a Nebulous State—
Zodiacal Lights—
Comets—
Volatilization of Solid
Matter by Artificial
means—The principle
of Gravitation—Its
Influence through
Space and within the
smallest Limits—
Gravitating powers of
the Planets—Density
of the Earth—
Certainty of Newton’s
Law of the Inverse
Square—Discovery of
Neptune—State of a
Body relieved from
Gravitation—
Experiment explaining
Saturn’s Ring, &c.—
General inference 21

CHAPTER IV.

MOLECULAR FORCES.
Conditions of Matter—
Variety of organized
Forms—Inorganic
Forms—All matter
reducible to the most
simple conditions—
Transmutation, a
natural operation—
Chemical Elementary
Principles—
Divisibility of Matter
—Atom—Molecules
—Particles—
Molecular Force
includes several
Agencies—Instanced
in the Action of Heat
on Bodies—All
Bodies porous—
Solution—Mixture—
Combination—
Centres of Force—
Different States of
Matter (Allotropic
Conditions)—
Theories of Franklin,
Æpinus, and Coulomb
—Electrical and
Magnetic Agencies—
Ancient Notions—
Cohesive Attraction,
&c. 35

CHAPTER V.

CRYSTALLOGENIC
FORCES.
Crystallisation and
Molecular Force
distinguished—
Experimental Proof—
Polarity of Particles
forming a Crystal—
Difference between
Organic and Inorganic
Forms—
Decomposition of
Crystals in Nature—
Substitution of
Particles in Crystals—
Pseudomorphism—
Crystalline Form not
dependent on
Chemical Nature—
Isomorphism—
Dimorphism—
Theories of
Crystallogenic
Attraction—Influence
of Electricity and
Magnetism—
Phenomena during
Crystallisation—Can a
change of Form take
place in Primitive
Atoms?—Illustrative
Example of
Crystallisation 50

CHAPTER VI.

HEAT—SOLAR AND
TERRESTRIAL.
Solar and Terrestrial Heat 62
—Position of the
Earth in the Solar
System—Heat and
Light associated in the
Sunbeam—
Transparency of
Bodies to Heat—
Heating Powers of the
Coloured Rays of the
Spectrum—
Undulatory Theory—
Conducting Property
of the Earth’s Crust—
Convection—
Radiation—Action of
the Atmosphere on
Heat Rays—Peculiar
Heat Rays—
Absorption and
Radiation of Heat by
dissimilar Bodies—
Changes in the
Constitution of Solar
Beam—Differences
between Transmitted
and Reflected Solar
Heat—Phenomena of
Dew—Action of Solar
Heat of the Ocean—
Circulation of Heat by
the Atmosphere and
the Ocean—Heat of
the Earth—Mean
Temperature—Central

Heat—Constant
Radiation of Heat
Rays from all Bodies
—Thermography—
Action of Heat on
Molecular
Arrangements—
Sources of Terrestrial
Heat—Latent Heat of
Bodies—Animal Heat
—Eremacausis—
Spheroidal State Cold
—Condensation—
Freezing—Theories of
Heat—Natural
Phenomena—and
Philosophical
Conclusion

CHAPTER VII.

LIGHT.
Theories of the Nature of
Light—Hypotheses of
Newton and Huygens
—Sources of Light—
The Sun—Velocity of
Light—Transparency
—Dark Lines of the
Spectrum—
Absorption of Light—
Colour—Prismatic
Analysis—Rays of the
Spectrum—Rainbow
—Diffraction—
Interference—
Goethe’s Theory—
Polarisation—
Magnetisation of
Light—Vision—The
Eye—Analogy—
Sound and Light—
Influence of Light on
Animals and
Vegetables—
Phosphorescence
arising from several
Causes—Artificial
Light—Its Colour
dependent on Matter 118

CHAPTER VIII.

ACTINISM—CHEMICAL
RADIATIONS.
The Sun-ray and its Powers
—Darkening of Horn
Silver—Niepce’s
Discovery—Prismatic
Spectrum—
Refrangibility of
Light, Heat, and
Actinism—Daguerre’s
Discovery—
Photography—
Chemical Effects
produced by Solar
Radiations—
Absorption of
Actinism—
Phenomena of the
Daguerreotype—
Chemical Change
produced upon all
Bodies—Power of
Matter to restore its
Condition—Light
protects from
Chemical Change—
Photographs taken in
Darkness—Chemical
Effects of Light on
organized Forms—
Chemical Effects of
Solar Heat—Influence
of Actinism on
Electricity—
Radiations in
Darkness—Moser’s
Discoveries, &c. 166

CHAPTER IX.

ELECTRICITY.
Discovery of Electrical 193
Force—Diffused
through all Matter—
What is Electricity?—
Theories—Frictional
Electricity—
Conducting Power of
Bodies—Hypothesis
of two Fluids—
Electrical Images—
Galvanic Electricity—
Effects on Animals—
Chemistry of Galvanic
Battery—Electricity of
a Drop of Water—
Electro-chemical
Action—Electrical
Currents—Thermo-
Electricity—Animal
Electricity—
Gymnotus—Torpedo
—Atmospheric
Electricity—Lightning
Conductors—Earth’s
Magnetism due to
Electrical Currents—
Influence on Vitality
—Animal and
Vegetable
Development—
Terrestrial Currents—
Electricity of Mineral
Veins—Electrotype—
Influence of Heat,
Light, and Actinism

on Electrical
Phenomena

CHAPTER X.

MAGNETISM.
Magnetic Iron—
Knowledge of, by the
Ancients—Artificial
Magnets—Electro-
Magnets—Electro-
Magnetism—
Magneto-Electricity—
Theories of
Magnetism—The
Magnetic Power of
soft Iron and Steel—
Influence of Heat on
Magnetism—
Terrestrial Magnetism
—Declination of the
Compass-needle—
Variation of the
Earth’s Magnetism—
Magnetic Poles—
Hansteen’s
Speculations—
Monthly and Diurnal
Variation—Dip and
Intensity—Thermo-
Magnetism—Aurora
Borealis—Magnetic
Storms—Magnetic
conditions of Matter—
Diamagnetism, &c. 235

CHAPTER XI.

CHEMICAL FORCES.
Nature’s Chemistry—
Changes produced by
Chemical
Combination—
Atomic Constitution
of Bodies—Laws of
Combination—
Combining
Equivalents—Elective
Affinity—Chemical
Decomposition—
Compound Character
of Chemical
Phenomena—
Catalysis or action of
Presence—
Transformation of
Organic Bodies—
Organic Chemistry—
Constancy of
Combining
Proportions—The
Law of Volumes, the
Law of Substitutions,
Isomeric States, &c. 270

CHAPTER XII.

CHEMICAL
PHENOMENA.
Water—Its Constituents—
Oxygen—Hydrogen—
Peroxide of Hydrogen
—Physical Property of
Water—Ice—Sea
Water—Chlorine—
Muriatic Acid—Iodine
—Bromine—
Compounds of
Hydrogen with
Carbon—Combustion
—Flame—Safety
Lamp—Respiration—
Animal Heat—The
Atmosphere—
Carbonic Acid—
Influence of Plants on
the Air—Chemical
Phenomena of
Vegetation—
Compounds of
Nitrogen—Mineral
Kingdom, &c. &c. 295

CHAPTER XIII.

TIME.—GEOLOGICAL
PHENOMENA.
Time, an element in
Nature’s Operations—
Geological Science—
Its Facts and
Inferences—Nebular
Hypothesis applied—
Primary Formations—
Plutonic and
Metamorphic Rocks—
Transition Series—
Palæozoic Rocks—
Commencement of
Organic Arrangements
—Existence of
Phosphoric Acid in
Plutonic Rocks—
Fossil Remains—Coal
Formation—
Sandstones—Tertiary
Formations—Eocene,
Miocene, and Pliocene
Formations—
Progressive changes
now apparent—
General Conclusions
—Physics applied in
explanation 332

CHAPTER XIV.

PHENOMENA OF
VEGETABLE LIFE.
Psychology of Flowers—
Progress of Matter
towards Organization
—Vital Force—
Spontaneous
Generation—The
Vegetable Cell—
Simplest Development
of Organization—The
Crystal and the Cell—
Primitive Germ—
Progress of Vegetation
—Influence of Light
—Morphology—
Germination—
Production of Woody
Fibre—Leaves—
Chlorophylle—
Decomposition of
Carbonic Acid—
Influence of Light,
Heat, and Actinism on
the Phenomena of
Vegetable Life—
Flowers and Fruits—
Etiolation—Changes
in the Sun’s Rays with
the Seasons—
Distribution of Plants
—Electrical and
Combined Physical
Powers 357

CHAPTER XV.

PHENOMENA OF
ANIMAL LIFE.
Distinction between the
Kingdoms of Nature
—Progress of Animal
Life—Sponges—
Polypes—Infusoria—
Animalcula—
Phosphorescent
Animals—Annelidans
—Myriapoda—
Animal
Metamorphoses—
Fishes—Birds—
Mammalia—Nervous
System—Animal
Electricity—Chemical
Influences—Influence
of Light on Animal
Life—Animal Heat—
Mechanical Action—
Nervous Excitement—
Man and the Animal
Races, &c. 383

CHAPTER XVI.

GENERAL
CONCLUSIONS.
The Changes produced on
Physical Phenomena
by the Movement of
the Solar System
considered—Exertion
of the Physical Forces
through the Celestial
Spaces—The Balance
of Powers—Varieties
of Matter—Extension
of Matter—Theory of
Nonentity—A
Material Creation an
indisputable fact—
Advantages of the
Study of Science—
Conclusion 403

INDEX. 413

BOHN’S BOOKS.

TRANSCRIBER’S
NOTE.

INTRODUCTION.
The True is the Beautiful. Whenever this becomes evident to our senses, its
influences are of a soul-elevating character. The beautiful, whether it is
perceived in the external forms of matter, associated in the harmonies of
light and colour, appreciated in the modulations of sweet sounds, or
mingled with those influences which are, as the inner life of creation, ever
appealing to the soul through the vesture which covers all things, is the
natural theme of the poet, and the chosen study of the philosopher.
But, it will be asked, where is the relation between the stern labours of
science and the ethereal system which constitutes poetry? The fumes of the
laboratory, its alkalies and acids, the mechanical appliances of the
observatory, its specula and its lenses, do not appear fitted for a place in the
painted bowers of the Muses. But, from the labours of the chemist in his
cell,—from the multitudinous observations of the astronomer on his tower,
—spring truths which the philosopher employs to interpret nature’s
mysteries, and which give to the soul of the poet those realities to which he
aspires in his high imaginings.
Science solicits from the material world, by the persuasion of inductive
search, a development of its elementary principles, and of the laws which
these obey. Philosophy strives to apply the discovered facts to the great
phenomena of being,—to deduce large generalities from the fragmentary
discoveries of severe induction,—and thus to ascend from matter and its
properties up to those impulses which stir the whole, floating, as it were, on
the confines of sense, and indicating, though dimly, those superior powers
which, more nearly related to infinity, mysteriously manifest themselves in
the phenomena of mind. Poetry seizes the facts of the one and the theories
of the other; unites them by a pleasing thought, which appeals for truth to
the most unthinking soul, and leads the reflective intellect to higher and
higher exercises; it connects common phenomena with exalted ideas; and,
applying its holiest powers, it invests the human mind with the sovereign
strength of the True.

Truth is the soul of the poet’s thought;—truth is the reward of the
philosopher’s toil; and their works, bearing this stamp, live among men
through all time. Science at present rejoices in her ministry to the
requirements of advancing civilization, and is content to receive the reward
given to applications which increase the comforts of life, or add to its
luxuries. Every improvement in the arts or manufactures, beyond
encreasing utilities for society, has a tendency to elevate the race. Science is
ever useful in the working days of our week, but it is not to be neglected on
our Sabbath,—when, resting from our labours, it becomes agreeable to
contemplate the few truths permitted to our knowledge, and thus enter into
communion as closely as is allowed to finite beings, with those influences
which involve and interpenetrate the earth, giving to all things Life, Beauty,
and Divinity.
The human mind naturally delights in the discovery of truth; and even when
perverted by the constant operations of prevailing errors, a glimpse of the
Real comes upon it like the smile of daylight to the sorrowing captive of
some dark prison. The Psychean labours to try man’s soul, and exalt it, are
the search for truth beneath the mysteries which surround creation,—to
gather amaranths, shining with the hues of heaven, from plains upon which
hang, dark and heavy, the mists of earth. The poet may pay the debt of
nature,—the philosopher may return to the bosom of our common mother,
—even their names fade in the passage of time, like planets blotted out of
heaven but the truths they have revealed to man burn on for ever with
unextinguishable brightness. Truth cannot die; it passes from mind to mind,
imparting light in its progress, and constantly renewing its own brightness
during its diffusion. The True is the Beautiful; and the truths revealed to the
mind render us capable of perceiving new beauties on the earth. The
gladness of truth is like the ringing voice of a joyous child, and the most
remote recesses echo with the cheerful sound. To be for ever true is the
Science of Poetry,—the revelation of truth is the Poetry of Science.
Man, a creation endued with mighty faculties, but a mystery to himself,
stands in the midst of a wonderful world, and an infinite variety of
phenomena arise around him in strange form and magical disposition, like
the phantasma of a restless night.
The solid rock obeys a power which brings its congeries of atoms into a
thousand shapes, each one geometrically perfect. Its vegetable covering, in

obedience to some external excitation, developes itself in a curious diversity
of forms, from the exquisitely graceful to the singularly grotesque, and
exhibits properties still more varied and opposed. The animal organism
quickened by higher impulses,—powers working within, and modifying the
influence of the external forces,—presents, from the Monad to the
Mammoth, and through every phase of being up to Man, a yet more
wonderful series of combinations, and features still more strangely
contrasted.
Lifting our searching gaze into the measureless space beyond our earth, we
find planet bound to planet, and system chained to system, all impelled by a
universal force to roll in regularity and order around a common centre. The
pendulations of the remotest star are communicated through the unseen
bond; and our rocking world obeys the mysterious impulse throughout all
those forces which regulate the inorganic combinations of this earth, and
unto which its organic creation is irresistibly compelled to bow.
The glorious sun by day, and the moon and stars in the silence and the
mystery of night, are felt to influence all material nature, holding the great
Earth bound in a many-stranded cord which cannot be broken. The tidal
flow of the vast ocean, with its variety of animal and vegetable life, the
atmosphere, bright with light, obscured by the storm-cloud, spanned by the
rainbow, or rent with the explosions of electric fire,—attest to the might of
these elementary bonds.
These are but a few of the great phenomena which play their part around
this globe of ours, exciting men to wonder, or shaking them with terror.
The mind of man, in its progress towards its higher destiny, is tasked with
the physical earth as a problem, which, within the limits of a life, it must
struggle to solve. The intellectual spirit is capable of embracing all finite
things. Man is gifted with powers for studying the entire circle of visible
creation; and he is equal, under proper training, to the task of examining
much of the secret machinery which stirs the whole.
In dim outshadowing, earth’s first poets, from the loveliness of external
nature, evoked beautiful spiritualizations. To them the shady forests teemed
with aërial beings,—the gushing springs rejoiced in fantastic sprites,—the
leaping cataracts gleamed with translucent shades,—the cavernous hills
were the abodes of genii,—and the earth-girdling ocean was guarded by

mysterious forms. Such were the creations of the far-searching mind in its
early consciousness of the existence of unseen powers. The philosopher
picked out his way through the dark and labyrinthine path, between effects
and causes, and slowly approaching towards the light, he gathered
semblances of the great Reality, like a mirage, beautiful and truthful,
although still but a cloud-reflection of the vast Unseen.
It is thus that the human mind advances from the Ideal to the Real, and that
the poet becomes the philosopher, and the philosopher rises into the poet;
but at the same time as we progress from fable to fact, much of the soul-
sentiment which made the romantic holy, and gave a noble tone to every
aspiration, is too frequently merged in a cheerless philosophy which clings
to the earth, and reduces the mind to a mechanical condition, delighting in
the accumulation of facts, regardless of the great laws by which these are
regulated, and the harmony of all Telluric combinations secured. In science
we find the elements of the most exalted poetry; and in the mysterious
workings of the physical forces we discover connections with the illimitable
world of thought,—in which mighty minds delight to try their powers,—as
strangely complicated, and as marvellously ordered, as in the psychological
phenomena which have, almost exclusively, been the objects of their
studies.
In the aspect of visible nature, with its wonderful diversity of form and its
charm of colour, we find the Beautiful; and in the operations of these
principles, which are ever active in producing and maintaining the existing
conditions of matter, we discover the Sublime.
The form and colour of a flower may excite our admiration; but when we
come to examine all the phenomena which combine to produce that piece of
symmetry and that lovely hue,—to learn the physiological arrangement of
its structural parts,—the chemical actions by which its woody fibre and its
juices are produced,—and to investigate those laws by which is regulated
the power to throw back the white sunbeam from its surface in coloured
rays,—our admiration passes to the higher feeling of deep astonishment at
the perfection of the processes, and of reverence for their great Designer.
There are, indeed, “tongues in trees;” but science alone can interpret their
mysterious whispers, and in this consists its poetry.

To rest content with the bare enunciation of a truth, is to perform but one
half of a task. As each atom of matter is involved in an atmosphere of
properties and powers, which unites it to every mass of the universe, so
each truth, however common it may be, is surrounded by impulses which,
being awakened, pass from soul to soul like musical undulations, and which
will be repeated through the echoes of space, and prolonged for all eternity.
The poetry which springs from the contemplation of the agencies which are
actively employed in producing the transformation of matter, and which is
founded upon the truths developed by the aids of science, should be in no
respect inferior to that which has been inspired by the beauty of the
individual forms of matter, and the pleasing character of their combinations.
The imaginative view of man and his world—the creations of the romantic
mind—have been, and ever will be, dwelt on with a soul-absorbing passion.
The mystery of our being, and the mystery of our ceasing to be, acting upon
intelligences which are for ever striving to comprehend the enigma of
themselves, leads by a natural process to a love for the Ideal. The discovery
of those truths which advance the human mind towards that point of
knowledge to which all its secret longings tend, should excite a higher
feeling than any mere creation of the fancy, how beautiful soever it may be.
The phenomena of Reality are more startling than the phantoms of the
Ideal. Truth is stranger than fiction. Surely many of the discoveries of
science which relate to the combinations of matter, and exhibit results
which we could not by any previous efforts of reasoning dare to reckon on,
results which show the admirable balance of the forces of nature, and the
might of their uncontrolled power, exhibit to our senses subjects for
contemplation truly poetic in their character.
We tremble when the thunder-cloud bursts in fury above our heads. The
poet seizes on the terrors of the storm to add to the interest of his verse.
Fancy paints a storm-king, and the genius of romance clothes his demons in
lightnings, and they are heralded by thunders. These wild imaginings have
been the delight of mankind; there is subject for wonder in them: but is
there anything less wonderful in the well-authenticated fact, the dew-drop
which glistens on the flower, that the tear which trembles on the eye-lid,
holds locked in its transparent cells an amount of electric fire equal to that
which is discharged during a storm from a thunder-cloud?

In these studies of the effects which are continually presenting themselves
to the observing eye, and of the phenomena of causes, as far as they are
revealed by Science in its search of the physical earth, it will be shown that
beneath the beautiful vesture of the external world there exists, like its
quickening soul, a pervading power, assuming the most varied aspects,
giving to the whole its life and loveliness, and linking every portion of this
material mass in a common bond with some great universal principle
beyond our knowledge. Whether by the improvement of the powers of the
human mind, man will ever be enabled to embrace within his knowledge
the laws which regulate these remote principles, we are not sufficiently
advanced in intelligence to determine. But if admitted even to a clear
perception of the theoretical Power which we regard as regulating the
known forces, we must still see an unknown agency beyond us, which can
only be referred to the Creator’s will.

THE

POETRY OF SCIENCE.

CHAPTER I.
GENERAL CONDITIONS OF MATTER.
Its varied Characters, and constant change of external Form—The
Grain of Dust, its Properties and Powers—Combinations in
inorganic Masses and in organized Creations—Our
knowledge of Matter—Theory of Ultimate Atoms—The
Physical Forces acting on the Composition of Masses—The
certainty of the exercise of subtile principles, which are
beyond the reach of experimental Science.

The Physical Earth presents to us, in every form of organic and inorganic
matter, an infinite variety of phenomena. If we select specimens of rocks,
either crystalline or stratified,—of metals in any of their various
combinations with oxygen, sulphur, and other bodies,—of gems glistening
with light and glowing with colour,—if we examine the varied forms and
hues of the vegetable world, or the more mysterious animal creations, we
must inevitably come to the conclusion, long since proclaimed, and admit
that dust they are, and to dust must they return. Whatever permanency may
be given to matter, it is certain that its form is ever in a state of change. The
surface of the “Eternal Hills” is worn away by the soft rains which fall to
fertilize, and from their wrecks, borne by the waters to the ocean, new
continents are forming. The mutations of the old earth may be read upon her
rocks and mountains, and these records of former changes tell us the
infallible truth, that as the present passes into the future, so will the form of
Earth undergo an important alteration. The same forces which lifted the
Andes and the Himalayas are still at work, and from the particles of matter
carried from the present lands by the rivers into the sea, where they subside
in stratified masses, there will, in the great future, be raised new worlds,
upon which the work of life will go forward, and over which will be spread
a vast Intelligence.
If we regard the conditions of the beautiful and varied organic covering of
the Earth, the certainty, the constancy, of change is ever before us.

Vegetable life passes into the animal form, and both perish to feed the
future plant. Man, moving to-day the monarch of a mighty people, in a few
years passes back to his primitive clod, and that combination of elementary
atoms, which is dignified with the circle of sovereignty and the robe of
purple, after a period may be sought for in the herbage of the fields, or in
the humble flowers of the valley.
We have, then, this certain truth,—all things visible around us are but
aggregations of atoms. From particles of dust, which under the microscope
could scarcely be distinguished one from the other, are all the varied forms
of nature created. This grain of dust, this particle of sand, has strange
properties and powers. Science has discovered some truths, but still more
are hidden within this irregular molecule of matter which we now survey,
than have yet been shadowed in the dreams of our philosophy. How
strangely it obeys the impulses of heat—mysterious are the influences of
light upon it—electricity wonderfully excites it—and still more curious is
the manner in which it obeys the magic of chemical force. These are
phenomena which we have seen; we know them, and we can reproduce
them at our pleasure. We have advanced a little way into the secrets of
nature, and from the spot we have gained, we look forward with a vision
somewhat brightened by our task; but we discover so much to be yet
unknown, that we learn another truth,—our vast ignorance of many things
relating to this grain of dust.
It gathers around it other particles; they cling together, and each acting upon
every other one, and all of them arranging themselves around the little
centre according to some law, a beautiful crystal results, the geometric
perfection of its form being a source of admiration.
It exerts some other powers, and atom cohering to atom, obeying the
influences of many external radiant forces, undergoes inexplicable changes,
and the same dust which we find forming the diamond, aggregates into the
lordly tree,—blends to produce the graceful, scented, and richly painted
flower,—and combines to yield the luxury of fruit.
It quickens with yet undiscovered energies; it moves with life: dust is stirred
by the mysterious excitement of vital force; and blood and bone, nerve and
muscle, are the results. Forces, which we cannot by the utmost refinements
of our philosophy detect, direct the whole, and from the same dust which

formed the rock and grew in the tree, is produced a living and a breathing
thing, capable of receiving a Divine illumination, of bearing in its new state
the gladness and the glory of a Soul.
These considerations lead us to reflect on the amount of our knowledge. We
are led to ask ourselves, what do we know? We know that the world with all
its variety is composed of certain material atoms, which, although presented
to us in a great variety of forms, do not in all probability differ very
essentially from each other.
We know that those atoms obey certain conditions which appear to be
dependent upon the influences of motion, gravitation, heat, light, electricity,
and chemical force. These powers are only known to us by their effects; we
only detect their action by their operations upon matter; and although we
regard the several phenomena which we have discovered, as the
manifestations of different principles, it is possible they may be but
modifications of some one universal power, of which these are but a few of
its modes of action.
In examining, therefore, the truths which science has revealed to us, it is
advantageous, for the purpose of fixing the mind to the subject, that we
assume certain conditions as true. These may be stated in a few sentences,
and then, without wasting a thought upon those metaphysical subtleties
which have from time to time perplexed science, and served to impede the
progress of truth, we shall proceed to examine our knowledge of the
phenomena which constantly occur around us.
Every form, whether inorganic or organic, which we can discover within
the limits of human search, is composed of atoms, which are capable of
assuming, under the influence of certain physical forces, conditions
essential to the physical state of that body of which they constitute a part.[1]
The known forces, active in producing these conditions, are modes of
motion; gravitation and aggregation, heat, light; and associated with these,
actinism or chemical radiation; electricity, under all its conditions, whether
static or dynamic; and chemical affinity, regarded as the result of a separate
elementary principle.
These forces must be considered as powers capable of acting in perfect
independence of each other. They are possibly modifications of one
principle; but this view being an hypothesis, which, as yet, is only

supported by loose analogies, cannot, without danger, be received in any
explanation which attempts to deal only with the truths of science.
We cannot examine the varied phenomena of nature, without feeling that
there must be other and most active principles of a higher order than any
detected by science, to which belong the important operations of vitality,
whether manifested in the plant or the animal. In treating of these, although
speculation cannot be entirely avoided, it will be employed only so far as it
gives any assistance in linking phenomena together.
We have to deal with the active agencies which give form and feature to
nature—which regulate the harmony and beauty and vigour of life—and
upon which depend those grand changes in the conditions of matter, which
must convince us that death is but the commencement of a new state of
being.

FOOTNOTES:
[1] Sir Isaac Newton supposed matter to consist of hard, impenetrable, perfectly
inelastic atoms.
Boscovich regarded the constitution of matter differently. The ultimate atom was
with him a point surrounded by powers of infinite elasticity. (See Dr. Robisons
Mechanical Philosophy, for a full explanation of the theory of Boscovich.)
The view entertained by Dr. Faraday, which will be comprehended from one or
two short extracts from his valuable and suggestive paper, claims attention:—
“If the view of the constitution of matter already referred to be assumed to be
correct—and I may be allowed to speak of the particles of matter, and the space
between them (in water, or in the vapour of water, for instance), as two different
things—the space must be taken as the only continuous part, for the particles are
considered as separated by space from each other. Space will permeate all
masses of matter in every direction like a net, except that in the place of meshes
it will form cells, isolating each atom from its neighbours, and itself only being
continuous.”
Examining the question of the conducting power of different bodies, and
observing that as space is the only continuous part, so space, according to the
received view of matter, must be at one time a conductor, at others a non-
conductor, it is remarked:
“It would seem, therefore, that, in accepting the ordinary atomic theory, space
may be proved to be a non-conductor in non-conducting bodies, and a conductor
in conducting bodies; but the reasoning ends in this—a subversion of that theory

altogether; for, if space be an insulator, it cannot exist in conducting bodies; and
if it be a conductor, it cannot exist in insulating bodies.”—A Speculation
touching Electric Conduction, and the Nature of Matter: by Michael Faraday,
D.C.L., F.R.S., &c.: Philosophical Magazine, vol. xxiv. Third Series.
See also Wollaston, On the Finite Extent of the Atmosphere.—Phil. Trans. 1822.
Young, On the Essential Properties of Matter.—Lectures on Natural Philosophy.
Mossotti, On Molecular Action.—Scientific Memoirs, vol. i. p. 448.

CHAPTER II.
MOTION.
Are the Physical Forces modes of Motion?—Motion defined—
Philosophical Views of Motion, and the Principles to which
it has been referred—Motions of the Earth and of the Solar
System—Visible Proofs of the Earth’s Motion on its Axis—
Influence of the proper Motions of the Earth on the
Conditions of Matter—Theory of the Conversion of Motion
into Heat, &c.—The Physical Forces regarded as principles
independent of Motion, although the Cause and often
apparently the Effects of it.

Many of the most eminent thinkers of the present time are disposed to
regard all the active principles of nature as “modes of motion,”—to look
upon light, heat, electricity, and even vital force, as phenomena resulting
from “change of place” among the particles of matter; this change,
disturbance, or motion, being dependent upon some undefined mover.[2]
The habit of leaving purely inductive examination for the delusive charms
of hypothesis—of viewing the material world as a metaphysical bundle of
essential properties, and nothing more—has led some eminent philosophers
to struggle with the task of proving that all the wonderful manifestations of
the great physical powers of the universe are but modifications of motion,
without the evidence of any antecedent force.[3]
The views of metaphysicians regarding motion involve many subtle
considerations which need not at present detain us. We can only consider
motion as a change of place in a given mass of matter. Now matter cannot
effect this of itself, no change of place being possible without a mover; and,
consequently, motion cannot be a property of matter, in the strict sense in
which that term should be accepted.[4]

Motion depends upon certain external disturbing and directing forces acting
upon all matter; and, consequently, as every mode of action is determined
by some excitement external to the body moved, motion cannot,
philosophically, be regarded otherwise than as a peculiar affection of matter
under determinable conditions. “We find,” says Sir Isaac Newton, “but little
motion in the world, except what plainly flows from either the active
principles of nature, or from the command of the willer.”[5]
Plato, Aristotle, and the Pythagoreans, supposed that throughout all nature
an active principle was diffused, upon which depended all the properties
exhibited by matter. This is the same as the “plastic nature” of Cudworth,[6]
the “intellectual and artificial fire” of Bishop Berkeley;[7] and to these all
modes of motion were referred. Sir Isaac Newton also regards the material
universe and its phenomena as dependent upon “active principles”—for
instance, the cause of gravity—whereby the planets and comets preserve
their motions in their orbits, and all bodies acquire a degree of motion in
falling; and the cause of fomentation—whereby the heart and blood of
animals preserve a perpetual warmth and motion—the inner parts of the
earth are kept constantly warmed—many bodies burn and shine—and the
sun himself burns and shines, and with his light warms and cheers all
things.
The earth turns on its axis at the rate of more than 1,000 miles an hour, and
passes around the sun with the speed of upwards of 68,000 miles in the
same time.[8] The earth and the other planets of our system move in ellipses
around a common centre: therefore their motion cannot have been
originally communicated merely by the impressed force of projection. Two
forces, at least, must have operated, one making the planets tend directly to
the centre, and the other impelling them to fly off at a tangent to the curve
described. Here we have a system of spheres, held by some power to a great
central mass, around which they revolve with a fearful velocity. Nor is this
all; the Solar System itself, bound by the same mystic chain to an
undiscovered centre, moves towards a point in space at the rate of
33,550,000 geographical miles, whilst our earth performs one revolution
around the sun.[9]
The evidence of the motion of the Earth around its axis, as afforded by the
swinging of a pendulum or the rotation of a sphere, is too interesting to be

omitted. In mechanical philosophy, we have two terms of the same general
meaning—the conservation of the plane of vibration—and the conservation
of the axis of rotation. For the non-scientific reader, these terms require
explanation, and in endeavouring to simplify this as much as possible, we
must ask the indulgence of the Mechanical Philosopher. Let us fix in the
centre of a small round table an upright rod, having an arm extending from
its top, to which we can suspend a tolerably heavy weight attached to a
string. This is our piece of apparatus: upon the table draw a chalk line,
along which line we intend our pendulum to swing, and continuing this line
upon the floor, or by a mark on the wall, our arrangements are complete.
Raise steadily the bob of our pendulum, and set it free, so that its plane of
vibration is along the line which has been marked. As the pendulum is
swinging firmly along this line, slowly and steadily turn the table round. It
will then be seen that the pendulum will still vibrate in the direction of the
line we have continued onward to the wall, but that the line on the table is
gradually withdrawn from it. If we had no upright, we might turn the table
entirely round, without in the slightest degree altering the line along which
the pendulum performs its oscillations. Now, if from some elevated spot,
say, from the centre of the dome of St. Paul’s, a long and heavy pendulum is
suspended, and if on the floor we mark the line along which we set the
pendulum free to vibrate, it will be seen, as in the experiment with the table,
that the marked line moves away from under the pendulum. It continues to
vibrate in the plane it first described, although the line on the earth’s surface
continues to move forward by the diurnal rotation around the axis. Similar
to this is the law of the conservation of the axis of rotation. If a common
humming-top, the spindle of which is its axis of rotation, is set spinning
obliquely, it will be seen that the axis will continue to point along the line it
took at the commencement of motion. By placing a heavy sphere in a lathe,
resting its projecting axial points on some moveable bearings, and then
getting the sphere into extremely rapid motion, one of the bearings may be
removed without the mass falling to the ground. The rapidity of motion
changes so constantly and quickly the position of the particles which have a
tendency to fall, that we have motion balanced against the force of
gravitation in a striking manner; and we learn, from this experiment, the
explanation of the planetary and stellar masses revolving on their axis at a
speed sufficient to maintain them without support in space. A mass of
matter, a sphere or a disc, carefully balanced, is fixed in gymbals such as we

employ for fixing our compass needles, and it is set by some mechanical
contrivance in rapid rotation. The position of the axis of rotation remains
unaltered, although the earth is moving; and thus, by this instrument,—
called the gyroscope,—we can determine, as with the pendulum, the motion
of the earth around its axis; and we learn why, during its movement around
the sun, its axis is undeviatingly pointed towards one point in space, marked
in our Heavens as the Polar Star.
In addition to these great rotations, the earth is subjected to other motions,
as the precession of the equinoxes and the nutation of its axis. Rocking
regularly upon a point round which it rapidly revolves, whilst it progresses
onward in its orbit, like some huge top in tremulous gyration upon the deck
of a vast aërial ship gliding rapidly through space, is the earth performing
its part in the great law of motion.
The rapidity of these impulses, supposing the powers of the physical forces
were for a moment suspended, would be sufficient to scatter the mass of our
planet over space as a mere star-dust.
Limiting, as much as possible, the view which opens upon the mind as we
contemplate the adjustments by which this great machine, our system, is
preserved in all its order and beauty, let us forget the great movement of the
whole through space, and endeavour to consider the effect of those motions
which are directly related to the earth, as a member of one small group of
worlds.
We cannot for a moment doubt, although we have not any experimental
proof of the fact, that the proper motions of the earth materially influence
the conditions of the matter of which it is formed. Every pair of atoms is,
like a balance, delicately suspended, under the constant struggle which
arises from the tendency to fly asunder, induced by one order of forces—
centrifugal force—and the efforts of others, gravitation and cohesion, to
chain them together. The spring is brought to the highest state of tension—
one tremor more, and it would be destroyed.
We cannot, by any comparison with the labours of the most skilful human
artisan, convey an idea of the exquisite perfection of planetary mechanics,
even so far as they have been discovered by the labours of science; and we
must admit that our insight into the vast machinery has been very limited.

All we know is the fact that this planet moves in a certain order, and at a
fixed rate, and that the speed is of itself sufficient to rend the hardest rocks;
yet the delicate down which rests so lightly upon the flower is undisturbed.
It is, therefore, evident that matter is endued with powers, by which mass is
bound to mass, and atom to atom; these powers are not the results of any of
the motions which we have examined, but, acting in antagonism to them,
they sustain our globe in its present form.
Are there other motions to which these powers can be referred? We know of
none. That absolute rest may not exist among the particles of matter is
probable. Electrical action, chemical power, crystalline aggregation, the
expansive force of heat, and many other known agencies, are in constant
operation to prevent it. It must, however, be remembered, that each and
every atom constituting a mass may be so suspended between the balanced
forces, that it may be regarded as relatively at rest.
Theory imagines Motion as producing Force—a body is moved, and its
mere mechanical change of place is regarded as generating heat; and hence
the refinements of modern science have advanced to the conclusion that
motion and heat are convertible. Admitting that the material atoms of which
this world is formed are never in a state of quiescence, yet we cannot
suppose any gross ponderable particle as capable of moving itself; but once
set in motion, it may become the secondary cause of motion in other
particles.[10] The difficulties of the case would appear to have been as
follows:—Are heat, light, electricity, &c., material bodies? If they are
material bodies—and heat, for example, is the cause of motion—must not
the calorific matter move itself—or if it be not self-moving, by what is it
moved? If heat is material, and the primary cause of motion, then matter
must have an innate power of moving; it can convert itself into active force,
or be at once a cause and an effect, which can scarcely be regarded as a
logical deduction.
We move a particle of matter, and heat is manifested; the force being
continued, light, electricity, and chemical action result; all, as appears from
a limited view of the phenomena, arising out of the mechanical force
applied to the particle first moved.[11] This mechanical force, it must be
remembered, is external to the body moved, and is, in all probability, set up
by the movement of a muscle, acted upon by nerves, under the influence of
a will.

The series of phenomena we have supposed to arise admit of an explanation
free of the hypothesis of motion, and we avoid the dangerous ground of
metaphysical speculation, and the subtleties of that logic which rests upon
the immateriality of all creation. This explanation, it is freely admitted, is
incomplete: we cannot distinctly correlate each feature of the phenomena,
combine link to link, and thus form a perfect chain; but it is sufficiently
clear to exhibit what we do know, and leave the unknown free for unbiassed
investigation.
Each particle, each atom of that which conveys to our senses the only ideas
we have of natural objects—ponderable matter—is involved in, or
interpenetrated by, those principles which we call heat and electricity, with
probably many others which are unknown to us; and although these
principles or powers are, according to some law, bound in statical
equilibrium to inert matter, they are freely developed by an external
excitement, and the disturbance of any one of them, upsetting the
equilibrium, leaves the other power equally free to be brought under the
cognizance of human sense by their effects.
When we come to an examination of the influences exerted by these powers
upon the physical earth, the position, that they must be regarded as the
causes of motion rather than the effects of it, will be further considered. At
present it is only necessary to state thus generally the views we entertain of
the conditions of matter in connection with the imponderable forces and
mechanical powers. The conversion, as it has been called, of motion into
heat, in the experiments of Count Rumford and Mr. Joule,[12] are only
evidences that a certain uniformity exists between the mechanical force
applied, and the amount of heat liberated. It does not appear that we have
any proof of the conversion of motion into physical power.
It is necessary, to a satisfactory contemplation of the wonderful properties
of matter, and of the forces regulating the forms of the entire creation, that
we should be content with regarding the elementary bodies which chemistry
instructs us form our globe, as tangible, ponderable atoms, having specific
and distinguishing properties. That we should, as far as it is possible for
finite minds to do so, endeavour to conceive the powers or forces—
gravitation, molecular attraction, electricity, heat, light, and the principle
which determines all chemical phenomena—as manifestations of agencies
which hold a place between the most subtile form of matter and the hidden

principles of vitality, which is still vastly inferior to the spiritual state,
which reveals itself dimly in psychological phenomena, and arrives at its
sublimity in the God of the universe.

FOOTNOTES:
[2] “Motion, therefore, is a change of rectilinear distance between two points.
Allowing the accuracy of this definition, it appears that two points are necessary
to constitute motion; that in all cases, when we are inquiring whether or no any
body or point is in motion, we must recur to some other point which we can
compare with it; and that if a single atom existed alone in the universe, it could
neither be said to be in motion nor at rest.
“The space which we call quiescent is in general the earth’s surface; yet we well
know, from astronomical considerations, that every point of the earth’s surface is
perpetually in motion, and that in very various directions: nor are any material
objects accessible to our senses which we can consider as absolutely motionless,
or even as motionless with regard to each other; since the continual variation of
temperature to which all bodies are liable, and the minute agitations arising from
the motion of other bodies with which they are connected, will always tend to
produce some imperceptible changes in their distances.”—Lectures on Natural
Philosophy, &c., by Thomas Young, M.D. Edited by the Rev. P. Kelland. 1845.
[3] “The position which I seek to establish in this essay is, that the various
imponderable agencies, or the affections of matter which constitute the main
objects of experimental physics, viz., heat, light, electricity, magnetism,
chemical affinity, and motion, are all correlative, or have a reciprocal
dependence;—that neither, taken abstractedly, can be said to be the essential or
proximate cause of the others; but that either may, as a force, produce, or be
convertible into, the other:—thus heat may mediately or immediately produce
electricity, electricity may produce heat, and so of the rest.... Although strongly
inclined to believe that the five other affections of matter, which I have above
named, are, and will ultimately be, resolved into modes of motion, it would be
going too far at present to assume their identity with it: I, therefore, use the term
force, in reference to them, as meaning that active force inseparable from matter,
which induces its various changes.”—On the Correlation of Physical Forces, by
W. R. Grove, Esq., M.A., F.R.S.
[4] When discussing the hypothesis of Hobbes—that no body can possibly be
moved but by a body contiguous and moved—Boyle asks:—
“I demand how there comes to be local motion in the world? For either all the
portions of matter that compose the universe have motion belonging to their
natures, which the Epicureans affirmed for their atoms, or some parts of matter
have this motive power, and some have not, or else none of them have it; but all
of them are naturally devoid of motion. If it be granted that motion does

naturally belong to all parts of matter, the dispute is at an end, the concession
quite overthrowing the hypothesis.
“If Mr. Hobbes should reply that the motion is impressed upon any of the parts
of matter by God, he will say that which I most readily grant to be true, but will
not serve his turn, if he would speak congruously with his own hypothesis. For I
demand whether this Supreme Being that the assertion has recourse to, be a
corporeal or an incorporeal substance? If it be the latter, and yet the efficient
cause of motion in bodies, then it will not be universally true that whatever body
is moved is so by a body contiguous and moved. For, in our supposition, the
bodies that God moves, either immediately or by the intervention of any other
immaterial being, are not moved by a body contiguous, but by an incorporeal
spirit.”—Some Considerations about the Reconcileableness of Reason and
Religion: Boyle, vol. iii. p. 520.
[5] Boyle has some ingenious speculations on this point:—
“That there is local motion in many parts of matter is manifest to sense, but how
matter came by this motion was of old, and is still, hotly disputed of: for the
ancient Corpuscularian philosophers (whose doctrine in most other points,
though not in all, we are the most inclinable to), not acknowledging an author of
the universe, were thereby reduced to make motion congenite to matter, and
consequently coeval with it. But since local motion, or an endeavour at it, is not
included in the nature of matter, which is as much matter when it rests as when it
moves; and since we see that the same portion of matter may from motion be
reduced to rest, and after it hath continued at rest, so long as other bodies do not
put it out of that state, may by external agents be set a moving again; I, who am
not wont to think a man the worse naturalist for not being an atheist, shall not
scruple to say with an eminent philosopher of old, whom I find to have proposed
among the Greeks that opinion (for the main) that the excellent Des Cartes has
revived amongst us, that the origin of motion in matter is from God; and not
only so, but that thinking it very unfit to be believed, that matter barely put into
motion, and then left to itself, should casually constitute this beautiful and
orderly world; I think also further, that the wise Author of things did, by
establishing the laws of motion among bodies, and by guiding the first motions
of the small parts of matter, bring them to convene after the manner requisite to
compose the world; and especially did contrive those curious and elaborate
engines, the bodies of living creatures, endowing most of them with the power of
propagating their species.”—Considerations and Experiments touching the
Origin of Forms and Qualities: Boyle’s Works, vol. ii. p. 460. Edinburgh. 1744.
[6] Cudworth’s Intellectual System.
[7] “According to the Pythagoreans and Platonists, there is a life infused
throughout all things ... an intellectual and artificial fire—an inward principle,
animal spirit, or natural life, producing or forming within, as art doth without—
regulating, moderating, and reconciling the various motions, qualities, and parts
of the mundane system. By virtue of this life, the great masses are held together
in their ordinary courses, as well as the minutest particles governed in their
natural motions, according to the several laws of attraction, gravity, electricity,
magnetism, and the rest. It is this gives instincts, teaches the spider her web, and
the bee her honey;—this it is that directs the roots of plants to draw forth juice
from the earth, and the leaves and the cortical vessels to separate and attract such

particles of air and elementary fire as suit their respective natures.”—Bishop
Berkeley, Siris, No. 277.
[8] “The revolution of the earth is performed in a natural day, or, more strictly
speaking, once in 23h. 56' 4", and as its mean circumference is 24,871 miles, it
follows that any point in its equatorial surface has a rotatory motion of more
than 1,000 miles per hour. This velocity must gradually diminish to nothing at
either pole. Whilst the earth is thus revolving on its axis, it has a progressive
motion in its orbit. If we take the length of the earth’s orbit at 630,000,000, its
motion through space must exceed 68,490 miles in the hour.”—Enc. Brit. art.
Physical Geography.
[9] “Here then we have the splendid result of the united studies of MM.
Argelander, O. Struve, and Peters, grounded on observations made at the three
observatories of Dorpat, Abo, Pulkova, and which is expressed in the following
thesis:—The motion of the solar system in space is directed to a point of the
celestial vault situated on the right line which joins the two stars π and μ
Herculis, at a quarter of the apparent distance of these stars, reckoning from π
Herculis. The velocity of this motion is such, that the sun, with all the bodies
which depend upon it, advances annually in the above direction 1·623 times the
radius of the earth’s orbit, or 33,550,000 geographical miles. The possible error
of this last number amounts to 1,733,000 geographical miles, or to a seventh of
the whole value. We may then wager 400,000 to 1 that the sun has a proper
progressive motion, and 1 to 1 that it is comprised between the limits of thirty-
eight and twenty-nine millions of geographical miles.”—Etudes d’Astronomie
Stellaire: Sur la Voie Lactée et sur les Distances des Etoiles Fixes: M. F. W. G.
Struve. [A report addressed to his Excellency M. Le Comte Ouvaroff; Minister
of Public Instruction and President of the Imperial Academy of Sciences at St.
Petersburg.]
[10] “The first great agent which the analysis of natural phenomena offers to our
consideration, more frequently and prominently than any other, is force. Its
effects are either, 1st, to counteract the exertion of opposing force, and thereby
to maintain equilibrium; or, 2ndly, to produce motion in matter,
“Matter, or that whatever it be of which all the objects in nature which manifest
themselves directly to our senses consist, presents us with two general qualities,
which at first sight appear to stand in contradiction to each other—activity and
inertness. Its activity is proved by its power of spontaneously setting other
matter in motion, and of itself obeying their mutual impulse, and moving under
the influence of its own and other force; inertness, in refusing to move unless
obliged to do so by a force impressed externally, or mutually exerted between
itself and other matter, and by persisting in its state of motion or rest unless
disturbed by some external cause. Yet, in reality, this contradiction is only
apparent. Force being the cause, and motion the effect produced by it on matter,
to say that matter is inert, or has inertia, as it is termed, is only to say that the
cause is expended in producing its effect, and that the same cause cannot
(without renewal) produce double or triple its own proper effect. In this point of
view, equilibrium may be conceived as a continual production of two opposite
effects, each, undoing at every instant what the other has done,”?—See
continuation of the argument in Herschel’s Discourse on the Study of Natural
Philosophy, page 223.

In the Edinburgh New Philosophical Journal, vol. xlv., will be found a paper by
Dr Robert Brown—“Of the sources of motions upon the Earth, and of the means
by which they are sustained,” which will well repay an attentive perusal, as
pointing to a class of investigation of the highest order, and containing
deductions of the most philosophic description.
[11] Friction, it is well known, generates heat; by rapidly rubbing two sticks
together, the Indian produces their ignition; heat and light being both manifested.
Under every mechanical disturbance electrical changes can be detected, and the
action of heat in the combustion of the wood is a chemical phenomenon.
[12] Count Rumford’s experiment consisted in placing a mass of metal in a box
of water at a known temperature, and, by employing a boring apparatus,
ascertaining carefully the increase of heat after a given number of revolutions.
He thus describes his most satisfactory experiment:—
“Everything being ready, I proceeded to make the experiment I had projected, in
the following manner. The hollow cylinder having been previously cleaned out,
and the inside of its bore wiped with a clean towel till it was quite dry, the square
iron bar, with the blunt steel borer fixed to the end of it, was put into its place;
the mouth of the bore of the cylinder being closed at the same time by means of
the circular piston through the centre of which the iron bar passed.
“This being done, the box was put in its place; and the joinings of the iron rod,
and of the neck of the cylinder with the two ends of the box, having been made
water-tight, by means of collars of oiled leather, the box was filled with cold
water (viz., at the temperature of 60°) and the machine was put in motion. The
result of this beautiful experiment was very striking, and the pleasure it afforded
me amply repaid me for all the trouble I had had, in contriving and arranging the
complicated machinery used in making it. The cylinder, revolving at the rate of
about thirty-two times in a minute, had been in motion but a short time, when I
perceived, by putting my hand into the water and touching the outside of the
cylinder, that heat was generated, and it was not long before the water which
surrounded the cylinder began to be sensibly warm. At the end of one hour, I
found, by plunging a thermometer into the water in the box (the quantity of
which fluid amounted to 18·77 lbs. avoirdupois, or 2–1/4 wine gallons), that its
temperature had been raised no less than 47°; being now 107° of Fahrenheit’s
scale. When thirty minutes more had elapsed, or one hour and thirty minutes
after the machinery had been put in motion, the heat of the water in the box was
142°. At the end of two hours, reckoning from the beginning of the experiment,
the temperature of the water was found to be raised to 178°. At two hours twenty
minutes it was at 200°; and at two hours thirty minutes it actually boiled.”—
Inquiry concerning the Source of the Heat excited by Friction: Philosophical
Transactions, vol. lxxxviii. a.d. 1798.
“Mr. Joule brought a communication on the same subject before the British
Association at Cambridge, which was afterwards published in the Philosophical
Magazine, and from that journal the following notices are extracted:—
“The apparatus exhibited before the Association consisted of a brass paddle-
wheel, working horizontally in a can of water. Motion could be communicated to
this paddle by means of weights, pulleys, &c. The paddle moved with great
resistance in the can of water, so that the weights (each of four pounds)
descended at the slow rate of about one foot per second. The height of the

pulleys from the ground was twelve yards, and consequently when the weights
had descended through that distance they had to be wound up again in order to
renew the motion of the paddle. After this operation had been repeated sixteen
times, the increase of the temperature of the water was ascertained by means of a
very sensible and accurate thermometer.
“A series of nine experiments was performed in the above manner, and nine
experiments were made in order to eliminate the cooling or heating effects of the
atmosphere. After reducing the result to the capacity for heat of a pound of
water, it appeared that for each degree of heat evolved by the friction of water, a
mechanical power equal to that which can raise a weight of 890 lbs. to the height
of one foot, had been expended.
“Any of your readers who are so fortunate as to reside amid the romantic
scenery of Wales or Scotland could, I doubt not, confirm my experiments by
trying the temperature of the water at the top and at the bottom of a cascade. If
my views be correct, a fall of 817 feet will of course generate one degree of heat,
and the temperature of the river Niagara will be raised about one fifth of a
degree by its fall of 160 feet.”—Relation between Heat and Mechanical Power:
Philosoph. Mag. vol. xxvii. 1845.

CHAPTER III.
GRAVITATION.
The Forms of Matter—Shape of the Earth—Probability of the
Mass forming this Planet having existed in a Nebulous State
—Zodiacal Lights—Comets—Volatilization of Solid Matter
by Artificial means—The principle of Gravitation—Its
Influence through Space and within the smallest Limits—
Gravitating powers of the Planets—Density of the Earth—
Certainty of Newton’s Law of the Inverse Square—
Discovery of Neptune—State of a Body relieved from
Gravitation—Experiment explaining Saturn’s Ring, &c.—
General inference.

Let us suppose the earth—consisting of three conditions of matter; the
solid, the fluid, and the aëriform—to be set free from that power by which it
is retained in its present form of a spheroid flattened at the poles, but still
subject to the influences of its diurnal and annual rotations. Agreeably to the
law which regulates the conditions of all bodies moving at high velocities,
the consequence of such a state of things would be, that our planet would
instantly spread itself over an enormous area. The waters and even the solid
masses of this globe would, in all probability, present themselves amidst the
other phenomena of space in a highly attenuated state, revolving in an orbit
around the sun, as a band of nebulous matter, which might sometimes be
rendered sensible to sight by still reflecting solar light, or by condensation
in the form of flights of shooting stars.[13]
This may be illustrated by experiment. If upon a rapidly revolving disc we
place a ball of dust, it will be almost immediately spread out, and its
particles will arrange themselves in a series of regular curves, varying with
the velocity of the motion. In addition to the disintegration which would
arise from the tendency of the atoms to fly from the centre, the motion, in
space, of the planetary mass would naturally occasion a trailing out, and the
only degree of uniformity which this orb could, under these imaginary

conditions, possibly present, would be derived from the combined effects of
motions in different directions.
Amid the remoter stars, some remarkable cloud-like appearances are
discovered. These nebulæ, presenting to the eye of the observer only a
gleaming light, as from some phosphorescent vapour, were long regarded as
indications of such a condition as that which we have just been considering.
Astronomers saw, in those mysterious nebulæ, a confirmation of their
views, which regarded all the orbs of the firmament as having once been
thin sheets of vapour, which had gradually, from irregular bodies traversing
space, been slowly condensed about a centre, and brought within the limits
of aggregating agencies, until, after the lapse of ages, they become sphered
stars, moving in harmony amid the bright host of heaven.[14] Geologists
seized on those views with eagerness, as confirming theoretical conclusions
deduced from an examination of the structure of the earth itself, and
explained by them the gradual accretion of atoms into crystalline rocks
from a cooling mass.
The researches of modern astronomers, aided by the magnificent
instruments of Lord Rosse,[15] have, however, shown that many of the most
remarkable nebulæ are only clusters of stars; so remote from us, that the
light from them appears blended into one diffused sheet or luminous film.
There are, however, the Magellanic clouds, and other singular patches of
light, exhibiting changes which can only be explained on the theory of their
slow condensation. There is no evidence to disprove the position that world-
formation may still be going on; that a slow and gradual aggregation of
particles, under the influence of laws with which we are acquainted, may be
constantly in progress, to end, eventually, in the formation of a sphere.
May we not regard the zodiacal light as the remains of a solar luminiferous
atmosphere, which once embraced the entire system of which it is the
centre?[16] Will not the strange changes which have been seen to take place
in cometary bodies, even whilst they were passing near the earth,—as the
division of Biela’s comet and the ultimate formation of a second nucleus
from the detached portion,—strongly tend to support the probability of the
idea that attenuated matter has, in the progress of time, been condensed into
solid masses, and that nebulous clouds must still exist in every state of
tenuity in the regions of infinite space,[17] which, in the mysterious

processes of world-formation, will, eventually, become stars, and reflect
across the blue immensity of heaven, in brightness, that light which is the
necessary agent of organisation and all manifestations of beauty?
The inferences drawn from a careful study of the condition of our own
globe are in favour of the assumption of the existence of nebulous matter.
By the processes of art and manufacture, by the operation of those powers
on which organisation and life depend, solid matter is constantly poured off
in such a state that it cannot be detected, as matter, by any of the human
senses. Yet a thousand results, daily and hourly accumulating as truths
around us, prove that the solid metals, the gross earths, and the constituents
of animal and vegetable life, all pass away invisible to us, and become “thin
air.” We know that, floating around us, these volatilized bodies exist in
some material form, and numerous experiments in chemistry are calculated
to convince us, that the most attenuated air is capable, with a slight change
of circumstances, of being converted into the condition of solid masses.
Hydrogen gas, the lightest, the most ethereal of the chemical elements,
dissolves iron and zinc, arsenic, sulphur, and carbon; and from the
transparent combinations thus formed, we can with facility separate those
ponderous bodies. Such substances must exist in our own atmosphere; why
not in the regions of space? Whether this planet ever floated a mass of
nebulous matter, only known by its dim and filmy light, or comet-like
rushed through space with widely eccentric orbit, are questions which can
only receive the reply of speculative minds. Whether the earth and the other
members of the Solar System were ever parts of a Central Sun,[18] and
thrown from it by some mighty convulsion, though now revolving with all
the other masses around that orb, chained in their circuits by some infinite
power, is beyond the utmost refinements of science to discover. This
hypothesis is, however, in its sublime conception, worthy of the master-
mind that gave it birth.
All we know is, that our earth is an oblate sphere, which, by the effects of
its rotation around an axis, is somewhat enlarged at the equator and
flattened at the poles;—that it maintains its regular course around the sun,
in virtue of the operation of two forces, one of which, acting constantly,
would eventually draw it into the body of the sun itself; but that it is
opposed by the other, centrifugal force, and the varying momentum of the
revolving mass;—that the same force acting from the centre of the earth

itself, and from the centre of every particle of its substance, resolves the
whole into a globular form.
The principle of Gravitation[19] is that force which resides in every form of
matter, by which particle is attracted by particle, and mass by mass, the less
towards the greater. What this may be, we scarcely dare to speculate. In the
vast area of its action, which opens before the eye of the mind, we see a
power spanning all space, and linking together every one of those myriads
of worlds which spangle the robe of the Infinite, and we are compelled to
pause. Is this principle of gravitation a property of matter, or is it a power
higher than the more tangible forces, is the question which presses on the
mind. If we regard it as a subtile principle pervading all space, we compel
ourselves to look beyond it for another power yet more refined; and we
cannot halt until, ascending from the limitable to the illimitable, we resolve
gravitation and its governing influences to the centre of all power—the will
of the eternal Creator.
Science has developed the grand truth, that it is by the exercise of this all-
pervading influence that the earth is retained in its orbit—that the pellucid
globe of dew which glistens on the leaf is bound together—that the débris
which float upon the lake accumulate into one mass—that the sea exhibits
the phenomena of the tides—and the aërial ocean its barometric changes. In
all things this force is active, and throughout nature it is ever present. Our
knowledge of the laws which it obeys, enables us to conclude that the sun
and distant planets are consolidated masses like this earth. We find that they
have gravitating power, and by comparing this influence with that exerted
by the earth, we are enabled to weigh the mass of one planet against
another. In the balance of the astronomer, it is as easy to poise the remote
star, as it is for the engineer to calculate the weight of the iron tunnel of the
Menai Straits, or any other mechanical structure. Thus throughout the
universe the balance of gravitating force is unerringly sustained. If one of
the most remote of those gems of light, which flicker at midnight in the
dark distance of the starry vault, was, by any power, removed from its
place, the disturbance of these delicately balanced mysteries would be felt
through all the created systems of worlds.
From the peculiarity of the laws which this power called gravity obeys, it
has been inferred that it acts from centres of force; it is proved that its
power diminishes in the inverse ratio of the square of the distance, and that

the gravitating power of every material body is in the direct proportion of
its mass. In astronomical calculations we have first to learn the mass of our
earth. Experiment informs us that the density of our hardest rock is not
above 2·8; but from the enormous pressure to which matter must be
subjected, at great depths from the surface, the weight of the
superincumbent mass constantly increasing, it is quite certain that the
earth’s density must be far more than this. Maskelyne determined the
attraction of large masses by a plummet and line on the mountain
Schehallion.[20] Cavendish, with exceedingly delicate apparatus, observed
the attraction of masses of known weight and size upon each other.
Applying the powers of arithmetical calculation, and the data obtained from
the small experiments to the larger phenomena, Maskelyne determined the
earth’s mean density to be 4·71, whilst Cavendish made it 5·48, but the
more recent refined investigations of Baily have determined it to be 5·67.
[21]

From data thus obtained by severe inductive experiments and mathematical
analyses, the astronomer, by observing the deviations of a distant star, is
enabled to determine the influence of those stellar bodies near which it
passes, and, hence, to calculate the relative magnitudes of each. The
accuracy of the law is in this way put to the severest test, and the precision
of astronomical prediction is the strongest proof of its universality and
truth.
Rolling onward its lonely way, in the far immensity of our system, the
planet Uranus was discovered by the elder Herschel,—so great its distance
that its diminished light could scarcely be detected by the most powerful
telescopes; but since its discovery its path has been carefully watched, and
some irregularities noticed. Most of these disturbances were referable to
known causes; but a little alteration in its rate of motion observed when the
planet was in one portion of its vast orbit was unexplained. Convinced of
the certainty of Newton’s law, and having determined that the attraction of
known masses was insufficient to produce the disturbance observed, these
deviations were referred to the gravitating influence of a mass beyond the
known limits of our Solar System. By the investigations of Adams in
England,[22] and Le Verrier in France,[23] the place of the hypothetical mass
was determined, and its size computed. As a grand confirmation of the great
law, and to the glory of those two far-searching minds, who do honour to

their respective countries and their age, the hypothesis became a fact, in the
discovery of the planet Neptune in the place determined by rigorous
calculation. Astronomy affords other examples of the sublime truth of the
law of gravitation, than which science can afford no more elevated poetry.
So completely is all nature locked in the bonds of this infinite power, that it
is no poetic exaggeration to declare, that the blow which rends any earthly
mass is conveyed by successive impulses to every one of the myriads of
orbs, which are even too remote for the reach of telescopic vision.
An illustrative experiment must close our consideration of relative
operations of rotation and gravitation. We well know that a body in a fluid
state would, if suspended above the earth, it being at the same time free to
take any form, naturally assume that of a flattened spheroid, from the action
of the mass of the earth upon it: whereas the force of cohesive attraction
acting equally from all sides of a centre, would, if uninfluenced, necessarily
produce a perfect sphere. The best method of showing that this would be the
case, is as follows:—
Alcohol and water are to be mixed together until the fluid is of the same
specific gravity as olive oil. If, when this is effected, we drop globules of
the oil into the mixed fluid, it will be seen that they take an orbicular form;
—and, of course, in this experiment the power of the earth’s gravitating
influence is neutralized. The same drops of oil under any other conditions
would be flattened. Simple as this illustration is, it tells much of the
wondrous secret of those beautifully balanced forces of cohesion and of
gravitation; and from the prosaic fact we rise to a great philosophical truth.
Our experiment may lead us yet farther in exemplification of known
phenomena. If we pass a steel wire through one of those floating spheres of
oil, and make it revolve rapidly and steadily, thus imitating the motion of a
planet on its axis, the oil spreads out, and we have the spheroidal form of
our earth. Increase the rapidity of this rotation, and when a certain rate is
obtained the oil widens into a disc, a ring separates itself from a central
globe, and at a distance from it still revolves around it.[24] Here we have a
miniature representation of the ring of Saturn. This is a suggestive
experiment, the repetition of which, by reflective minds, cannot fail to lead
to important deductions. The phenomena of cohesion, of motion, and
gravitation, are all involved; and we produce results resembling, in a
striking manner, the conditions which prevail in the planetary spaces, under

the influence of the same powers. If we take a glass globe, and having filled
it with a fluid of the proper density, drop into it large and small globules of
oil, we may produce an instructive representation of the stellar vault, with
its beautiful spheres of light revolving in their respective orbits; and though
crossing each other’s paths, still moving in obedience to attracting and
repelling forces—onward in perfect harmony.
From the centre of our earth to the utmost extremity of the universe—from
the infinitely small to the immensely vast—gravitation exerts its force. It is
met on all sides by physical powers acting in antagonism to it, but, like a
ruling spirit, it restrains them in their wildest moods.

The smallest dust which floats upon the wind
Bears this strong impress of the Eternal Mind.
In mystery round it, subtile forces roll;
And gravitation binds and guides the whole.
In every sand, before the tempest hurl’d,
Lie locked the powers which regulate a world,
And from each atom human thought may rise
With might to pierce the mysteries of the skies,—
To try each force which rules the mighty plan,
Of moving planets, or of breathing man;
And from the secret wonders of each sod,
Evoke the truths, and learn the power of God.

FOOTNOTES:
[13] Three hypotheses may be used to account for this most curious
phenomenon.
1st. The body shines by its own light, and then explodes like a sky-rocket,
breaking into minute fragments too small to be any longer visible to the naked
eye.
2nd. Such a body, having shone by its own light, suddenly ceases to be
luminous. “The falling stars and other fiery meteors which are frequently seen at
a considerable height in the atmosphere, and which have received different
names according to the variety of their figure and size, arise from the

fermentation of the effluvia of acid and alkaline bodies which float in the
atmosphere. When the more subtile parts of the effluvia are burned away, the
viscous and earthy parts become too heavy for the air to support, and by their
gravity fall to the earth.”—Keith’s Use of the Globes. According to Sir Humphry
Davy, in the Philosophical Transactions for 1847, “the luminous appearances of
shooting stars and meteors cannot be owing to any inflammation of elastic
fluids, but must depend upon the ignition of solid bodies.”
3. The body shines by the reflected light of the sun, and ceases to be visible by
its passing into the earth’s shadow, or, in other words, is eclipsed. Upon the two
former suppositions the fact of the star’s disappearance conveys to us no
knowledge of its position, or of its distance from the earth; and all that can be
said is, that if it be a satellite of the earth, the great rapidity of its motion
involves the necessity of its being at no great distance from the earth’s surface—
much nearer than the moon; while the resistance it would encounter in traversing
the air would be so great that it is probably without the limits of our atmosphere.
Sir J. W. Lubbock leans to the third hypothesis.—Sir J. W. Lubbock, On
Shooting Stars: Phil. Mag. No. 213, p. 81.
Sir J. Lubbock also published a supplementary paper on the same subject, in No.
214, p. 170.
Mr. J. P. Joule entertains an hypothesis with respect to Shooting Stars similar to
that advocated by Chladni to account for meteoric stones, and he reckons the
ignition of these miniature planetary bodies by their violent collision with our
atmosphere, to be a remarkable illustration of the doctrine of the equivalency of
heat to mechanical power, or vis viva.
If we suppose a meteoric stone of the size of a six-inch cube to enter our
atmosphere at the rate of eighteen miles per second of time, the atmosphere
being 1/100 of its density at the earth’s surface, the resistance offered to the
motion of the stone will in this case be at least 51,600 lbs.; and if the stone
traverse twenty miles with this amount of resistance, sufficient heat will thereby
be developed to give 1° Fahrenheit to 6,967,980 lbs. of water. Of course by far
the largest portion of this heat will be given to the displaced air, every particle of
which will sustain the shock, whilst only the surface of the stone will be in
violent collision with the atmosphere. Hence the stone may be considered as
placed in a blast of intensely heated air, the heat being communicated from the
surface to the centre by conduction. Only a small portion of the heat evolved will
therefore be received by the stone; but if we estimate it at only 1/100 it will still
be equal to 1° Fahrenheit per 69,679 lbs. of water, a quantity quite equal to the
melting and dissipation of any materials of which it may be composed.—Mr. J.
P. Joule, On Shooting Stars: Phil. Mag. No. 216, p. 348.
[14] “Laplace conjectures that in the original condition of the solar system, the
sun revolved upon his axis, surrounded by an atmosphere which, in virtue of an
excessive heat, extended far beyond the orbits of all the planets, the planets as
yet having no existence. The heat gradually diminished, and as the solar
atmosphere contracted by cooling, the rapidity of its rotation increased by the
laws of rotatory motion; and an exterior zone of vapour was detached from the
rest, the central attraction being no longer able to overcome the increased
centrifugal force. This zone of vapour might in some cases retain its form, as we
see it in Saturn’s ring; but more usually the ring of vapour would break into

several masses, and these would generally coalesce into one mass, which would
revolve about the sun,”—Whewell’s Bridgewater Treatise.
The following passage is translated by the same author from Laplace:—
“The anterior state (a state of cloudy brightness) was itself preceded by other
states, in which the nebulous matter was more and more diffuse, the nucleus
being less and less luminous. We arrive in this manner at a nebulosity so diffuse,
that its existence could scarce be suspected. Such is in fact the first state of the
nebula which Herschel carefully observed by means of his telescope.”
Sir William Herschel has the following observations on these remarkable
masses:—
“The nature of planetary nebulæ, which has hitherto been involved in much
darkness, may now be explained with some degree of satisfaction, since the
uniform and very considerable brightness of their apparent disc accords
remarkably well with a much condensed, luminous fluid; whereas, to suppose
them to consist of clustering stars will not so completely account for the
milkiness or soft tint of their light, to produce which it would be required that
the condensation of the stars should be carried to an almost inconceivable degree
of accumulation.
“How far the light that is perpetually emitted from millions of suns may be
concerned in this shining fluid, it might be presumptuous to attempt to
determine; but notwithstanding the inconceivable subtilty of the particles of
light, when the number of the emitting bodies is almost infinitely great, and the
time of the continual emission indefinitely long, the quantity of emitted particles
may well become adequate to the constitution of a shining fluid or luminous
matter, provided a cause can be found that may retain them from flying off, or
reunite them.”—Observations on Nebulous Stars: Philosophical Transactions,
vol. lxxxi. a.d. 1791.
In addition, the following Memoirs on the same subject, by Sir William
Herschel, have been published in the Philosophical Transactions:—Catalogue of
1000 Nebulæ and Clusters of Stars, vol. lxxvi.; Catalogue of another 1000, with
remarks on the Heavens, vol. lxxix.; Catalogue of 500 more, with remarks as
above, vol. xcii.; Of such as have a cometary appearance, vol. ci.; Of planetary
nebulæ, ibid.; Of stellar nebulæ, ibid.; On the sidereal part of the heavens, and
its connection with the nebulous, vol. civ.; On the relative distances of clusters of
nebulous stars, vol. cviii.
[15] Lord Rosse’s beautiful telescopes have been formed upon principles which
appear to embrace the best possible conditions for obtaining a reflecting surface
which should reflect the greatest quantity of light, and retain that property little
diminished for a length of time. The alloy used for this purpose consists of tin
and copper in atomic proportions, namely, one atom of tin to four atoms of
copper, or by weight 58·9 to 126·4.—On the Construction of large Reflecting
Telescopes: by Lord Rosse. Report of the Fourteenth Meeting of the British
Association, 1844, p. 79.
[16] The best description of the Zodiacal Light occurs in a letter furnished by Sir
John Herschel to the Times newspaper in March, 1843:—“The zodiacal light, as
its name imports, invariably appears in the zodiac, or, to speak more precisely, in
the plane of the sun’s equator, which is 7° inclined to the zodiac, and which

plane, seen from the sun, intersects the ecliptic in longitude 78° and 258°, or so
much in advance of the equinoctial points: in consequence it is seen to the best
advantage at, or a little after, the equinoxes; after sunset, at the spring, and
before sunrise, at the autumnal equinox; not only because the direction of its
apparent axis lies at those times more nearly perpendicular to the horizon, but
also because at those epochs we are approaching the situation when it is seen
most completely in section.
“At the vernal equinox the appearance of the zodiacal light is that of a pretty
broad pyramidal, or rather lenticular, body of light, which begins to be visible as
soon as the twilight decays. It is very bright at its lower or broader part near the
horizon, and, if there be broken clouds about, often appears like the glow of a
distant conflagration, or of the rising moon, only less red, giving rise, in short, to
amorphous masses of light such as have been noticed by one of your
correspondents as possibly appertaining to the comet. At higher altitudes, its
light fades gradually, and is seldom traceable much beyond the Pleiades, which
it usually, however, attains and involves, and (what is most to my present
purpose) its axis at the vernal equinox is always inclined (to the northward of the
equator) at an angle of between 60° and 70° to the horizon, and it is most
luminous at its base, resting on the horizon, where also it is broadest, occupying,
in fact, an angular breadth of somewhere about 10° or 12° in ordinary clear
weather.”
[17] “The assumption that the extent of the starry firmament is literally infinite
has been made by one of the greatest of astronomers, the late Dr. Olbers, the
basis of a conclusion that the celestial spaces are, in some slight degree, deficient
in transparency; so that all beyond a certain distance is, and must remain for
ever, unseen; the geometrical progression of the extinction of light far
outrunning the effect of any conceivable increase in the power of our telescopes.
Were it not so, it is argued, every part of the celestial concave ought to shine
with the brightness of the solar disc, since no visual ray could be so directed as
not, in some point or other of its infinite length, to encounter such a disc.”—
Edinburgh Review, p. 185, for January, 1848; Etudes d’Astronomie Stellaire.
[18] In the Astronomische Nachrichten of July, 1846, appeared a Memoir by M.
Mädler, Die Centralsonne. The conclusions arrived at by Mädler may be
understood from the following quotation from a French translation, made by M.
A. Gautier, in the Archives des Sciences Physiques et Naturelles, for October,
1846:—“Quoiqu’il résulte de ce qui précède que la région du ciel que j’ai
adoptée satisfait à toutes les conditions posées plus haut, il n’en est pas moins
convenable de la soumettre à toutes les épreuves possibles. Plusieurs essais de
combinaisons différentes m’ont convaincu qu’on ne pourrait trouver aucun autre
point dans le ciel qui pût tenir lieu, même d’une manière approchée, que celui
que j’ai adopté. On pourrait maintenant m’addresser l’objection que, si la région
du ciel où se trouve le centre de gravité de notre système d’étoiles fixes, est
déterminée par ce qui précède entre certaines limites, il n’en résulte pas la
nécessité de choisir Alcyone pour ce centre, attendu qu’il pourrait bien tomber
sur quelqu’autre étoile située dans le groupe ou dans son voisinage. Mais outre
que c’est tout près de là que se trouve le groupe le plus brillant et le plus riche en
étoiles de tout le ciel, et qu’il ne s’agit point ici d’un point arbitraire situé dans le
voisinage peu apparent et qui n’ait rien qui le distingue, il ne se trouve nul part,
même dans la région voisine, une aussi exacte concordance des mouvements

propres qu’ici, et ces mouvements correspondent mieux que tous les autres aux
conditions établies plus haut. Or si l’on doit considérer ce groupe central, entre
les étoiles également éloignées, on peut présumer que la plus brillante de
beaucoup présente la plus grande masse. Outre cela Alcyone, considérée
optiquement, est au milieu du groupe des Pleïades; et son mouvement propre,
déterminé par Bessel, est plus exactement en accord avec la moyenne de ceux
des autres Pleïades; ainsi que des étoiles de cette région jusqu’à 10° de distance.
Je puis donc établir comme conséquence de tout ce qui précède, que le groupe
des Pleïades est le groupe central de l’ensemble du système des étoiles fixes,
jusqu’aux limites extérieures déterminées par la Voie Lactée; et que Alcyone est
l’étoile de ce groupe qui paraît être, le plus vraisemblablement, le vrai Soleil
central.”
[19] See the article On Gravitation, Penny Cyclopædia, from the pen of the
Astronomer-Royal.
[20] Delambre dates the commencement of modern astronomical observation in
its most perfect form from Maskelyne, who was the first who gave what is now
called a standard catalogue (a.d. 1790) of stars; that is, a number of stars
observed with such frequency and accuracy, that their places serve as standard
points of the heavens. His suggestion of the Nautical Almanack, and his
superintendence of it to the end of his life, from its first publication in 1767, are
mentioned in the Almanack (vol. i. p. 364); his Schehallion Experiment on
Attraction in vol. iii. p. 69; and the character of his Greenwich Observations in
Greenwich Observatory in vol. ii. p. 442.
[21] Experiments to determine the Density of the Earth. By Henry Cavendish,
Esq., F.R.S. and F.A.S.—Philosophical Transactions, 1798.
[22] Adams: An Explanation of the observed irregularities in the motion of
Uranus, on the hypothesis of disturbance caused by a more distant Planet.—
Appendix to Nautical Almanack for 1851.
[23] Le Verrier: Premier Mémoire sur la théorie d’Uranus, Comptes Rendus,
vol. xxi.; Sur la planête qui produit les anomalies observées dans le mouvement
d’Uranus.—Ib. vol. xxiii.
[24] The experiment alluded to is one of a series by M. Plateau, who thus
describes his arrangement of the fluid:—“We begin by making a mixture of
alcohol and distilled water, containing a certain excess of alcohol, so that when
submitted to the trial of the test tube it lets the small sphere of oil fall to the
bottom rather rapidly. When this point is obtained, the whole is thrown upon
filters, care being taken to cover the funnels containing these last with plates of
glass; this precaution is taken in order to prevent, as much as possible, the
evaporation of the alcohol. The alcoholic liquor passes the first through the
filters, ordinarily carrying with it a certain number of very minute spherules of
oil When the greater part has thus passed, the spherules become more numerous;
what still remains in the first filters, namely, the oil and a residue of alcoholic
liquor, is then thrown into a single filter placed on a new flask. This last filtration
takes place much more slowly than the first, on account of the viscosity of the
oil; it is considerably accelerated by renewing the filter once or twice during the
operation. If the funnel has been covered with sufficient care, the oil will collect
into a single mass at the bottom of the flask under a layer of alcoholic liquor.”—
On the Phenomena presented by a free Liquid Mass withdrawn from the action

of Gravity. By Professor Plateau, of the University of Ghent. Translated from the
Memoirs of the Royal Academy of Brussels, vol. xvi.; in the Scientific Memoirs,
vol. iv. part 13.

CHAPTER IV.
MOLECULAR FORCES.
Conditions of Matter—Variety of organized Forms—Inorganic
Forms—All matter reducible to the most simple conditions
—Transmutation, a natural operation—Chemical
Elementary Principles—Divisibility of Matter—Atoms—
Molecules—Particles—Molecular Force includes several
Agencies—Instanced in the Action of Heat on Bodies—All
Bodies porous—Solution—Mixture—Combination—
Centres of Force—Different States of Matter (Allotropic
Conditions)—Theories of Franklin, Æpinus, and Coulomb—
Electrical and Magnetic Agencies—Ancient Notions—
Cohesive Attraction, &c.

In contemplating the works of nature, we cannot but regard, with feelings of
religious admiration, the infinite variety of forms under which matter is
presented to our senses. On every hand the utmost diversity is exhibited;
through all things we trace the most perfect order; and over all is diffused
the charm of beauty. It is the uneducated or depraved alone who find
deformities in the creations by which we are surrounded.
The three conditions of matter are—the solid, the fluid, and the aëriform;
and these belong equally to the organic and the inorganic world.
In organic nature we have an almost infinite variety of animal form,
presenting developments widely different from each other, yet in every case
suited to the circumstances required by the position which the creature,
occupies in the scale of being. Through the entire series, from the Polype to
the higher order of animals, even to man, we find a uniformity in the
progress towards perfection, and a continuity in the series, which betrays
the great secret, that the mystery of life is the same in all,—a pervading
spiritual essence associated with matter, and modifying it by the master-
mechanism of an Infinite mind.

In the vegetable clothing of the surface of the earth, which fits it for the
abode of man and animals—from the confervæ of a stagnant pool, or the
lichen of the wind-beaten rocks, to the lordly oak or towering palm—a
singularly beautiful chain of being presents itself to the contemplative mind,
and we cannot but trace the gradual elevation in the scale of organization.
In the inorganic world, where the great phenomena of life are wanting, we
have constantly exhibited the working of powers of a strangely complicated
kind. The symmetrical arrangement of crystals—the diversified characters
of mineral formations—the systematic aggregations of particles to form
masses possessing properties of a peculiar and striking nature—all prove,
that agencies, which science, with all its refinements, has not yet detected,
are unceasingly at work. Heat, electricity, chemical power—whatever that
may be—and the forces of cohesion, are known to be involved in the
production of the forms we see; but contemplation soon leads to the
conviction that these powers are subordinate to others which we know not
of. We know only the things belonging to the surface of our planet, and
these but superficially. The geologist traces rock-formations succeeding
each other (from the primary strata holding no traces of organized forms,
through the Paleozoic series, in which, step by step, the history of animal
life is recorded,) to the more recent formations, teeming with relics, which,
though allied to some animal types still existing, are generally such as have
passed away. The naturalist searches the earth, the waters, and the air, for
their living things; and the diversity of form, the variety of condition, and
the perfection of organization which he discovers as belonging to this our
epoch—differing from, indeed bearing but a slight relation to, those which
mark the earth’s mutations—exhibit, in a most striking view, the endless
variety of characters which matter can assume.
We are so accustomed to all these phenomena of matter, that it is with some
difficulty we can bend ourselves to the study of the more simple conditions
in which it exists.
The solid crusts of this telluric sphere—the waters and the atmosphere—the
diversified fabrics of the vegetable kingdom—and the still more
complicated structures of men and animals—are, altogether, but the
aggregation of minute particles in accordance with certain fixed laws. By
mechanical means all kinds of matter may be reduced to powder, the fine
particles of which would not appear very different from each other, but each

atom has been impressed with properties peculiar to itself, which man has
no power to change.
To nature alone belongs the mysterious property of transmutation. The
enthusiastic alchemist, by the agency of physical forces, dissipates a metal
in vapour; but it remains a metal, and the same metal still. By the Hermetic
art he breaks up the combination of masses; but he cannot alter the
principles of any one of the elements which form the mass upon which his
skill is tried.
Every atom is invested with properties peculiar to all of its class; and each
one possesses powers, to which in mute obedience it is compelled, by
which these properties are modified, and the character of matter varied.
What are those properties? Do we know anything of those powers?
The earth, so far as we are acquainted with it, is composed of about sixty
principles, which we call elementary. These are the most simple states to
which we can reduce matter, and from them all the forms of creation yet
examined by the chemist are produced. These elementary principles are,
some of them, permanently gaseous under the ordinary temperature, and
others exist as solid masses; the difference between the two conditions
being regulated, as it appears, by the opposing forces of heat and cohesive
attraction.
Matter has been regarded by some as infinitely divisible; but the known
conditions of chemical combinations lead to the conclusion that there are
limits beyond which matter cannot be divided.[25] The theory of atoms
having determinate characters, and possessing symmetric forms, certainly
has the advantage of presenting to the human mind a starting point—a sort
of standing ground,—from which it can direct the survey of cosmical
phenomena. The metaphysical hypothesis, which resolves all matter into
properties, and refers all things to ideas, leaves the mind in a state of
uncertainty and bewilderment.
Adapting the views of Dumas, with some modifications,[26] it will be found
more satisfactory to regard the ultimate atoms of matter as points beyond
the reach of our examination; which, according to a law, determined by the
influences of the so-called imponderable forces, unite to form molecules.
Again, these molecules combine to form the particles of the mass which we
may regard as the limit of mechanical division. The particles of solid bodies

are solid, those of fluids fluid, and those of gaseous bodies are themselves
aëriform; but it does not follow that the molecules of any body should be
necessarily solid, fluid, or aëriform, from the circumstance of their having
formed the particles of a body in one of these states.
As this planet—a molecule in space—is formed of aggregated atoms, and
enveloped by its own physical agencies—and as it is involved in the
infinitely extending influences of other planetary molecules, and thus forms
part of a system—so the molecules of any mass are grouped into a system
or particle, which possesses the great characteristic features of the whole.
In an aëriform body the particles are in a state of extreme tenuity, the
molecules being themselves, by the influence of some repulsive force, just
on the verge where cohesion exerts its decaying power. In fluid bodies the
attenuation of the particles is less—the particles and also the molecules are
nearer together,—whereas, in the solid body, the forces of cohesion are
most strongly exerted, and all the molecular conditions brought more
powerfully into action.
Under the term molecular force, we include several agencies,—not alike in
the phenomena which they exhibit, but which are all-powerful in producing
the general characteristics of bodies. These require a somewhat close
examination. All the particles of even a solid mass may be brought under
conditions on which they are free to move. By heat we can increase the
length and thickness of a bar of iron, or any other metal, and at length
produce the fluid state,—a melted metal flows as freely as water in a
stream. Fluids, and gases in like manner obey the dispersive influence of
caloric. From these and other analogous results we learn that all bodies have
a greater or less degree of porosity. The distance at which the particles of
fluid bodies are maintained is strikingly proved by the fact, that hydrated
salts dissolved in water occupy no more space than that which is equal to
the water contained in the crystalline body; while anhydrous salts dissolve
without at all increasing the bulk of the fluid. All the solid matter of the salt
must, in these cases, it would appear, go to fill up the interstitial spaces
which we suppose to exist in the liquid.[27]
The conditions which regulate the solubility of bodies, and the power of
solution, regarded either as a mechanical or a chemical process, are very
obscure. We might be led to suppose, that those bodies possessing the

largest amount of unoccupied space were capable of holding the greatest
quantity of soluble matter dissolved. This, however, is far from being the
case, the denser fluids generally having the greatest solvent power.
The peculiar manner in which hydrogen gas appears to dissolve solid
substances,—as iron, potassium, sodium, sulphur, phosphorus, selenium,
and arsenic, may be explained by regarding the results as a manifestation of
the powers of chemical affinity over the forms of bodies. In like manner, the
solution of salt in water, or the mixture of alcohol in that fluid, may be
viewed as chemical phenomena, although usually considered as simple
cases of solution or mixture: alterations of temperature and other physical
changes taking place in either. If two masses of metal,—either tin and
copper, for example,—are melted and combined, the united mass will not
equal the bulk of the two masses. If a pint measure of oil of vitriol and an
equal quantity of water are mixed together, the combined fluids will not fill
a two pint measure.[28]
In these instances a large quantity of heat is rendered sensible, as if it had
been squeezed out by the force with which the particles combined, from
interstices, which were filled with, what we may be allowed to call, an
atmosphere of heat. Hence we conclude that, amongst the influences
determining the molecular constitution of a body, heat performs an
important part. All these facts go to prove that the atoms which form the
compound body, whatever may be its character, are disposed of as so many
centres of force, which act by influences of a peculiar character upon each
other. That these influences are dependent upon known physical forces is
certain; but the laws by which the powers of the ultimate atom are altered
remain still unknown.
In the great operations of nature, changes are produced which we cannot
understand, and variations of condition do certainly occur, which may be
regarded as instances of transmutation.
Amongst others, we may adduce the different states in which we know
carbon to exist. We have the diamond with its beautiful light-refracting
property, its hardness and high specific gravity, capable of being converted
into graphite and coke.[29] Charcoal, graphite, and the diamond, are totally
unlike each other, yet we know they are each composed of the same atoms.
Charcoal is a black irregular substance, light, and readily inflammable;

graphite is crystallizable; but the forms of its crystals cannot be referred to
those of the diamond, and it burns with difficulty. The diamond occurs in
the most regular and beautifully transparent forms; and it can be burned
only at the highest artificial temperatures. We are, however, convinced by
experiment that the brilliant and transparent gem is made up of the same
atoms as those which go to form the dull black mass of charcoal. From
diamonds, as is above stated, coke has been formed by the heat of the
voltaic battery, and recent experiments have proved that the volatilized
carbon constantly passing off from one of the poles of a sufficiently
powerful battery, is deposited in a crystalline powder, possessing most of
the properties, as it regards hardness, &c. of true diamond dust. What is the
mystery of this? We know not. The peculiar conditions have been the
subjects of anxious study; but science has not yet let in a ray of light upon
the mystery. That a different state—it has been called an allotropic
condition—is often induced in the same class of atoms is certain; and hence
the variety of the resulting compounds. To continue our illustrations with
carbon—may not its combinations, in uniform proportions with oxygen and
hydrogen,[30] owe their differences to some allotropic change in the ultimate
atoms of this element.
We know that silicon—the metallic base of flint—is capable of assuming
two or more different states; and that sulphur, selenium, phosphorus, and
arsenic, are susceptible of these remarkable changes in which, without the
slightest variation in the chemical character, a complete change in the
physical condition is produced. Copper, iron, tin, and manganese, are
known to exist in at least two states of physical dissimilarity, and many of
the rarer metals exhibit the same peculiarity.[31] Hence, may we not infer
that some of those substances, which we now term elementary, are but
altered conditions of the same element? The resemblance between many of
those bodies strengthens the supposition. Iridium and platinum,—iron and
nickel,—chlorine, bromine, iodine, and probably fluorine,—are good
examples of these similarities, although these bodies are all distinguished
by physical and chemical differences.
The light-refracting gem, which glistens on the neck of beauty, and is
valued for its transparency, differs only from the rude lump of coke in its
molecular arrangement. Chemistry teaches us that we may, without
producing any disarrangement of the affinities, but by merely setting up

molecular disturbance, effect decided changes, as is strikingly shown in the
colour of iodide of mercury changing from red to yellow under slight
influences of heat, and back again to red by a gentle mechanical
disturbance. By a slight change, merely molecular, iron may be made to
resemble platinum in its physical properties.[32] An iron wire plunged into
nitric acid is attacked by the acid with violence; but if one extremity of the
wire is heated in the flame of a spirit lamp, such a change of state is
produced throughout the entire length of the wire, that if it be now plunged
into nitric acid no effect is produced upon it. On studying this question, we
find good reason for supposing that bodies which, though physically
different, resemble each other in some of their properties, iodine, bromine,
&c., are the results of different allotropic conditions which have been
impressed upon the ultimate atoms, similar to those observed in the
substances named. This hypothesis appears to be more in accordance with
the great principles which we must conceive guided the labours of an
Infinite Mind, than that which supposes a vast number of individual
creations. It will be seen in the sequel that light, heat, electricity, and
chemical action, have the power of producing yet more striking changes in
the forms of bodies. Is it not probable that, according to the operations of
these agents, either combined or separate, acting over different spaces of
time, and under varying circumstances, in relation to the molecular forces,
all those allotropic states may be produced? Hence bodies may be
discovered, which,—from the imperfections of science,—resisting our
means of analysis, must, for a time, be regarded as new elements, whereas
they are possibly only altered states of the same substance.
The experiments of Faraday and of Plücker prove that all matter exists in
certain polar conditions, having powers of mutual attraction and repulsion.
[33]
Are the molecular forces, so called, to be referred to any of those
powers which are involved in the general term magnetic-polarity? Are they
not probably the result of some ultimate principle of which these properties
are but the modified manifestations? These questions will now be generally
answered in favour of magnetism; but in our ignorance we should pause;
the next generation will without doubt find another solution for the
problem.
Franklin supposed the ultimate atoms of bodies to be surrounded by a
subtile fluid or ether, which they have the power of condensing upon their

surfaces with great force—and we have experiments showing that this is
probable[34]—whilst he regarded the atoms of the ether itself as mutually
repellent, thus establishing an equilibrium of forces. Æpinus reduced the
hypothesis of Franklin to a mathematical theory; and Coulomb proved that
the force with which the repulsion of the ethereal atoms and the attraction
of the material molecules are produced, is, like universal attraction,—to
whatever power that may be due,—regulated by the law of the inverse ratio
of the square of the distance. These views are found, upon minute
examination, to hold true to the phenomena with which inductive science
has made us acquainted; and the striking manner in which, when submitted
to the rigorous investigations of geometers, they agree with known
conditions of electricity, appears certainly to favour the opinion that this
power may be materially connected with these molecular arrangements.
Many of the phenomena which are connected with the magnetic influences
also bear in a remarkable manner upon this inquiry. But, without the
necessary proof of direct experimental evidence, it were as unphilosophical
to refer the binding together of the molecules of matter to the agency of
electricity, as it would be to adopt the theory of the hooked atoms of
Epicurus, or the astrological dream of the sympathies of matter.[35]
Science, however, enables us to infer with safety that the mechanical
powers which regulate the constitution of a cube of marble, or a granite
mountain, are of a similar order to those which determine the earth’s
relation to the other planets in the solar system, and that solar system itself a
unit, in the immensity of space, to the myriads of suns which spangle the
stellar vault.
In fine, cohesion, or the attraction of aggregation, is a power employed in
binding particle to particle. To cohesion, we find we have heat opposed as a
repellent force; and the mysterious operations of those electrical
phenomena, generally referred to as polar forces, are constantly, it is
certain, interfering with its powers. In addition, we have seen that in nature
there exists an agency which is capable of changing the constitution of the
ultimate atoms, and of thus giving variety to each resulting mass. What this
power may be, our science cannot tell; but our reason leads us, with firm
conviction, to the belief that it is a principle which is, beyond all others in
its subtile influences which equally universal with, appears to rise superior

to gravitation; and which, like a spirituality, shadows forth to our dwarf
conceptions the immensity of the divine power of the omniscient Creator.
The molecular forces involve a consideration of all the known physical
powers, the study of which, in their operations on matter, will engage our
attention. But it is pleasant to learn, as we advance step by step in our
examination of the phenomena of creation, that we may study the grand in
what externally appears the simple, and learn, in the mysteries of a particle,
the high truths which science has to tell of a planet.
It may appear that the forces of gravitation and cohesion are regarded as
identical. Many phenomena, which we are enabled to reach by the
refinements of inductive inquiry, certainly present to us a striking similarity
in the laws which regulate the operations of these powers; but it must be
remembered that their identity is not established. So far from this, we know
the law of gravitating force. Newton determined with surprising accuracy,
that the action of this power diminishes with the distance as the universe
square, but cohesive force is exerted only at such distances that it is
impossible to determine whether or not it is subjected to the same law. To
quote the words of Young: “The whole of our inquiries respecting the
intimate nature of forces of any kind must be considered merely as
speculative amusements, which are of no further utility than as they make
our views more general, and assist our experimental investigations.”[36]

FOOTNOTES:
[25] “The divisibility of matter is great beyond the power of imagination, but we
have no reason for asserting that it is infinite; for the demonstrations which have
sometimes been adduced in favour of this opinion are obviously applicable to
space only. The infinite divisibility of space seems to be essential to the
conception that we have of its nature, and it may be strictly demonstrated that it
is mathematically possible to draw an infinite number of circles between any
given circle and its tangent, none of which shall touch either of them except at
the general point of contact; and that a ship following always the same oblique
course with respect to the meridian,—for example, sailing north-eastwards,—
would continue perpetually to approach the pole without ever completely
reaching it. But when we inquire into the truth of the old maxim of the schools,
that all matter is infinitely divisible, we are by no means able to decide so
positively. Newton observes that it is doubtful whether any human means may

be sufficient to separate the particles of matter beyond a certain limit; and it is
not impossible that there may be some constitution of atoms, or single
corpuscles, on which their properties, as matter, depend, and which would be
destroyed if the units were further divided; but it appears to be more probable
that there are no such atoms, and even if there are, it is almost certain that matter
is never thus annihilated in the common course of matter.”—The Essential
Properties of Matter: Young’s Natural Philosophy; ed. by Rev. P. Kelland.
[26] “Two very different hypotheses have been formed to explain the nature of
matter, or the mode of its formation; the one known as the atomic theory, the
other, the dynamic. The founder of the former and earlier was Leucippus: he
considered the basis of all bodies to be extremely fine particles, differing in form
and nature, which he supposed to be dispersed through space, and to which his
follower Epicurus first gave the name of atoms. To these atoms he attributed a
rectilinear motion, in consequence of which such as are homogeneous united,
whilst the lighter were dispersed through space. The author of the second
hypothesis was the famous Kant. He imagined all matter existed, or was
originated, by two antagonist and mutually counteracting principles, which he
called attraction and repulsion, all the predicates of which he referred to motion.
Most modern philosophers, and foremost amongst them Ampère and Poisson,
have adopted an hypothesis combining the features of both the preceding. They
regarded the atoms as data, deriving their origin from the Deity as the first cause,
and consider their innate attractive and repulsive force as a necessary condition
to their combination in bodies. The main features of this hypothesis are
borrowed from Aristotle, inasmuch as he supposed the basis of all bodies to be
the four elements known to the ancients, the particles of which, endued with
certain powers, constituted bodies. According to Ampère, all bodies consist of
equal particles, and they again of molecules that, up to a certain distance, attract
each other. Their distance from each other he supposed to be regulated by the
intensity of the attractive and repulsive forces, the latter of which
preponderates.”—Peschel’s Elements of Physics; translated by E. West, 1845.
[27] This was first proved by the researches of Dr. Dalton: the subject will be
again alluded to under the consideration of atomic volumes.
[28] These peculiar phenomena may be studied advantageously in the works of
most of the eminent European chemists. In our own language the reader is
referred to Dr. Thompson’s Outline of the Sciences of Heat and Electricity, 2nd
edition; Brande’s Manual of Chemistry—Art. Specific Heat; Graham’s Elements
of Chemistry; and Daniell’s Introduction to the Study of Chemical Philosophy.
[29] The conversion of the diamond into graphite and coke was first effected by
the agency of the galvanic arc of flame, by M. Jaquelini, and communicated to
the Academy of Sciences in 1847, in a Memoir entitled, De l’action calorifique
de la pile de Bunsen, du chalumeau à gaz oxygène et hydrogène sur le carbon
pur, artificiel et naturel. See Comptes Rendus, 1847, vol. xxiv. p. 1050; also
Report of the British Association, for 1847, (Transactions of Sections) p. 50.
[30] “In the annual report on the progress of chemistry, presented to the Royal
Academy of Stockholm, in March 1840, I have proposed to designate by the
term allotropic state, that dissimilar condition which is observed in certain
elements, and long known examples of which are found in the different forms of
carbon, as graphite and diamond.

“Although these dissimilar conditions, which I have here called allotropic, have
long since attracted attention in one or two elements, still they have been
regarded as exceptions to the general rule. It is at present my object to show that
they are not so rare; that it is probably rather a general property of the elements
to appear in different allotropic conditions; and that although we have hitherto
been unable to obtain several of the elements when uncombined in their
allotropic states, still their compounds indicate the same with tolerable
distinctness.”—Berzelius on the Allotropy of the Elementary Bodies, &c.:
Poggendorff’s Annalen, 1844. Scientific Memoirs, vol. iv. p. 240.
[31] “Copper, when reduced by hydrogen at a heat below that of redness, on
exposure to air soon becomes converted throughout its mass into protoxide; and
when it is triturated for some time with an equivalent quantity of sulphur, it
combines with it according to Böttcher’s experiments, producing flame, and
forming sulphuret of copper. If, however, the copper be reduced by hydrogen at
a red heat, still considerably below the temperature at which it softens and
begins to melt, it remains for years unchanged by exposure to air, and cannot be
made to combine with sulphur without the application of heat. Iron, cobalt, and
nickel, when reduced by hydrogen below a red heat, inflame after they have
cooled, if exposed to the air; and if they are immediately placed in water to
avoid their taking fire, they inflame when they are again removed, and have
become nearly dry. If we compare this behaviour with that of iron reduced by
heat, and with iron in that state in which it forms the conductor of a galvanic
current without becoming oxidized, it would appear that these peculiarities
depended upon something more than a difference of mechanical condition.”—
Berzelius on the Allotropy of Elementary Bodies. See On the Isomeric
Conditions of the Peroxide of Tin: by Prof. H. Rose.—Chemical Gazette, Oct.
1848.
[32] On this curious subject, and its history, see Bergman’s Dissert. de Phlog.
quantitate in Metallis, 1764. Kirwan, On the Attractive Powers of Mineral Acids:
Philosophical Transactions. Kier’s Experiments and Observations on the
Dissolution of Metals in Acids: Phil. Trans. 1790.
From these valuable papers it will be seen that the peculiar states of iron had
already attracted attention, particularly those “inactive conditions” noticed in a
“Note sur la Manière d’agir de l’Acide nitrique sur le Fer, par J. F. W.
Herschel,” Aug. 1833; and previously indicated by M. H. Braconnot, Sur
quelques Propriétés de l’Acide nitrique, Annales de Chimie, vol. lii. p. 54.
Reference should also be made to the Memoirs of Sir John Herschel, On the
Action of the Rays of the Solar Spectrum on Vegetable Colours, &c.: Phil. Trans.
vol. cxxxiii. p. 221; and On the Separation of Iron from other Metals: Phil.
Trans. vol. cxi. p. 293; and several papers by Schönbein, in the Philosophical
Magazine, from 1837.
[33] Faraday, in his memoir On new Magnetic Actions, and on the Magnetic
Conditions of all Matter, says:—“By the exertion of this new condition of force,
the body moved may pass either along the magnetic lines or across them, and it
may move along or across them in either or any direction, so that two portions of
matter, simultaneously subject to this power, may be made to approach each
other as if they were mutually attracted, or recede as if mutually repelled. All the
phenomena resolve themselves into this, that a portion of such matter, when
under magnetic action, tends to move from stronger to weaker places or points

of force. When the substance is surrounded by lines of magnetic force of equal
power on all sides, it does not tend to move, and is then in marked
contradistinction with a linear current of electricity under the same
circumstances.”—Phil. Trans. for 1846, vol. cxxxvii.
[34] New Experiments and Observations on Electricity made at Philadelphia, in
America.—Addressed to Mr. Collinson, from 1747 to 1754. By Benjamin
Franklin. Of these Priestley remarks:—“It is not easy to say whether we are most
pleased with the simplicity and perspicuity with which the author proposes every
hypothesis of his own, or the noble frankness with which he relates his mistakes,
when they were corrected by subsequent experiments.”
[35] “The atomic philosophy of Epicurus, in its mere physical contemplation,
allows of nothing but matter and space, which are equally infinite and
unbounded, which have equally existed from all eternity, and from different
combinations of which every visible form is created. These elementary
principles have no common property with each other; for whatever matter is, that
space is the reverse of; and whatever space is, matter is the contrary to. The
actual solid part of all bodies, therefore, are matter, their actual pores space, and
the parts which are not altogether solid, but an intermixture of solidity and pore,
are space and matter combined.
“The infinite groups of atoms, flying through all time and space in different
directions and under different laws, have interchangeably tried and exhibited
every possible mode of rencounter: sometimes repelled from each other by
concussion, and sometimes adhering to each other from their own jagged or
pointed construction, or from the casual interstices which two or more connected
atoms must produce, and which may be just adapted to those of other figures,—
as globular, oval, or square. Hence the origin of compound and visible bodies;
hence the origin of large masses of matter; hence, eventually, the origin of the
world itself.”—Dr. Good’s Book of Nature.
[36] Young’s Lectures on Natural Philosophy and the Mechanical Arts. Lecture
49, On the Essential Properties of Matter.

CHAPTER V.
CRYSTALLOGENIC FORCES.
Crystallisation and Molecular Force distinguished—Experimental
Proof—Polarity of Particles forming a Crystal—Difference
between Organic and Inorganic Forms—Decomposition of
Crystals in Nature—Substitution of Particles in Crystals—
Pseudomorphism—Crystalline Form not dependent on
Chemical Nature—Isomorphism—Dimorphism—Theories
of Crystallogenic Attraction—Influence of Electricity and
Magnetism—Phenomena during Crystallisation—Can a
change of Form take place in Primitive Atoms?—Illustrative
Example of Crystallisation.

“Crystallisation is a peculiar and most admirable work of nature’s geometry,
worthy of being studied by all the power of genius, and the whole energy of
the mind, not on account of the delight which always attends the knowledge
of wonders, but because of its vast importance in revealing to us the secrets
of nature; for here she does, as it were, betray herself, and, laying aside all
disguise, permits us to behold, not merely the results of her operations, but
the very processes themselves.”—Such is the language of an Italian
philosopher, Gulielmini; and it is the striking peculiarity of beholding the
process of the formation of the regular geometric figures of crystals, the
gradual accretion of particle to particle, which induces us to separate
crystallization from mere molecular aggregation. Without doubt the
formation of a crystal and the production of an amorphous block are due to
powers which bear a close resemblance in many points; but they present
remarkable differences in others.
Let us take some simple case in illustration. In quiet water we have very
finely divided matter suspended, and matter in a state of solution. The first
is slowly precipitated, and in process of time consolidates into a hard mass
at the bottom, presenting no particular character, unless it has been placed
in some peculiar physical conditions; when, as in nature, we have a regular

bedding which is intersected by lines of lamination or of cleavage, which
we are, from experiment, enabled to refer to the influence of current
electricity. The second—the matter in solution—is also slowly deposited;
but it is accumulated upon nuclei which possess some peculiar disposing
powers, and every particle is united by some particular face, and an angular
figure of the most perfect character results. Many pleasing experiments
would appear to show that electricity has much to do in the process of
crystallization; but it is evident that it must be under some peculiarly
modified conditions that this power is exerted, if, indeed, it has any direct
action.
The same substances always crystallize in the same forms, unless the
conditions of the crystallizing body are altered. It has been supposed that
each particle of a crystalline mass has certain points or poles which possess
definite properties, and that cohesion takes place only along lines which
have some relation to the attracting or repelling powers of these poles. We
shall have, eventually, to consider results which appear to prove that
magnetism is universal in its influence, and that this polarity of the particles
of matter may be referred to it.
Be the cause of crystallisation what it may, it presents to us in appearance a
near approach in inorganic nature to some of the peculiar conditions of
growth in the organised creation. In one, we have the gradual production of
parts and the formation of members due to peculiar powers of assimilation,
each individual preserving all its distinguishing features; and in the other,
we have a regular order of cohesion occurring under the influence of a
power which draws like to like, and arranges the whole into a form of
beauty.
This appears to be the proper place for correcting an error too prevalent,
relative to the formation of crystals, the development of cells, and the yet
more fatal falsehood of referring the great phenomena of Life to any of the
physical forces with which we are acquainted.
The Crystal forms, by the accretion of particle to particle, along lines
determined by some yet unknown power. There is no change in the
character of any particle—like coheres to like; the first atom and the last of
the series being identical in character.

The Plant grows, not by the gathering together of similar particles of
matter, but by the absorption of a compound particle—by that one which
must be regarded as the primary nuclear atom or cell. After this absorption
—in virtue of a power which we call life, excited into action by light—the
compound particle is decomposed, and one constituent is retained to effect
the formation of a new cell, whilst the other is liberated as an invisible air.
Here we have a change of chemical constitution effected; and this takes
place through the whole period of vegetable growth, from the development
of the plumule up to the formation of the latest leaf upon the topmost
branch of the most lordly tree.
Life has been referred to electricity and to chemical power—as the effect of
a known cause. Without doubt, during the operations of life the whole of the
physical powers are necessary to the production of all the phenomena of
growth in the vegetable and the animal world. But these powers are ever
subsidiary to vital force, and are like attendant spirits chained to do an
enchanter’s bidding.
Life is a force beyond the reach of human search, and he who fancies he has
a hold upon the principle which produced biological phenomena, has
committed himself to as wild a pursuit as he who rashly endeavours to catch
a morass-meteor.
Subtile as are the forces of light, heat, and electricity—that of life, vitality,
is infinitely more refined, and it must for ever elude the search of the
philosopher.
Man is permitted to test and try all things which are created, and to apply to
useful ends the discoveries which he may make. But man can never become
a creator; and he who would attempt to give sense to an inert mass of
matter, by electricity, heat, or light, will prove himself as ignorant of
nature’s truth as is the senseless mass upon which he works.
“So far shalt thou go, and no further,” was said equally to the great tide-
wave of human intellect, as to the mighty surge of the earth-girdling ocean.
It must not be forgotten that a striking difference exists between the
productions of the mineral and the other kingdoms of nature. Animals and
vegetables arrive at maturity by successive developments, and increase by
the assimilation of substances, having the power of producing the most

important chemical changes upon such matter as comes within the range of
their influence; but minerals are equally perfect in the earliest stages of their
formation, and increase only, as previously said, by the accretion of
particles without their undergoing any change.
The animal and vegetable tribes cease to continue the functions of life:
death ensues, and a complete disorganisation takes place; but this is not the
case in the mineral world: the crystal being the result of a constantly acting
force is not necessarily liable to decomposition.
Nevertheless, we sometimes find in nature that crystals, after arriving at
what may be regarded as, in some sort, their maturity, are, owing to a
change of the conditions under which they were formed, gradually
decomposed. In our mines we discover skeletons of crystals, and within the
hollow shell thus formed, other crystals of a different constitution and
figure find nuclei, and the conditions required for their development. Again,
to give a striking instance, the felspar crystals of the granitic formations are
liable to decomposition in a somewhat peculiar manner. In decomposing,
these crystals leave moulds of their own peculiar forms, and it not
unfrequently happens, in the stanniferous districts of Cornwall, that oxide
of tin gradually fills these moulds, and we procure this metallic mineral in
the form of the earthy one. Then we have the curious instances of bodies
crystallising in a false form under change of circumstances. We find, for
example, Pseudomorphism, (or false-form), as this class of phenomena is
named, occurring by the removal of the constituent atoms of one crystal,
while another set—which naturally assumes a different form—takes their
place, yet still preserving the original shape. It often happens that copper
pyrites will, in this manner, exhibit the angles of an ordinary variety of
crystallised carbonate of iron. These curious changes may be familiarised
by supposing a beautiful statue of gold, from which some skilful mechanic
removes particle by particle, and so skilfully substitutes a grain of brass for
every one of gold removed, that the loss of the precious metal cannot be
detected by any mere examination of its form.
Crystalline form is not strictly dependent upon the chemical nature of the
parts forming the crystal. The same number of atoms, arranged in the same
way, produce the same form. Substances much unlike each other will
assume the same crystalline arrangement. Magnesia, lime, oxide of
cadmium, the protoxides of iron, nickel, and cobalt, combined with the

same acid, present similarly formed bodies. These Isomorphic (like-form)
[37]
peculiarities are exceedingly common, and the discoverer of the
phenomena, Mitscherlich, announced the above law. It cannot, however, be
regarded as a philosophical expression of the fact, and requires
reconsideration—chemical elements of a dissimilar character may have the
same law of aggregation, and thus produce the same form, without having
any relation to the number of atoms.
We also find compounds which have two distinct systems of crystallisation.
This property, Dimorphism, is very strikingly shown in carbonate of lime,
which occurs in rhombohedrons, in calc spar, and in rhombic prisms in
arragonite. The molecular arrangements here are not, however, of equal
stability, and one form is evidently forced upon the other, and is abandoned
by it on the slightest disturbance. When a prism of arragonite is heated it
breaks up into the rhombs of common calc spar, at a temperature far below
that at which the carbonate of lime is decomposed; but no alteration of
temperature can convert calc spar into arragonite.
Crystals are found in the most microscopic character, and of an exceedingly
large size. A crystal of quartz at Milan is three feet and a quarter long, and
five feet and a half in circumference, and its weight is 870 pounds. Beryls
have been found in New Hampshire measuring four feet in length.[38]
In the dark recesses of the earth, where the influences which produce
organisation and life cease to act, a creative spirit still pursues its never-
ending task of giving form to matter.
The science of crystallogeny,[39] embracing the theoretical and practical
question of the causes producing these geometric forms, has in various
ways attempted to explain the laws according to which molecules arrange
themselves on molecules in perfect order, giving rise to a rigidly correct
system of architecture. But it cannot be said that any theory yet propounded
is sufficiently exact to embrace the whole of the known phenomena, and the
questions,—What is crystallogenic attraction, and what is the physical
nature of the ultimate particles of matter,—are still open for the inquiries of
that genius which delights in wrestling with the secrets of nature.
The great Epicurus speculated on the “plastic nature” of atoms, and
attributed to this nature the power they possess of arranging themselves into

symmetric forms. Modern philosophers satisfy themselves with attraction,
and, reasoning from analogy, imagine that each atom has a polar system.
Electricity, and light, and heat, exert remarkable powers, and accelerate or
retard crystallisation according to the conditions under which these forces
are brought to bear on the crystallising mass. We have recently obtained
evidence which appears to prove that some form of magnetism has an
active influence in determining the natural forms of crystals, and we
discover that magnetism exerts a peculiar influence in relation to the optic
axes of crystals, which is not exerted in lines at right angles to these.
Electricity appears to quicken the process of crystalline aggregation—to
collect more readily together those atoms which seek to combine—to bring
them all within the limits of that influence by which their symmetrical
forms are determined; and strong evidence is now afforded, in support of
the theory of magnetic polarity, by the refined investigations of Faraday and
Plücker, which prove that magnetism has a directing influence upon
crystalline bodies.[40]
It has been found that crystals of sulphate of iron, slowly forming from a
solution which has been placed within the range of sufficiently powerful
magnetic force, dispose themselves along certain magnetic curves, such as
are formed around a magnet by steel filings; whereas the crystals of the
Arbor Dianæ, or silver tree, forming under the same circumstances, take a
position nearly at right angles to these curves. Certain groups of crystals
have been found in nature, which appear to show, by their positions, that
terrestrial magnetism has been active in producing the phenomena they
exhibit; indeed, nearly all our mineral formations indicate the influences of
this, or some similarly acting power.[41]
During rapid crystallisation, some salts—as the sulphate of soda, boracic
acid, and arsenious acid crystallising in muriatic acid—exhibit decided
indications of electrical excitement; light is given out in flashes. We have
evidence that crystals exhibit a tendency to move towards the light, and that
crystallisation takes place more readily, and progresses with greater activity
in the sunshine than in the shade. Professor Plücker has recently ascertained
that certain crystals—in particular the cyanite—“point very well to the
north, by the magnetic power of the earth only. It is a true compass needle;
and, more than that, you may obtain its declination.” We must remember
that this crystal, the cyanite, is a compound of silica and alumina only. This

is the amount of experimental evidence which science has afforded in
explanation of the conditions under which nature pursues her wondrous
work of crystal formation. We see just sufficient of the operation to be
convinced that the luminous star which shines in the brightness of Heaven,
and the cavern-secreted gem, are equally the result of forces which are
known to us in only a few of their modifications.
Every substance, when placed under circumstances which allow of the free
movement of its molecules, has a tendency to crystallise. All the metals
may, by slowly cooling from the melting state, be exhibited with a
crystalline structure. Of the metallic and earthy minerals, nature furnishes
us with an almost infinite variety of crystals, and, by a reduction of
temperature, yet more simple bodies assume the most symmetric forms.
Water, in the conditions of ice and snow, is a familiar and beautiful
example; and, by such extreme degrees of cold as are artificially produced,
many of the gases exhibit a tendency to a crystalline condition.
May not the solid elementary atoms be susceptible of change of form under
different influences? May not the different states under which the same
bodies are found—as, for example, silica, carbon, and iron—be due entirely
to a change in the form of the primitive atom?
Admitting the probability of this, we then easily see that the central
molecule, formed of an aggregation of such atoms, uniting by particular
faces, would present a determinate form; and that the resulting crystal, a
mass of such molecules, cohering according to a given law, at certain
angles, would present such geometric figures as we find in nature, or
produce in our laboratories, when we avail ourselves of processes which
nature has taught us.
If we take a particle of marble, and place it in a large quantity of water
acidulated with sulphuric acid, it dissolves, and a new compound results.
The marble disappears—the eye cannot detect it by form or colour: the acid
also has been disguised—the taste discovers nothing sour in the fluid. We
have, in combination with the water, the lime and sulphuric acid; but that
combination appears to the eye in no respect different from the water itself.
It is colourless and perfectly transparent, although it holds a mass of solid
matter which previously would not allow of the permeation of a ray of light.
Let us expose this fluid to such circumstances that the water will slowly

evaporate, and we shall find forming in it, after a time, microscopic
particles of solid, light-refracting matter. These particles gradually increase
in size, and we may watch their growth until eventually we have a
symmetric figure, beautifully shaped, the primary form of which is a right
rhomboidal prism. Thus in nature, by the action, in all probability, of
vegetable matter on the sulphates held in solution by the water of the great
rivers and the ocean—aided by our oxidizing atmosphere—sulphuric acid is
produced to do its work upon the limestone formations, and from this
combination would result the well-known gypsum, or plaster of Paris,
which ordinarily exists as an amorphous mass, but is often found in a
crystalline form.[42]
This is a very perfect illustration of the wonderful process we have been
considering, and in which, simple though it appears to be, we have set to
work a large proportion of the known physical elements of the universe. By
studying aright the result which we have it in our power to obtain in a
watch-glass, we may advance our knowledge of gigantic phenomena, which
are now progressing at the bottom of the ocean, or of the wondrous
agencies which are in operation, producing light-refracting gems within the
secret recesses of the rocky crust of our globe.
The force of crystallisation is a subject worthy of much consideration. If we
examine our slate rocks, through which little veins filled with quartz
crystals are spread, we shall see that the mechanical force exerted during
the production of these crystals has been capable of rending those rocks in
every direction. Those fissures formed by the first system of crystalline
veins, in order of time, are filled in by another set of crystalline bodies,
which equally exert their mechanical power, and thus produce those curious
intersections and dislocations which were long a puzzle to the geologist.
The simplest power, slowly and constantly acting through a long period of
time, may become sufficient, eventually, to rend the Andes from base to
summit, or to lift a new continent above the waters of the ocean.

FOOTNOTES:

[37] “Gay Lussac first made the remark, that a crystal of potash alum,
transferred to a solution of ammonia alum, continued to increase without its
form being modified, and might thus be covered with alternate layers of the two
alums, preserving its regularity and proper crystalline figure. M. Beudant
afterwards observed that other bodies, such as the sulphates of iron and copper,
might present themselves in crystals of the same form and angles, although the
form was not a simple one, like that of alum. But M. Mitscherlich first
recognised this correspondence in a sufficient number of cases to prove that it
was a general consequence of similarity of composition in different bodies.”—
Graham’s Elements of Chemistry (1842), p. 136.
The following remarks are from a paper by Dr. Hermann Kopp, On the Atomic
Volume and Crystalline Condition of Bodies, &c., published in the Philosophical
Magazine for 1841:—“The doctrine of isomorphism shows us that there are
many bodies which possess an analogous constitution, and the same crystalline
form. Our idea of the volume (or, in other words, of the crystalline form) of
these bodies must therefore be the same. From this it follows that their specific
weight is connected with mass contained in the same volume. From these
considerations the following law may be deduced: The specific weight of
isomorphous bodies is proportional to their atomic weight, or isomorphous
bodies possess the same atomic volume.”—page 255. A translation appears in
the Cavendish Society, from Dr. Otto’s Chemistry, On Isomorphism, which may
be advantageously consulted. See also a paper by M. Rose, translated from the
Proceedings of the Royal Berlin Academy for the Chemical Gazette, Oct. 1848,
entitled, On the Isomeric Conditions of the Peroxide of Tin.
[38] A System of Mineralogy, comprising the most recent discoveries, by James
D. Dana, A.M., New York, 1844.
[39] Crystallogeny, or the formation of crystals, is the term employed by Dana,
in his admirable work quoted above: whose remarks on Theoretical
Crystallogeny, p. 71, are well worthy of all attention.
[40] On the Magnetic Relations of the Positive and Negative Optic Axes of
Crystals, by Professor Plücker, of Bonn.—Philosophical Magazine, No. 231 (3rd
Series), p. 450. Experimental Researches on Electricity; On the Crystalline
Polarity of Bismuth and other bodies, and on its Relation to the Magnetic form
of Force: by Michael Faraday, Esq., F.R.S.—Transactions of the Royal Society
for 1848.
[41] In the Memoirs of the Geological Survey of the United Kingdom, and of the
Museum of Economic Geology, vol. i. 1846, will be found a paper, by the author
of this volume, On the Influences of Magnetism on Crystallisation, and other
Conditions of Matter, in which the subject is examined with much care. See also
Magnétisme polaire d’une montagne de Chlorite schisteuse et de Serpentine:
Annales de Chimie, vol. xxv. p. 327; Influence du Magnétisme sur les actions
chimiques, by l’Abbé Rendus; and also a notice of the experiments of Ritter and
Hansteen, “Analysées par M. Œrsted;” also Effets du Magnétisme terrestre sur la
précipitation de l’Argent, observés par M. Muschman: Annales de Chimie, vol.
xxxviii. p. 196–201.
[42] The transparent varieties of sulphate of lime are distinguished by the name
Selenite; and the fine massive varieties are called Alabaster. Gypsum forms very
extensive beds in secondary countries, and is found in tertiary deposits;

occasionally, in primitive rocks; it is also a product of volcanoes. The finest
foreign specimens are found in the salt mines of Bex, in Switzerland; at Hall, in
the Tyrol; in the sulphur-mines of Sicily; and in the gypsum formation near
Ocana, in Spain. In England, the clay of Shotover Hill, near Oxford, yields the
largest crystals.—See Dana’s Mineralogy, second edition, p. 241.

CHAPTER VI.
HEAT—SOLAR AND TERRESTRIAL.
Solar and Terrestrial Heat—Position of the Earth in the Solar
System—Heat and Light associated in the Sunbeam—
Transparency of Bodies to Heat—Heating Powers of the
Coloured Rays of the Spectrum—Undulatory Theory—
Conducting Property of the Earth’s Crust—Convection—
Radiation—Action of the Atmosphere on Heat Rays—
Peculiar Heat Rays—Absorption and Radiation of Heat by
dissimilar Bodies—Changes in the Constitution of Solar
Beam—Differences between Transmitted and Reflected
Solar Heat—Phenomena of Dew—Action of Solar Heat on
the Ocean—Circulation of Heat by the Atmosphere and the
Ocean—Heat of the Earth—Mean Temperature—Central
Heat—Constant Radiation of Heat Rays from all Bodies—
Thermography—Action of Heat on Molecular Arrangements
—Sources of Terrestrial Heat—Latent Heat of Bodies—
Animal Heat—Eremacausis—Spheroidal State Cold—
Condensation—Freezing—Theories of Heat—Natural
Phenomena—and Philosophical Conclusion.

We receive heat from the sun, associated with light; and we have the power
of developing this important principle by physical, mechanical, and
chemical excitation, from every kind of matter. Our convictions are, that the
calorific element, whether derived from a solar or a terrestrial source,
presents no essential difference in its physical characters; but as there are
some remarkable peculiarities in the phenomena, as they arise from either
one or the other source, it will assist our comprehension of this great
principle, if we consider it under the two heads.
Untutored man finds health and gladness in the warmth and light of the sun;
he rears a rugged altar, and bows his soul in prayer, to the principle of fire,
which in his ignorance he regards as the giver and the supporter of life. The

philosopher finds life and organization dependent upon the powers
combined in the sunbeam; and, examining the phenomena of this wonderful
band of forces, he is compelled to acknowledge that the flame upon the
altar—on the Persian hills,—was indeed a dim shadow of the infinite
wisdom which abides behind the veil.
The present condition of our earth is directly dependent upon the amount of
heat we receive from the sun. It has frequently been said, that if it were
possible to move this planet so much nearer that orb that the quantity of
heat would be increased, the circumstances of life would necessarily be so
far changed, that all the present races of animals must perish; and that the
same result would happen from any alteration which threw us yet further
from our central luminary, when, owing to the extremity of cold and the
wretchedness of gloom, all living creatures would equally fail to support
their organization.
To move the earth nearer to, or more distant from the sun, is an
impossibility; but it has been argued that those planets which are near to the
sun must possess a temperature which would melt our solid rocks, and
vaporize the ocean,—while Uranus and Neptune must, from their distance
from the source of heat, have so small an amount, that water must become
solid as the rock, and such an atmosphere as that of the earth exist as a
dense liquid.
It will be shown that according to the physical condition of the material
substances, so are their powers regulated of absorbing and retaining the heat
which falls as a radiant power upon their surfaces. Heat rays, in passing
through the attenuated medium of planetary space, lose none of their power
—this we know from the fact that even the less dense upper region of the
earth’s atmosphere takes from the solar rays but an exceedingly small
quantity of heat. Therefore, whether a solar heat ray traverses through one
million, or one hundred million miles of space, it still retains its power
equally of imparting warmth to the solid matter by which it is intercepted.
There is no law of variation as the inverse square of the distance of those
radiating powers. Consequently, there is no reason why the physical
conditions, alike of the nearest and the most remote planetary bodies,
should not be so adjusted that they all enjoy that life promoting temperature
which belongs to the earth.

All the objects around us are adapted to the circumstances of the earth’s
position in relation to the sun, to which we are bound by the principle of
gravitation; opposed to that centrifugal force which tends constantly to
drive the moving planetary mass off from the centre of power. The balance
maintains its perfect equilibrium, although we have one power constantly
drawing the earth towards the sun, and the other as constantly exerting itself
to move it off into space at a tangent to the orbit in which the planet moves.
In our examination it will be found that one common system of harmony
runs through all the cosmical phenomena, by which everything is produced
that is so beautiful and joyous in this world.
Heat, and the other elementary radiant principles, are often combined as the
common cause of effects evident to our senses. The warmth of the solar
rays, and their luminous influence, are not, however, commonly associated
in the mind as the results of a single cause. It is only when we come to
examine the physical phenomena connected with these radiations that we
discover the complexity of the inquiry. Yet it is out of these very subtle
researches that we draw the most refined truths. The high inferences to
which the analysis of the subtile agencies of creation leads us, render
science, pursued in the spirit of truth, a great system of religious instruction.
Although we do not fear that heat and light can be confounded in the mind,
so different are their phenomena,—we have heat rays, as from dark hot
iron, which give no light, while in the full flood of the lunar rays the heat is
scarcely appreciable by the most delicate instruments;—yet it is important
to show how far these two principles have—been separated from each
other. Transparent bodies have varied powers of calorific transparency, or
transcalescence: some obstructing the heat radiated from bodies of the
highest temperatures almost entirely even in the thinnest layers; whilst
others will allow the warmth of the hand to pass through a thickness of
several inches. Liquid chloride of sulphur, which is of a deep red colour,
will allow 63 out of 100 rays of heat to pass, and a solution of carmine in
ammonia, or glass stained with oxides of gold, or copper, rather a greater
number; yet these transparent media obstruct a large quantity of light.
Colourless media obstructing scarcely any light, will, on the contrary,
prevent the passage of calorific rays. Out of every hundred rays, oil of
turpentine will only transmit 31, sulphuric ether 21, sulphuric acid 17, and
distilled water only 11. Pure flint glass, however, is permeated by 67 per

cent. of the thermic rays, and crown glass by 49 per cent. The body
possessing the most perfect transparency to the rays of heat is diaphanous
salt-rock, which transmits 92, while alum, equally translucent, admits the
passage of only 12 per cent.[43]
Black mica, obsidian, and black glass, are nearly opaque to light, but they
allow 90 per cent. of radiant heat to pass through them; whereas a pale
green glass, coloured by oxide of copper,[44] covered with a layer of water,
or a very thin plate of alum, will, although perfectly transparent to light,
almost entirely obstruct the permeation of heat rays.
We thus arrive at the fact that heat and light may be separated from each
other; and if we examine the solar beam by that analysis which the prism
affords, we shall find that there is no correspondence between intense light
and ardent heat. By careful observation, it has been proved, when we have a
temperature of 62° F. in the yellow ray, which ray has the greatest
illuminating power; that below the red ray, out of the point of visible light,
the temperature is found to be 79°, while at the other end of the spectrum, in
the blue ray, it is 56°, and at the end of the violet ray no thermic action can
be detected.[45]
From the circumstance, that as we, by artificial means, raise the temperature
of any body, and produce intense heat, so after a certain point of thermic
elevation has been obtained, we occasion a manifestation of light.[46] It has
been concluded, somewhat hastily, that heat and light differ from each other
only in the rapidity of the undulations of an hypothetical ether.
It must be admitted that the mathematical demonstrations of many of the
phenomena of calorific and luminous power are sufficiently striking to
convince us that a wave-movement is common to both heat and light. The
undulatory theory, however, requires the admission of so many premises of
which we have no proof; its postulates are, indeed, in many cases so
gratuitous, that notwithstanding the array of talent which stands forward in
its support, we must not allow ourselves to be deceived by the deductions of
its advocates, or dazzled by the brilliancy of their displays of learning.
Radiant heat appears to move in waves; but that calorific effects in material
bodies are established by any system of undulation, is a deduction without a

proof; and the thermic phenomena of matter are as easily explained by the
hypothesis of a diffusive subtile fluid.
We have not, however, to prove the correctness of either of the opposing
views; indeed, it is acknowledged that many phenomena require for their
explanation conditions which are not indicated by either theory.
The earth receives its heat from the sun; a portion of it is conducted from
particle to particle into the interior of the rocky crust. Another portion
produces warmth in the atmosphere around us, by convection, or the
circulation of particles; those warmed by contact with the surface becoming
lighter, and ascending to give place to the colder and heavier ones. A third
portion is radiated off into space, according to laws which have not been
sufficiently investigated, but which are dependent upon the colour, chemical
composition, and mechanical structure of the surface.
It cannot but be instructive to contemplate the indications which we have of
the dependence of all that is beautiful on earth, on the heat and light
radiations which we receive from the sun. Let us endeavour to realise some
of the effects which arise from even the temporary deprivation of solar heat.
It is winter, the vegetable world appears chilled to its centre. The trees,
except a few of the hardy evergreens, are bare of leaves, and stretching
forth their branches into the cold air, they realise the condition of vegetable
skeletons. The lowly plants of the hedge-row, and the grasses of the field,
show that their vital power is subdued to that minimum degree of action
which is but a few slight removes from death. The life of the running stream
is suspended, it is cased in the “thick-ribbed ice,” and the waters beneath no
longer send forth their joyous music to the genial breeze. Even within the
temperate limits of our own land, the aspect of winter convinces the
ordinary observer, that the loss of heat has been followed by diminished
activity in the powers of life; and the philosopher discovers that the
lessened energies of solar light, and the weaker action of the radiant heat,
have aided in producing that repose which is a little more than sleep—a
little less than death.
It is night, and winter: the earth is parting with its heat,—with the absence
of light, there is a still greater loss of vigour, a yet further diminution of the
powers of life. Even the animal races, sustained by vital influences of a
more exalted kind, sink under the temporary deprivation of the solar rays to

a monotonous, a melancholy repose. All animals undergo different degrees
of hybernation, and each in his winter retreat supports vitality by preying
upon himself. The world is hung in mourning black; there is no play of
colours to harmonize the human spirit by sending their ethereal pulsations
to the human eye, and it is only the consciousness that when the night is at
the darkest, the day is nearest, that even man’s soul is sustained against the
depressing influences of the absence of the sun.
The conditions which we must observe at our own doors cannot fail to
convey as a conviction to the least imaginative mind, that a slightly
prolonged continuance of darkness, with its consequent increase of
coldness, would be fatal to the existence of the organic world.
The sun has entered Aries: it is spring. The length of the day and night are
equal, the powers of light and darkness are now exactly balanced against
each other, and light, like the Archangel, triumphs over the sombre spirit.
The organic world awakes. Chemical action commences in the seed, the
vital spark is kindled in the embryo, and under the impulsive force of some
solar radiations the plant struggles into light and life. The same invigorating
force impels the circulation of the sap through the capillary tubes of the
forest tree, until the topmost branch trembles with the new flow of life. The
buds burst forth into leaf, and a fresh and lively covering spreads over those
branches which, in their nakedness, could scarcely be distinguished from
the dead.
The animal races are no less sensible of the new influence which is diffused
around. The birds float joyously upon the breeze, and give to heaven their
trilling songs of praise. The beasts come forth from the clefts of the rocks
and the tangled shelters of the forests, and gambol in the full luxury of their
renewed vigour. Man, even man, the inhabitant of cities, trained and
tempered to an artificial state, awakes of a spring morning with a fuller
consciousness of mind, and a deeper and more pleased sense of his
intelligence, than when the fogs and gloom of winter hung like the charmed
robe upon the limbs of the giant. Now, the dormant poetry of man seeks
expression. As the morning sun is said to have awakened the musical
undulations of the Memnonian statue, so the sun of the vernal morning
produces in the mind of the most earthly, faint pulsations of that heaven-
born music, which neither sin nor sorrow can entirely destroy. The
psychologist, in studying the peculiar phenomena of the human mind, must

associate himself with the natural philosopher, and learn to appreciate the
influence of physical causes in determining effects which our elder
philosophers and the poets of every age have attributed to spiritual
agencies.
Summer, with its increased heat and light, reigns over the land. The work of
life is now at its maximum, and every energy is quickened throughout the
organic creation. The laws of nature are arranged on the principle of
antagonistic forces, the constant struggle to maintain them in equilibrium
constituting the sensible phenomena of existence. Heat and light, with
chemical power and electricity, have been quickening the unknown
principle of life, until it has become exhausted in the production of new
parts—in the strange phenomenon of growth—the formation of organized
matter from the inorganic stores of creation.
The autumn, with its tempered sunlight, comes, but in the solar radiance we
discover new powers, and under the influence of these the flower and the
fruit have birth. The store of a new life is centered in the seed, and though
the leaf falls, and the flower fades, a new set of organisms are produced, by
which the continuance of the species is secured.
Let any man examine himself as the seasons change, and he will soon be
convinced that every alternation of light and darkness, of heat and its
absence, produces new sets of influences equally on the mind and on the
body, showing the entire dependence of the animal and vegetable kingdoms
upon those causes which appear to flow from the centre of our planetary
system.
The phenomena which connect themselves with the changes of the seasons
cannot fail to convince the most superficial thinker that there is an intimate
connection between the sun and the earth which deserves our close
attention.
Indeed, if we examine the most ancient of histories, we find one great fact
at the base of all their philosophies. Moses connects darkness with a void
and formless earth, and light with the creation of harmony and life. Menis
sings of a fearful world by “many formed darkness encircled,” and links the
idea of a “life-breathing divinity” with the awakening of light upon created
things. The Egyptian Isis, the Grecian Apollo, who,

The Lord of boundless light
Ascending calm o’er the empyrean sails,
And with ten-thousand beams his awful beauty veils,

the fire-worshipper of the Persian hills and the sun-god of the Peruvian
mountains, exhibit, through time and space, the full consciousness of man
to the influences of solar light and heat upon the organic creations of which
he is himself the chief exemplar.
The investigations of modern philosophers have extended these influences
to the inorganic masses which constitute the Planet Earth:—and we now
know that the physical forces, ever active in determining the chemical
condition and the electrical relations of matter, are directly influenced by
the solar radiations.
Few things within the range of our inquiry are more striking than the
phenomena of calorific radiation and absorption. They display so perfectly
the most refined system of order, and exhibit so strikingly the admirable
adaptation of every formation to its particular conditions, and for its part in
the great economy of being, that they claim most strongly the study of all
who would seek to discover a poetry in the inferences of science.
Owing to the nature of our atmosphere, we are protected from the influence
of the full flood of solar heat. The absorption of caloric by the air has been
calculated at about one-fifth of the whole in passing through a column of
6,000 feet. This estimate is, of course, made near the earth’s surface; but we
are enabled, knowing the increasing rarity of the upper regions of our
gaseous envelope in which the absorption is constantly diminishing, to
prove, that about one-third of the solar heat is lost by vertical transmission
through the whole extent of our atmosphere.[47]
Experience has proved that the conditions of the sun’s rays are not always
the same; and there are few persons who have not observed that a more than
usual scorching influence prevails under some atmospheric circumstances.
This is also evidenced in the effects produced on the foliage of trees, which,
though often attributed to electricity, is evidently due to heat. An
examination of the solar radiations, as exhibited in the prismatic spectrum,
has proved the existence of a class of heat rays, which manifest themselves

by a very peculiar deoxidizing power quite independent of their caloric
properties, to which the name of parathermic rays has been given.[48] We
are protected from the severe effects of these rays by the ordinary state of
the medium through which the solar heat passes. Our atmosphere is a
mixture of gases and aqueous vapour; and it has been found, as already
stated, that even a thin film of water, however transparent, prevents the
passage of many calorific radiations, and the rays retarded are, for the most
part, of that class which have this peculiar scorching power. The air is, in
this way, the great equaliser of the solar heat, rendering the earth agreeable
to all animals, who, but for this peculiar absorbent medium, would have to
endure, even in our temperate clime, the burning rays of a more than
African sun.
The surface of the earth during the sunshine—and, though in a less degree,
even when the sun is obscured by clouds—is constantly receiving heat; but
the rate of its absorption varies. Benjamin Franklin showed, by a set of
simple but most conclusive experiments, that a piece of black cloth was
warmed much sooner than cloth of a lighter colour;[49] and we know, from
observations of a similar class, that the bare brown soil receives heat more
readily than the bright green grassy carpet of the earth. Consequently,
during the winter season, relatively to the quantity poured from its source,
more heat penetrates the uncovered soil, than during the spring or summer.
There is a constant tendency to an equilibrium; and, during the night, the
surface is robbed of more heat, by the colder air, than by day; as, when the
earth is not receiving heat, it is constantly radiating it back into space. Even
in these processes of convection and radiation, a similar law prevails to that
which is discovered in examining into the rate of calorific absorption.
Every tree spreading its green leaves to the sunshine, or exposing its brown
branches to the air—every flower which lends its beauty to the earth—
possesses different absorbing and radiating powers. The chalice-like cup of
the pure white lily floating on the lake—the variegated tulip—the brilliant
anemony—the delicate rose—and the intensely coloured peony or dahlia—
have each powers peculiar to themselves for drinking in the warming life-
stream of the sun, and for radiating it back again to the thirsting
atmosphere. These are no conceits of a scientific dreamer; they are the

truths of direct induction; and, by experiments of a simple character, they
may be put to a searching test.[50]
A thermometric examination of the various coloured flowers, by enclosing a
delicate thermometer amongst their leaves, will readily establish the
correctness of the one; and by a discovery of recent date, connected with
calorific radiation, which must be particularly described presently, we can,
with equal ease and certainty, test the truth of the other;[51] the absorption
and radiation of heat being directly regulated by the colours of the surfaces
upon which the sun rays fall.
It follows, as a natural consequence of the position of the sun, as it regards
any particular spot on the earth at a given time, that the amount of heat is
constantly varying during the year. This variation regulates the seasons.
When it is remembered that the earth is, in the winter, nearly three millions
of miles nearer the sun than in the summer, some explanation is required to
account for our suffering more cold when nearer the source of heat, than
when at the remotest distance.
The earth in her path around the sun describes an ellipse, the sun’s place
being one of its foci. In obedience to the law, already described, of the
conservation of the axis of rotation, the axis of the earth constantly points
towards the star in the constellation of the Little Bear. Recollecting this, and
also the two facts, that a dense solid body absorbs heat more readily than a
fluid one, and that radiation from the surface is constantly going on when
absorption is not taking place, let us follow the earth in her orbit.
It is the time of the vernal equinox—we have equal day and night—
therefore the periods of absorption and radiation of heat are alike. But at
this time of the year the southern hemisphere is opposite to the sun,
consequently the degree of absorption by the wide-spread oceans small.
It is the summer solstice—we have sixteen hours of daylight, when the
absorption of heat is going on—and but eight hours of night, during which
heat is passing off. The northern hemisphere is now presented to the sun,
and as here we have the largest portion of dry land, the powers of
absorption are at their maximum.
The autumnal equinox has arrived, with its equal day and night, as in the
spring, but now the whole northern hemisphere is opposite the sun; hence,

according to the laws already explained, we see the causes of the increased
heat of the autumnal season.
The winter solstice has come, with its long night and shortened day. The
time during which radiation is going on is nearly twice that in which
absorption takes place, and the earth is in her worst position for receiving
heat, as that half which has the largest surface of water is towards the sun.
These are the causes which lead to the variations of the seasons, and
through these we learn why we are colder when near the sun than when at a
considerably greater distance.
An analysis of the spectrum shows us that there are some changes regularly
taking place in the state of the solar beam, which cannot be referred to the
mere alteration of position. It may be inferred, from facts by long-continued
observations, that the three classes of phenomena—light, heat, and
chemical power, distinguished by the term Actinism—which we detect in
the sun’s rays, are constantly changing their relative proportions. In spring,
the chemical agency prevails; in summer, the luminous principle is the most
powerful; and in the autumn, the calorific forces are in a state of the greatest
activity.[52] The importance of these variations, to the great economy of
vegetable life, will be shown when we come to examine the phenomena
connected with organisation.
A remarkable change takes place in the character of heat in being reflected
from material substances. In nature we often see this fact curiously
illustrated. Snow which lies near the trunks of trees or wooden poles melts
much quicker than that which is at a distance from them, the sun shining
equally on both—the liquefaction commencing on the side facing the sun,
and gradually extending. We see, therefore, that the direct rays of solar heat
produce less effect upon the snow than those which are radiated from
coloured surfaces. By numerous experiments, it has been shown that these
secondary radiations are more abundantly absorbed by snow or white
bodies than the direct solar rays themselves. Here is one of the many very
curious evidences, which science lays open to us, of the intimate connection
between the most ethereal and the grosser forms of matter. Heat, by
touching the earth, becomes more earth-like. The subtile principle which,
like the spirit of superstition, has the power of passing, unfelt, through the
crystal mass, is robbed of its might by embracing the things of earth; and

although it still retains the evidences of its refined origin, its movements are
shackled as by a clog of clay, and its wings are heavy with the dust of this
rolling ball. It has, however, acquired new properties, which fit it for the
requirements of creation, and by which its great tasks are facilitated. Matter
and heat unite in a common bond, and, harmoniously pursuing the
necessities of some universal law, the result is the extension of beautiful
forms in every kingdom of nature.
An easy experiment pleasingly illustrates this remarkable change. If a
blackened card is placed upon snow or ice in the sunshine, the frozen mass
underneath it will be gradually thawed, and the card sink into it, while that
by which it is surrounded, although exposed to the full power of solar heat,
is but little disturbed. If, however, we reflect the sun’s rays from a metal
surface, an exactly contrary result takes place; the uncovered parts are the
first to melt, and the blackened card stands high above the surrounding
portion.
The evidences of science all indicate the sun as the source, not only of that
heat which we receive directly through our atmosphere, but even of that
which has been stored by our planet, and which we can, by several
methods, develope. We have not to inquire if the earth was ever an intensely
heated sphere;—this concerns not our question; as we should, even were
this admitted, still have to speculate on the origin—the primitive source of
this caloric.
Before, however, we proceed to the examination of the phenomena of
terrestrial heat, a few of the great results of the laws of radiation and
convection claim our attention.
Nearly all the heat which the sun pours upon the ocean is employed in
converting its water into vapour at the very surface, or is radiated back from
it, to perform the important office of producing those disturbing influences
in the atmosphere, which are essential to the preservation of the healthful
condition of the great aërial envelope in which we live.
Currents of air are generally due to the unequal degrees in which the
atmosphere is warmed. Heat, by expanding, increases the elasticity, and
lessens the density, of a given mass. Consequently, the air heated by the
high temperature of the tropics, ascends charged with aqueous vapours,
whilst the colder air of the temperate and the frigid zones flows towards the

equator to supply its place. These great currents of the atmosphere are,
independent of the minor disturbances produced by local causes, in constant
flow, and by them a uniformity of temperature is produced, which could not
in any other way be accomplished. By these currents, too, the equalisation
of the constituents of the “breath of life” is effected, and the purer oxygen
of the “land of the sunny south” is diffused in healthful gales over the
colder climes of the north. The waters, too, evaporated from the great
central Atlantic Ocean, or the far Pacific, are thus carried over the wide-
spread continents, and poured in fertilising showers upon distant lands.
How magnificent are the operations of nature! The air is not much warmed
by the radiations of caloric passing from the sun to the earth; but the surface
soil is heated by its power of absorbing these rays. The temperature of the
air next the earth is raised, and we thus have the circulation of those
beneficial currents which are so remarkably regular in the Trade Winds. The
air heated within the tropics would ascend directly to the poles, were the
earth at rest, but being in motion, those great aërial currents—the Trade
Winds—are produced, and the periodical monsoons are due to the same
cause. A similar circulation, quite independent of the ordinary tidal
movement, takes place also in the earth-girdling ocean. The water, warmed,
by convection, from the hot surface of the tropical lands, sets across the
Atlantic from the Gulf of Mexico; and being under the influence of the two
forces—gravity and motion—it illustrates the parallelogram of forces, and
flowing along the diagonal, reaches our own shores: the genial influences of
the gulf stream produce that tempered climate which distinguishes our
insular home. Here we have two immense influences produced by one
agency, rendering those parts of the earth habitable and fertile, which but
for these great results would sorrow in the cheerless aspect of an eternal
winter.
The beautiful phenomenon of the formation of dew is also distinctly
connected with the peculiar properties which we have been studying. When
from the bright blue vault of heaven, the sparkling constellations shower
their mild light over the earth, the flowers of the garden and the leaves of
the forest become moist with a fluid of the most translucid nature. Well
might the ancients imagine that the dews were actually shed from the stars;
and the alchemists and physicians of the middle ages conceive that this pure
distillation of the night possessed subtile and penetrating powers beyond

most other things; and the ladies of those olden times endeavour to preserve
their charms in the perfection of their youthful beauty through the
influences of washes procured from so pure a source.[53]
Science has removed the veil of mystery with which superstition had
invested the formation of dew; and, in showing to us that it is a
condensation of vapour upon bodies according to a fixed law of radiation, it
has also developed so many remarkable facts connected with the characters
of material creations, that a much higher order of poetry is opened to the
mind than that which, though beautiful, sprang merely from the
imagination.
Upon the radiation of heat depends the formation of dew, and bodies must
become colder than the atmosphere before it will be deposited upon them.
At whatever temperature the air may be, it is charged to saturation with
watery vapour, the quantity varying uniformly with the temperature.
Supposing the temperature of the air to be 70° F., and that a bottle of water
at 60° is placed in it, the air around the bottle will be cooled, and will
deposit on the glass exactly that quantity of moisture which is due to the
difference between the temperature of the two bodies. Different substances,
independent of colour, have the property of parting with heat from their
surfaces at different rates. Rough and porous surfaces radiate heat more
rapidly than smooth ones, and are consequently reduced in temperature;
and, if exposed, are covered with dew sooner than such as are smooth and
dense. The grass parterre glistens with dew, whilst the hard and stony walk
is unmoistened.[54]
Colourless glass is very readily suffused with dampness, but polished
metals are not so, even when dews are heavily condensed on other bodies.
To comprehend fully the phenomena of the formation of dew, we must
remember that the entire surface of the earth is constantly radiating heat
into space; and that, as by night no absorption is taking place, it naturally
cools.[55] As the substances spread over the earth become colder than the
air, they acquire the power of condensing the vapour with which the
atmosphere is always charged. The bodies which cover this globe are very
differently constituted; they possess dissimilar radiating powers, and
consequently present, when examined by delicate thermometers, varying
degrees of temperature. By the researches of Dr. Wells,[56] which may be

adduced as an example of the best class of inductive experiments, we learn
that the following differences in sensible heat were observed at seven
o’clock in the evening:—
The air four feet above the grass 60–3/4
Wool on a raised board 54–1/2
Swandown on ditto 53
The surface of the raised board 57
Grass plat 51
Dew is most abundantly deposited on clear, calm nights, during which the
radiation from the surface of the earth is uninterrupted. The increased cold
of such nights over those obscured by clouds is well known. The clouds, it
has been proved, act in the same way as the screens used by gardeners to
protect their young plants from the frosts of the early spring, which obstruct
the radiation, and, in all probability, reflect a small quantity of heat back to
the earth.
It is not improbable that the observed increase in grass crops, when they
have been strewn with branches of trees or any slight shades, may be due to
a similar cause.[57]
There are many remarkable results dependent entirely on the colours of
bodies, which are not explicable upon the idea of difference in mechanical
arrangement. We know that different colours are regulated by the powers
which structures have of absorbing and reflecting light; consequently a blue
surface must have a different order of molecular arrangement from a red
one. But there are some physical peculiarities which also influence heat
radiation, quite independently of this surface condition. If we take pieces of
red, black, green, and yellow glass, and expose them when the dew is
condensing, we shall find that moisture will show itself first on the yellow,
then on the green glass, and last of all upon the black or red glasses. The
same thing takes place if we expose coloured fluids in white glass bottles or
troughs, in which case the surfaces are all alike. If against a sheet of glass,
upon which moisture has been slightly frozen, we place glasses similarly
coloured to those already described, it will be found that the earliest heat-
rays will so warm the red and the black glasses, that the ice will be melted

opposite to them, long before any change will be seen upon the frozen film
covered by the other colours.
The order in which heat permeates coloured media, it has already been
shown, very nearly agrees with their powers of radiation.
These most curious results have engaged the attention of Melloni, to whose
investigations we owe so much; and from the peculiar order of radiations,
which present phenomena of an analogous character to those of the
coloured rays of light, obtained by him from dissimilarly coloured bodies,
he has been led to imagine the existence of a “heat-colouration.” That is, the
heat-rays are supposed to possess properties like luminous colour although
invisible; and, consequently, that a blue surface has a strong affinity for the
blue heat-rays, a red surface for the red ones, and so on through the scale.
The ingenuity of this hypothesis has procured it much attention; but now,
when the Newtonian hypothesis of the refrangibility of light is nearly
overturned, we must not, upon mere analogy, rush to the conclusion that the
rays of heat have different orders of refrangibility, which Melloni’s
hypothesis requires.[58]
Can anything be more calculated to impress the mind with the
consciousness of the high perfection of natural phenomena, than the fact,
that the colour of a body should powerfully influence the transmission of a
principle which is diffused through all nature, and also determine the rate
with which it is to pass off from its surface. Some recent experiments have
brought us acquainted with other facts connected with these heat-radiations,
and the power of heat, as influenced by the calorific rays, to produce
molecular changes in bodies, which bear most importantly on our subject.
If we throw upon a plate of polished metal a prismatic spectrum (deprived,
as nearly as possible, of its chemical power, by being passed through a deep
yellow solution—which possesses this property in a very remarkable
manner, as will be explained when we come to the examination of the
chemical action of the sun’s rays)—it will be found, if we afterwards
expose the plate to the action of vapour, very slowly raised from mercury,
that the space occupied by the red rays, and those which lie without the
spectrum below it, will condense the vapour thickly, while the portion
corresponding with the other rays will be left untouched. This affords us
evidence of the power of solar heat to produce, very readily, a change in the

molecular structure of solid bodies. If we allow the sun’s rays to permeate
coloured glasses, and then fall upon a polished metallic surface, the result,
on exposing the plate to vapourisation, will be similar to that just described.
Under yellow and green glasses no vapour will be condensed; but on the
space on which the rays permeating a red glass, or even a blackened one,
fall, a very copious deposit of vapour will mark with distinctness the spaces
these glasses covered. More remarkable still, if these or any other coloured
bodies are placed in a box, and a polished metal plate is suspended a few
lines above them, the whole being kept in perfect darkness for a few hours,
precisely the same effect takes place as when the arrangement is exposed to
the full rays of the sun. Here we have evidence of the radiating heat of
bodies, producing even in darkness the same phenomena as the transmitted
heat-rays of the sun. We must, however, return to the examination of some
of these and other analogous influences under the head of actino-chemistry.
From these curious discoveries of inductive research we learn some high
truths. Associated with light—obeying many of the same laws—moving in
a similar manner—we receive a power which is essential to the constitution
of our planet. This power is often manifested in such intimate combination
with the luminous principle of the solar rays, that it has been suspected to
be but another form of the same agency. While, however, we are enabled to
show the phenomena of one without producing those which distinguish the
other, we are constrained to regard heat as something dissimilar to light. It
is true that we appear to be tending towards some point of proof on this
problem; but we are not in a position to declare them to be forms of one
common power, or “particular solutions of one great physical equation.”[59]
In many instances it would certainly appear that one of these forces was
directly necessary to the production of the other; but we have also
numerous examples in which they do not stand in any such correlation.
We learn, from the scientific facts which we have been discussing, a few of
the secrets of natural magic. In their relations to heat, every flower, which
adds to the adornment of the wilds of nature or the carefully-tended garden
of the florist, possesses a power peculiar to itself;

“Naiad-like lily of the vale,”

and,

“—— The pied wind-flowers, and the tulip tall,
And narcissi, the fairest among them all,”

are, by their different colours, prevented from ever having the same
temperatures under the same sunshine.
Every plant bears within itself the measure of the heat which is necessary
for its well-being, and is endued with functions which mutely determine the
relative amount of dew which shall wet its coloured leaves. Some of the
terrestrial phenomena of this remarkable principle will still further illustrate
the title of this volume.
To commence with the most familiar illustrations, let us consider the
consequences of change of temperature. However slight the additional heat
may be to which a body is subjected, it expands under its influence;
consequently, every atom which goes to form the mass of the earth moves
under the excitation, and the first heat ray of the morning which touches the
earth’s surface, sets up a vibration which is continued as a tremor to its very
centre. The differences between the temperature of day and night are
considerable; therefore all bodies expand under the influence of the higher,
and contract under that of the lower temperature. During the day, any cloud
obscuring the sun produces, in every solid, fluid, or aëriform body, within
the range of solar influence, a check: the particles which had been
expanding under the force of heat suddenly contract. Thus there must of
necessity be, during the hours of sunshine, a tendency in all bodies to dilate,
and during the hours of night they must be resuming their original
conditions.
Not only do dissimilar bodies radiate heat in different degrees, but they
conduct it also with constantly varying rates. Heat passes along silver or
copper with readiness, compared to its progress through platinum. It is
conducted by glass but slowly, and still more slowly by wood and charcoal.
We receive some important intimations of the molecular structure of matter,
from those experiments which prove that heat is conducted more readily
along some lines than others. In some planes, wood and other substances
are better conductors than in others. The metallic oxides or earths are bad

conductors of heat, by which provision the caloric absorbed by the sun’s
rays is not carried away from the surface of this planet so rapidly as it
would have been had it been of metal, but is retained in the superficial crust
to produce the due temperature for healthful germination and vegetable
growth. The wool and hair of animals are still inferior conductors, and thus,
under changes of climate and of seasons, the beasts of the field are secured
against those violent transitions from heat to cold which would be fatal to
them. Hair is a better conductor than wool: hence, by nature’s alchemy, hair
changed into wool in the animals of some countries on the approach of
winter, and feathers into down.
It is therefore evident that the rate at which solar heat is conducted into the
crust of the earth must alter with the condition of the surface upon which it
falls. The conducting power of all the rocks which have been examined is
found to vary in some degree.[60]
It follows, as a natural consequence of the position of the sun to the earth,
that the parts near the equator become more heated than those remote from
it. As this heat is conducted into the interior of the mass, it has a tendency to
move to the colder portions of it, and thus the heat absorbed at the equator
flows towards the poles, and from these parts is carried off by the
atmosphere, or radiated into space. Owing to this, there is a certain depth
beneath the surface of our globe at which an equal temperature prevails, the
depth increasing as we travel north or south from the equator, and
conforming to the contour of the earth’s surface, the line sinking under the
valleys and rising under the hills.[61]
A question of great interest, in a scientific point of view, is the temperature
of the centre of the earth. We are, of course, without the means of solving
this problem; but we advance a little way onwards in the inquiry by a
careful examination of subterranean temperature at such depths as the
enterprise of man enables us to reach. These researches show us, that where
the mean temperature of the climate is 50°, the temperature of the rock at 59
fathoms from the surface is 60°; at 132 fathoms it is 70°; at 239 fathoms it
is 80°: being an increase of 10° at 59 fathoms deep, or 1° in 35·4 feet; of
10° more at 73 fathoms deeper, or 1° in 43·8 feet; and of 10° more at 114
fathoms still deeper, or 1° in 64·2 feet.[62]

Although this would indicate an increase to a certain depth of about one
degree in every fifty feet, yet it would appear that the rate of increase
diminishes with the depth. It appears therefore probable, that the heat of the
earth, so far as man can examine it, is due to the absorption of the solar rays
by the surface. The evidences of intense igneous action at a great depth
cannot be denied, but the doctrine of a cooling mass, and of the existence of
an incandescent mass, at the earth’s centre, remains but one of those
guesses which active minds delight in. The mean annual temperature of this
planet is subject to variations, which are probably dependent upon some
physical changes in the sun himself, or in the atmospheric envelope by
which that orb is surrounded. The variations over the earth’s surface are
great. At the equator we may regard the temperature as uniformly existing
at 80°, while at the poles it is below the freezing point of water; and as far
as observations have been made, the subterranean temperatures bear a close
relation to the thermic condition of the climate of the surface. The
circulation of water through faults or fissures in the strata is, without doubt,
one means of carrying heat downwards much quicker than it would be
conducted by the rocks themselves. It is not, however, found that the
quantity of water increases with the depth. In the mines of Cornwall, unless
where the ground is very loose, miners find that, after about 150 fathoms
(900 feet), the quantity of water rapidly diminishes. That water must ascend
from very much greater depths is certain, from the high temperatures at
which many springs flow out at the surface. In the United Mines in
Cornwall, water rises from one part of the lode at 90°; and one of the levels
in these workings is so hot that, notwithstanding a stream of cold water is
purposely brought into it to reduce the temperature, the miners work nearly
naked, and will bathe in water at 80° to cool themselves. At the bottom of
Tresavean Mine, in the same county, about 320 fathoms from the surface,
the temperature is 100°.
One cause of the great heat of many of our deep mines, which appears to
have been entirely lost sight of, is the chemical action going on upon large
masses of pyritic matter in their vicinity. The heat, which is so oppressive in
the United Mines, is, without doubt, due to the decomposition of immense
quantities of the sulphurets of iron and copper known to be in this condition
at a short distance from these mineral works.

The heat which man is enabled to measure beneath the earth’s surface,
appears to be alone due to the conducting powers of the rocks themselves; it
has been observed that the line of equal temperature follows, as nearly as
possible, the elevations and depressions which prevail upon the surface, and
the diminishing rate of increase beyond this line, certainly is such as would
arise, was all the heat so measured, the result of the passage of the heat by
conduction through the crust of rocks.
Whether or not the subterranean bands of equal heat have any strict relation,
upon a large scale, to the isothermic lines which have been traced around
most portions of our globe, is a point which has not yet been so
satisfactorily determined as to admit of any general deductions.
The Oriental story-teller makes the inner world a place of rare beauty—a
cavern temple, bestudded with self-luminous gems, in which reside the
spiritual beings to whom the direction of the inorganic world is confided.
The Philosopher, in the height of his knowledge, has had dreams as absurd
as this; and amid the romances of science, there are not to be found any
more strange visions than those which relate to the centre of our globe. At
the same time it must be admitted, that many of the peculiar phenomena
which modern geological researches have brought to light, are best
explained on the hypothesis of a cooling sphere, which necessarily involves
the existence of a very high temperature towards the centre.
We have already noticed some remarkable differences between solar and
terrestrial heat; but a class of observations by Delaroche[63] still requires our
attention. Solar heat passes freely through colourless glass, whereas the
radiations from a bright fire or a mass of incandescent metal are entirely
obstructed by this medium. If we place a lamp or a ball of glowing hot
metal before a metallic reflector, the focus of accumulated heat is soon
discovered; but if a glass mirror be used, the light is reflected, but not the
heat; whereas, with the solar rays, but little difference is detected, whether
vitreous or metallic reflectors are employed. It is well known that glass
lenses refract both the light and heat of the sun, and they are commonly
known as burning-glasses: the heat accumulated at their focal point being of
the highest intensity. If, instead of the solar beam, we employ, in our
experiments, an intense heat produced by artificial means, the passage of it
is obstructed, and the most delicate thermometers remain undisturbed in the

focus of the lens. Glass exposed in front of a fire becomes warm, and by
conduction the heat passes through it, and a secondary radiation takes place
from the opposite side.[64] It has been found that glass is transcalescent, or
diathermic, to some rays of terrestrial heat, and adiathemic, or opaque for
heat, to others[65]—that the capability of permeating glass increases with
the temperature of the ignited body—and that rays which have passed one
screen traverse a second more readily. It would, however, appear that
something more than a mere elevation of temperature is necessary to give
terrestrial heat-radiations the power of passing through glass screens, or, in
other words, to acquire the properties of solar heat.
To give an example. The heat of the oxy-hydrogen flame is most intense,
yet glass obstructs it, although it may be assisted by a parabolic reflector. If
this flame is made to play upon a ball of lime, by which a most intense light
is produced, the heat, which has not been actually increased, acquires the
power of being refracted by a glass lens, and combustible bodies may be
ignited in its focus.
It certainly appears from these results, that the undulatory hypothesis holds
true, so far as the motion of the calorific power is concerned. At a certain
rate the vibrations are thrown back or stopped by the opposing body, while
in a state of higher excitation, moving with increased rapidity, they
permeate the screen.[66] This does not, indeed, interfere with the refined
theory of Prévost,[67] which supposes a mutual and equal interchange of
caloric between all bodies.
The most general effect of heat is the expansion of matter; solids, liquids,
and airs, all expand under its influence. If a bar of metal is exposed to
calorific action, it increases in size, owing to its particles being separated
farther from each other: by continuing this influence, after a certain time the
cohesion of the mass is so reduced that it melts, or becomes liquid, and,
under the force of a still higher temperature, this molten metal may be
dissipated in vapour. It would appear as if, under the agency of the heat
applied to a body, its atoms expanded, until at last, owing to the tenuity of
the outer layer or envelope of each atom, they were enabled to move freely
over each other, or to interpenetrate without difficulty. That heat does really
occasion a considerable disturbance in the corpuscular arrangement of
bodies, may be proved by a very interesting experiment. A bar of heated

metal is placed to cool, with one end supported upon a wedge or a ring of a
different metal the other resting on the ground. In cooling, a distinct musical
sound is given out, owing to the vibratory action set up among the particles
of matter moving as the temperature declines.[68]
Heat is diffused through all bodies in nature, and, as we shall presently see,
may be developed in many different ways. We may, therefore, infer, that in
converting a sphere of ice into water, and that again into steam, we have
done nothing more than interpenetrate the mass with a larger quantity of
heat, by which its atoms are more widely separated, and that thus its
molecules become free to move about each other. Hence, from a solid state,
the water becomes fluid; and then, if the expansive force is continued, an
invisible vapour. If these limits are passed by the powers of any greatly
increased thermic action, the natural consequence, it must be seen, will be
the separation of the atoms from each other, to such an extent that the
molecule is destroyed, and chemical decomposition takes place.
By the agency of the electricity of the voltaic battery, we are enabled to
produce the most intense heat with which we are acquainted, and by a
peculiarly ingenious arrangement Mr. Grove has succeeded in resolving
water by the mere action of heat into its constituent elements—oxygen and
hydrogen gases. That this decomposition is not due to the voltaic current,
but to the heat produced by it, was subsequently proved by employing
platina heated by the oxy-hydrogen flame.[69]
This interesting question has been examined with great care by Dr.
Robinson of Armagh, who has shown that, as the temperature of water is
increased, the affinity of its elements is lessened, until at a certain point it is
eventually destroyed. This new and startling fact appears scarcely consistent
with our knowledge that a body heated so as to be luminous has the power
of causing the combination of the elements of water with explosive
violence.[70] But as this acute experimental philosopher somewhat boldly
but still most reasonably inquires: “Is it not probable that, if not light, some
other actinic power (like that which accompanies light in the spectrum, and
is revealed to us by its chemical effects in the processes of photography) is
evolved by the heat, and, though invisible, determines, in conjunction with
the affinity, that atomic change which transforms the three volumes of
oxygen and hydrogen into two of steam?”[71]

This speculation explains, in a very satisfactory manner, some results which
were obtained by Count Rumford, in 1798. In a series of experiments
instituted for the purpose of examining “those chemical properties of light
which have been attributed to it,” he has shown that many cases of chemical
decomposition occur in perfect darkness, under the influence of heat, which
are precisely similar to those produced by exposure to the sun’s rays.[72]
It must, however, be remembered, that both solar light and heat are
sometimes found in direct antagonism to actinic power, and that the most
decided chemical changes are produced by those rays in which neither heat
nor light can be detected. The most remarkable phenomena of this class will
be explained under the head of actinism.
One of the most curious relations which as yet have been discovered
between light and heat is, that, the temperature at which all bodies become
incandescent, excepting such as are phosphorescent, is uniform. The point
on the thermometer (Fahrenheit’s scale) when the eye by perfect repose is
enabled to detect the first luminous influence, may probably be regarded as,
or very near, 1000°. Daniel has fixed this point at 980°, Wedgwood at 947°,
and Draper at 977°.[73] Dr. Robinson and Dr. Draper, by independent
observations, have both arrived at the conclusion, that the first gleam of
light which appears from heated platina is not red, but of a lavender gray,
the same in character of colour as that detected by Sir John Herschel among
the most refrangible rays of the solar spectrum.[74]
It must be admitted, that the question of the identity, or otherwise, of light
and radiant heat, is beset with difficulties. Many of their phenomena are
very similar—many of their modes of action are alike: they are often found
as allied agencies; but they as frequently exhibit extreme diversity of action,
and they may be separated from each other.
We have now examined the physical conditions and properties of this most
important element, and we must proceed to learn something of the means
by which it may be developed, independently of its solar source.
This extraordinary principle exists in a latent state in all bodies, and may be
pressed out of them. The blacksmith hammers a nail until it becomes red
hot, and from it he lights the match with which he kindles the fire of his
forge. The iron has by this process become more dense, and percussion will
not again produce incandescence until the bar has been exposed in fire to a

red heat. The only inference we can draw from this result is, that by
hammering the particles have been driven closer together, and the heat
driven out; now further hammering will not force the atoms nearer, and
consequently no additional quantity of heat can be developed; the iron is
made hot in a fire, it absorbs heat, the particles are restored to their former
state, and we can now again by hammering develope both heat and light.
The Indian produces a spark by the attrition of two pieces of wood. By
friction, two pieces of ice may be made to melt each other; and could we,
by mechanical pressure, force water into a solid state, an immense quantity
of heat would be set free. By the condensation of hydrogen and oxygen
gases, pulverulent platinum will become glowing red-hot, and, with certain
precautions, even the compact metal, platinum, itself; the heat being derived
from the gases, the union of which it has effected. A body passing from the
solid to the fluid state absorbs heat from all surrounding substances, and
hence a degree of cold is produced. The heat which is thus removed is not
destroyed—it is held combined with the fluid; it exists in a latent state.
Fluids, in passing into a gaseous form, also rob all surrounding bodies of an
amount of heat necessary to maintain the aëriform condition. From the air
or from the fluid, this heat may, as we have shown above, be again
extracted. Locked in a pint measure of air, there exists sufficient heat to
raise several square inches of metal to glowing redness. By the compression
of atmospheric air this may be shown, and with a small condensing syringe
a sufficient quantity of heat may be set free to fire the Boletus igniarius,
which, impregnated with nitre, is known as amadou. We are acquainted
with various sources from which heat may be developed for artificial
purposes: the flint-and-steel is an example of the production of heat by
mechanical force, and the modern lucifer-match, of the combined action of
friction and chemical affinity. These of themselves would admit of a
lengthened discourse; but it is necessary that we carefully examine some of
the less familiar phenomena of heat under the influences of changes of
chemical condition.
If spirits of wine and water are mixed together, a considerable degree of
heat is given out, and by mixing sulphuric acid and water, an infinitely
larger quantity. If sulphuric acid (oil of vitriol) and spirit of wine, or nitric
acid (aquafortis) and spirits of turpentine, at common temperatures, be
suddenly mixed, so much heat is set free as to ignite the spirit. In each of
these instances there is a condensation of the fluid. In nearly all cases of

solution, cold is produced by the absorption of the heat necessary to sustain
the salt in a liquid form; but when potash dissolves in water, heat is given
out, which is a fact we cannot yet explain. If potassium is placed on water,
it seizes the oxygen of the water and sets fire to the hydrogen gas liberated
by the heat produced in the change of form. Antimony and many other
metals thrown into chlorine gas ignite and burn with brilliancy: the same
phenomenon takes place in the vapours of iodine or bromine. Many
chemical combinations, as the chloride of potassium and sulphur explode
with a blow; whilst the slightest friction occasions the detonation of the
fulminating salts of silver, mercury, and gold. Compounds of nitrogen and
chlorine, or iodine, are still more delicately combined—the former
exploding with fearful violence on the contact of any oleaginous body, and
the latter by the smallest elevation of temperature: both of them destroying
the vessels in which they may be contained.
Gun cotton presents some peculiar phenomena which may merit brief
attention. This peculiar compound is prepared by the action of nitric acid on
cotton fibre. The general appearance of the cotton is not altered, but a
remarkable physical change has taken place. It is now soluble in ether, and
forms a gelatinous compound:—it explodes violently at a temperature
which is insufficient for the combustion of gunpowder. Indeed, from, as it
would appear, slight electrical disturbances taking place in the gun cotton
itself, it not unfrequently explodes spontaneously. These fearful
disturbances of the forces which hold bodies in combination are explained
with difficulty. May it not be, that an enormous quantity of the calorific and
chemical principles is held in a state of extreme tension around the particles
of the compound, and that the equilibrium being destroyed, the whole is
developed in destructive rapidity?
The fact of great heat being evolved during the conversion of a body from a
solid to a gaseous state, as in the explosion of gunpowder or gun cotton,
which is a striking exception to the law of latent heat, as it prevails in most
cases, admits of no more satisfactory explanation.
As mechanical force produces calorific excitation, so we find that every
movement of sap in vegetables, and of the blood and fluids in the animal
economy, causes a sensible increase of heat. The chemical processes
constantly going on in plants and animals are another source of heat, in
addition to which nervous energy and muscular movement must be

regarded as producing the caloric which is essential to the health and life of
the latter. Digestion has been considered as a process of combustion; and
the action between the elements of food, and the oxygen conveyed by the
circulation of the blood to every part of the body, regarded as the source of
animal heat; and, without doubt, it is one great source, although it can
scarcely be regarded as the only one.[75]
The vis vitæ, or vital power, influences the delicate and beautiful system of
nerves; and as life (an essence of the rarest and most subtile order, a
diffusive influence) runs through them, from the brain to the extremities of
the members of the body, it sets those tender threads in rapid vibration, and
heat is developed. By this action, the circulation of the blood is effected; the
muscle is maintained in an elastic condition, ready to perform the tasks of
the will; and through these agencies is the warm and fluid blood fitted to
receive its chemical restoratives in the lungs, and the stomach to support
changes for which it is designed—chemical also—by which more heat is
liberated. Was digestion—Eremacausis, as the slow combustion produced
by combination with oxygen is called—the only source of animal heat, why
should the injury of one filmy nerve place a member of the body for ever in
the condition of stony coldness? Or why, chemical action being most
actively continued after a violent death, by the action of the gastric juices
upon the animal tissues, should not animal heat be maintained for a much
longer period than it is found to be after respiration has ceased?[76]
In studying the influences of caloric upon the conditions of matter, we must
regard the effects of extreme heat, and also of the greatest degrees of cold
which have been obtained.
There are a set of experiments by the Baron Cagniard de la Tour, which
appear to have a very important bearing on some conditions that may be
supposed to prevail in nature, particularly if we adopt the view of a
constantly increasing temperature towards the centre of our earth. If water,
alcohol, or ether, is put into a strong glass tube of small bore, the ends
hermetically sealed, and the whole exposed to a strong heat, the fluid
disappears, being converted into a transparent gas; but, upon cooling, it is
again condensed, without loss, into its original fluid state.[77] In this
experiment, fluid bodies have been converted into elastic transparent gases
with but small change of volume, under the pressure of their own

atmospheres. We can readily conceive a similar result occurring upon a far
more extensive scale. In volcanic districts, at great depths, and consequently
under the pressure of the superincumbent mass, the siliceous rocks, or even
metals, may, from the action of intense heat, be brought into a fluid, or even
a gaseous condition, without any change of volume, since the elastic force
of heat is opposed by the rigid resistance of the pressure of the surrounding
rocks. Some beautiful experiments by Mr. Hopkins, of Cambridge, have
proved that the temperature necessary to melt a body must be considerably
elevated as the mechanical pressure to which it is subjected is increased.
Directly connected with the results of Cagniard de la Tour are a yet more
remarkable set of phenomena, which have been investigated by M.
Boutigny,[78] and generally known as the “spheroidal condition” of bodies.
If water is projected upon very hot metal it instantly assumes a spheroidal
form—an internal motion of its particles may be observed—it revolves with
rapidity, and evaporates very slowly. If a silver or platinum capsule, when
brought to a bright red heat, is filled with cold water, the whole mass
assumes the spheroidal state, the temperature of the fluid remaining
considerably below the boiling point, so long as the red heat is maintained.
If we allow the vessel to cool below redness in the dark, the water then
bursts into active ebullition, and is dissipated into vapour with almost
explosive violence. An equal quantity of water being projected into two
similar vessels, over the fire, one cold and the other red hot, it will be found
that the water in the cold vessel will boil and evaporate long before that in
the one which is red hot.
Another form of this experiment is exceedingly instructive. If a mass of
white hot metal is suddenly plunged into a vessel of cold water, the
incandescence is not quenched, the metal shines with a bright white light,
and the water is seen to circulate around, but at some distance from the
glowing mass, being actually repelled by calorific agency. At length, when
the metal cools, the water comes in contact with it, and boils with energy.
A result similar to this was observed by Perkins, but its correctness most
unjustly doubted. Having made an iron shell containing water, and carefully
plugged up, white hot, it was found that the steam never exerted sufficient
force to burst the vessel, as it was expected it would do. He caused a hole to
be drilled into the bottom of the white-hot shell, and he was surprised to
find that no water flowed through the orifice, until the iron was

considerably cooled, when it issued forth with violence in the form of
steam. Here we have the Cagniard de la Tour state first induced, and the
calorific repulsion of the spheroidal state supervenes. If water is poured
upon an iron sieve, the wires of which are made red hot, it will not
percolate; but on cooling, it runs through rapidly. M. Boutigny, pursuing
this curious inquiry, has recently proved that the moisture upon the skin is
sufficient to protect it from disorganization, if the arm is plunged into baths
of melted metal. The resistance of the surfaces is so great, that little
elevation of temperature is experienced.[79] Professor Plücker, of Bonn, has
stated that by washing the arm with ether previously to plunging it into
melted metal, the sensation produced, while in the molten mass, is that of
freezing coldness.
We have now seen that heat at different degrees of intensity appears to
produce chemical composition—that it decomposes combined elements—
that it alters the conditions of bodies, and actually maintains so powerfully a
repellent force, that fluids cannot touch the heated body. More than this, it
exerts a most powerful antagonistic influence over all chemical relations. If,
to give one example, the volatile element iodine is put into a glowing hot
capsule, it resolves itself immediately into a spheroid. Potash rapidly
combines with iodine; but if a piece of this alkali is thrown upon it in the
capsule, it also takes the spheroidal form, and both bodies revolve
independently of each other, their chemical affinities being entirely
suspended;—but allow the capsule to cool, and they combine immediately.
Science teaches us that a temperature so exalted as not to burn organic
bodies may be produced, and points to us this remarkable fact, that the
destructive limits of heat are measured between certain degrees—beyond
which a fire, by reason of its intensity, ceases to develope heat. What is the
radiant force into which this principle changes?
The experiments of Cagniard de la Tour and of Boutigny (d’Evreux),
connect themselves, in a striking manner, with those of Mr. Grove and Dr.
Robinson; and they teach us that but a very slight alteration in the
proportions of the calorific principle given to this planet would completely
change the character of every material substance of which it is composed,
unless there was an alteration in the physical condition of the elements
themselves.

Supposing the ordeal of fiery purification to take place upon this earth,
these experiments appear to indicate the mighty changes which would
thence result. There would be no annihilation, but everything would be
transformed from the centre of the globe to the verge of its atmosphere—
old things would pass away, all things become new, and the beautiful
mythos of the phœnix be realized in the fresh creation.
The deductions to be drawn from the results obtained by abstracting heat
from bodies are equally instructive. By taking advantage of the cooling
produced by the rapid solution of salts of several kinds in water, an intense
degree of coldness may be produced.[80] Indeed, the absorption of heat by
liquefaction may be shown by the use of metallic bodies alone. If lead, tin,
and bismuth, are melted together, and reduced to a coarse powder by being
poured into water, and the alloy then dissolved in a large quantity of
quicksilver, the thermometer will sink nearly 50 degrees. An intense amount
of cold will result from the mixture of muriate of lime and snow, by which a
temperature of 50° below the zero of Fahrenheit, or 82° below the freezing
point of water, is produced. By such a freezing mixture as this, mercury will
be rendered solid. A degree of cold, however, far exceeding it, has lately
been obtained by the use of solid carbonic acid and ether.[81] Solid carbonic
acid is itself procured from the gas liquefied by pressure; which liquid,
when allowed to escape into the air, evaporates so rapidly that a large
quantity of it is congealed by being robbed of its combined heat by the
vaporizing portion. When this solid acid is united with ether, a bath is
formed in which the carbonic acid will remain solid for twenty or thirty
minutes. By a mixture of this kind, placed under the receiver of an air-
pump, a good exhaustion being sustained, a degree of cold 166° below zero
is secured. By this intense cold, many of the bodies which have hitherto
been known to us only in the gaseous state have been condensed into
liquids and solids. Olefiant gas, a compound of hydrogen and carbon, was
brought into a liquid form. Hydriodic and hydrobromic acids could be
condensed into either a liquid or a solid form. Phosphuretted hydrogen, a
gas which inflames spontaneously when brought into contact with the air or
with oxygen, became a transparent liquid at this great reduction of
temperature. Sulphurous acid may be condensed, by pressure and a
reduction of temperature, into a liquid which boils at 14° Fahrenheit, but by
the carbonic acid bath it is converted into a solid body, transparent and

without colour. Sulphuretted hydrogen gas solidifies at 122° below zero,
and forms a white substance resembling a mass of crystals of sea-salt.
A combination of the two gases, chlorine and oxygen, becomes solid at
-75°, and the protoxide of nitrogen at -150°. Cyanogen, a compound of
carbon and nitrogen—the base of prussic acid—is solidified at 30° below
the zero of our thermometric scale. The well-known pungent compound,
ammonia, so exceedingly volatile at common temperatures, is converted
into a crystalline, translucent, white substance at the temperature of -103°.
The difficulties which necessarily attend the exposure of a body to extreme
cold and great pressure at the same time, appear to be the only obstacle to
the condensation of oxygen, hydrogen, and nitrogen gases. A sufficient
amount of condensation was, however, effected by Dr. Faraday, to lead him
to the conclusion, arrived at also by other evidences, that hydrogen, the
lightest of the ponderable bodies, partakes of the nature of a metal.[82]
During the solidification of water by freezing, some remarkable facts may
be noticed.
Water, in cooling, gradually condenses in volume until it arrives at 40°
Fahr., which appears to be the point of greatest density. From this
temperature to that of 32°, the point at which it begins to solidify, its
volume remains unchanged,[82] as crystallisation (freezing) begins, the bulk
increases, the mass becomes specifically lighter, and it swims on the surface
of the fluid. From 40° to 32° the particles of water must be taking up that
new position which is essential to the formation of the solid—ice; and while
this is taking place, every substance held in solution by the water is
rejected.
If we mix with water the deepest colouring matter—the strongest acid or
the most acrid poison—they are each and all rejected during the process of
freezing, and if the water has been kept in a state of agitation during the
process—so that the liberated particles may not be mechanically entangled
—the ice will be transparent, colourless, tasteless, and inert—the substances
rejected being gathered together in the centre of the frozen mass in a state
of intense concentration. In like manner, even the atmospheric air, which is
always held in solution, is rejected, and hence the reason why all the ice
which forms upon still ponds is full of air-bubbles, while the ice which is
produced in agitated water is perfectly free from them. This in itself is a

remarkable condition, the entire bearing of which is not clearly understood;
but a still more singular fact has been discovered in intimate connection
with the rejection of all matter from a freezing solution. Water, which in this
way is freed entirely of air, will not boil at 212° F., the ordinary boiling
point of water.
If a mass of ice formed in the manner described is placed in a vessel, and
being just covered with a film of oil, to prevent the absorption of air, is
melted over a lamp or fire, and the heat continued, it will, so far from being
converted into steam at 212°, continue to increase in temperature up to 270°
or more, and then burst into ebullition with such explosive violence as to
rend the vessel in which it is confined.
From this experiment we learn that did water exist in any other condition
than that in which we find it—even with the apparently simple difference of
containing no air—it would not be safe to employ it in any culinary or
manufacturing operation, since its use would be followed by explosions as
dangerous as those of gunpowder.
Such researches as these prove to us the admirable adaptation of all things
to their especial ends—the beautiful adjustment of the balance of forces
throughout creation.
The refinements of Grecian philosophy saw, without the aids of inductive
science, that the outward vesture of nature covered a host of mysterious
agencies to which its characteristics were directly due. In their dream of the
four elements, fire, the external and visible form of heat, was regarded as
the cause of vitality, and the disposer of every organised and unorganised
condition of matter. Their idealisations have assumed another form, but the
researches of modern science have only established their universality and
truth.
The great agents at work in nature—the mighty spirits bound to never-
ending tasks, which they pursue with unremitting toil, are of so refined a
character, that they will probably remain for ever unknown to us. The arch-
evocator, with the wand of induction, calls; but the only answer to his
evocation is the manifestation of power in startling effects. Science pursues
her inquiries with zeal and care: she tries and tortures nature to compel her
to reveal her secrets. Bounds are, however, set to the powers of mortal
search: we may not yet have reached the limits within which we are free to

exercise our mental strength; but, those limits reached, we shall find an
infinite region beyond us, into which even conjecture wanders eyeless and
aimless, as the blind Cyclops groping in his melancholy cave.[83]
All we know of heat is, that striking effects are produced which we measure
by sensation, and by instruments upon which we have observed that given
results will be produced under certain conditions: of anything approaching
to the cause of these we are totally ignorant. The wonder-working mover of
some of the grandest phenomena in nature—giving health to the organic
world, and form to the inorganic mass—producing genial gales and dire
tornadoes—earthquake strugglings and volcanic eruptions—ministering to
our comforts in the homely fire, and to advancement in civilisation in the
mighty furnace, and the ingenious engine which drains our mines, or
traverses our country with bird-like speed,—will, in all probability, remain
for ever unknown to man. The immortal Newton, many of whose guesses
have a prophetic value, thus expresses himself:—“Heat consists in a minute
vibratory motion in the particles of bodies, and this motion is
communicated through an apparent vacuum by the undulations of a very
subtile elastic medium, which is also concerned in the phenomena of light.”
Our experimental labours and our mathematical investigations have
considerably advanced our knowledge since the time of Newton; yet still
each theory of heat strangely resembles the mystic lamp which the
Rosicrucian regarded as a type of eternal life—a dim and flickering symbol,
in the tongue-like flame of which imagination, like a child, can conjure
many shapes.
Modern theory regards heat as a manifestation of motion, and experiment
proves that a body falling through a certain space generates a definite
quantity of heat, while observation shows that the waters at the base of the
Falls of Niagara possess a temperature 1° higher than when they first glide
over the edge of the precipice.
This increase of temperature is due to the mechanical force due to the fall,
and is no more an evidence of the conversion of motion into heat, than is
the old experiment of rubbing a button until it becomes hot. At all events,
the fact that a given amount of mechanical force always produces an
equivalent of heat is as applicable to the idea of a “subtile elastic medium”

which is diffused through all matter, as to the, at present, favourite
hypothesis.
So far has this view been strained, that the temperature of the planets has
been referred to their motions, and speculation has aided the mathematician
in determining the cessation of planetary motion, by the conversion of it
into heat. It is true that other theorists have supposed points in space upon
which this heat might be concentrated and reflected back again to produce
motion.
There may be much of the poetic element in such speculations, but it is of
that order which belongs rather to the romantic than to the real.
A speculation which has more of truth, and which is, indeed, demonstrable,
cannot fail to impress every mind with its beauty, and probable correctness.
In the growth of a tree, its wood and all its products are the result of certain
external forces effecting chemical changes. Carbonic acid is decomposed,
the carbon is retained, and oxygen given off, and assimilations of a complex
character are in constant progress to produce the various compounds of
oxygen, hydrogen, nitrogen, and carbon.
Every condition of organised forms is due to the external excitation of light
and heat, and in the chemical changes which take place, an equivalent of
these principles, or powers—it signifies but little according to which view
we may regard them—is absorbed, and retained as essential to the condition
of the matter formed. Let us confine our attention to wood—although the
position applies equally to every organic product. A cubic foot of wood is
formed by the decomposition of a certain quantity of carbonic acid, by the
vital function of the plant, excited by the solar rays, which are involved in
the mass which nature by “her wondrous alchemy” has made. Eventually
this cubic foot of wood is subjected to a process of chemical change—
combustion; by the application of a single spark,—and in the disintegration
of the wood, its carbon combining with oxygen to form carbonic acid, its
hydrogen to form water, which is returned to the air, a large amount of light
and heat is produced. This is exactly equivalent to the amount which was
engaged in its formation. Indeed, the sunshine which fell upon the leaves of
the forest tree, of which the log formed a part, has been hoarded up, and we
again develope it in its original state of heat and light.

The vast coal beds of England were formed by the rapid growth and quick
decay of a peculiar class of plants under the influence of a tropical sun.
They have been buried myriads of ages, under hundreds of feet of sandy
rock. By the industry of the miner the coal is brought again to the surface,
and we develope from it those powers by which it was formed.
In the fire which gives comfort to our homes—in the furnace which
generates force for the purposes of manufacture, or to propel the railway
engine and its ponderous train—in the gas with which we illumine our
streets and gladden during the long winter nights our apartments, we are
developing that heat and light which fell upon the earth with all its
quickening influences millions of ages before yet the Creator had called
into existence the monarch Man, for whose necessities these wondrous
formations were designed.

FOOTNOTES:
[43] The following table of the rays penetrating coloured glass has been given by
Melloni, in his memoir On the Free Transmission of Radiant Heat through
Different Bodies:—
Deep violet 53
Yellowish red (flaked) 53
Purple red (flaked) 51
Vivid red 47
Pale violet 45
Orange red 44
Clear blue 42
Deep yellow 40
Bright yellow 34
Golden yellow 33
Deep blue 33
Apple green 26
Mineral green 23
Very deep blue 19
Translated in the Scientific Memoirs, vol. i. p. 30.
[44] “The physical characters of this species of glass, which acts so differently
from the other species of coloured glass in all the phenomena of calorific

absorption, are, 1st, its intercepting almost totally the rays which pass through
alum; 2nd, its entirely absorbing the red rays of the solar spectrum. I have
already stated that their colouration is produced almost entirely by the oxide of
copper.
“Thus, the colouring matters of the coloured glasses, while they so powerfully
affect the relations of quantity which the different rays of ordinary light bear to
each other, exercise no elective action on the concomitant calorific rays. This
curious phenomenon is the more remarkable as the colouring matters absorb
almost always a very considerable portion of the heat naturally transmitted by
the glass. The following are, in fact, the calorific transmissions of the seven
coloured glasses referred to; the transmission of the common glass being
represented by 100; red glass, 82·5; orange, 72·5; yellow, 55; bluish-green, 57·5;
blue, 52·5; indigo, 30; violet, 85. The quantity of heat absorbed through the
action of the colouring substances is, therefore, 17·5 in the red glass, 27·5 in the
orange, 45 in the yellow, 42·5 in the green, 47·5 in the blue, 70 in the indigo,
and 15 in the violet. Now, as these absorptions extinguish a proportional part of
each of the rays which constitute the calorific stream transmitted by common
glass, they may be compared, as we said before, with the absorbent action
exercised on light by matters more or less deeply brown or dark, when they are
immersed in water, or some other colourless liquid which dissolves, but does not
affect them chemically.”—Annales de Chimie et de Physique, tom. xl. p. 382.
Guided by these principles, the author selected the glass employed in glazing the
Royal Palm-House, at Kew Botanical Gardens, where it was desired to obstruct
the passage of those rays which have a particular scorching influence. Of this
glass a description was given at the meeting of the British Association at Oxford,
which appears in the Transactions for that year. The result has been all that could
be desired—not a single instance of scorching having occurred during the three
years which have elapsed.
[45] In the Philosophical Transactions, vol. xc., the following papers, by Sir
William Herschel, may be consulted:—
Investigation of the powers of the prismatic colours to heat and illuminate
objects; with remarks that prove the different refrangibility of radiant heat. To
which is added, an inquiry into the method of viewing the sun advantageously,
with telescopes of large apertures and high magnifying powers, p. 255.
Experiments on the refrangibility of the invisible rays of the sun, p. 284.
Experiments on the solar and on the terrestrial rays that occasion heat; with a
comparative view of the laws to which light and heat, or rather the rays which
occasion them, are subject; in order to determine whether they are the same or
different, pp. 293, 437.
In connection with this inquiry, Sir William Herschel remarks, that since a red
glass stops no less than 692 out of 1,000 such rays as are of the refrangibility of
red light, we have a direct and simple proof, in the case of the red glass, that the
rays of light are transmitted, while those of heat are stopped, and that thus they
have nothing in common but a certain equal degree of refrangibility, which by
the power of the glass must occasion them to be thrown together into the place
which is pointed out to us by the visibility of the rays of light.
On the same subject, a Memoir, by Sir Henry Englefield, in the Journal of the
Royal Institution for 1802, p. 202, may be consulted; and Researches on Light,

by the Author.
[46] Dr. Draper, On the production of light by heat, in the Phil. Mag. for 1847.
Sir Isaac Newton fixed the temperature at which bodies become self-luminous at
635°; Sir Humphry Davy at 812°; Mr. Wedgewood at 947°; and Mr. Daniell at
980°; whilst Dr. Draper from his experiments gives 977°; and Dr. Robinson
865°.
In a review of the above paper by Melloni, entitled Researches on the Radiations
of Incandescent Bodies, and on the Elementary Colours of the Solar Spectrum,
translated for Silliman’s Journal for August, 1847, he remarks:—
“I say that they conduct, as do others heretofore known on light and radiant heat,
to a perfect analogy between the general laws which govern these two great
agents of nature. I will add that I regard the theory of their identity as the only
one admissible by the rules of philosophy; and that I consider myself obliged to
adopt it, until it shall have been proved to me that there is a necessity of having
recourse to two different principles, for the explanation of a series of phenomena
which at present appear to belong to a solitary agent.”
Reference should also be made to a paper by Dr. Robinson, On the effects of
Heat in lessening the Affinities of the Elements of Water, in the Transactions of
the Royal Irish Academy, 1848, where he says that “when a platinum wire is
traversed by a current gradually increased till it produces ignition, the first gleam
that appears is not red, but of a colour which, when I first saw it, I compared to
the ‘lavender ray’ discovered by Sir John Herschel beyond the violet, though I
was surprised at seeing the tint of that most refrangible ray preceding the ray
which is least so. It is quite conspicuous at about 865°; and as the mode in which
it makes its appearance presents nothing abrupt or discontinuous, it seems likely
that it is merely a transition from invisible rays excited at a lower temperature to
ordinary light.”—p. 310.
[47] In the Bakerian Lecture for 1842, On the transparency of the Atmosphere,
and the law of extinction of the solar rays in passing through it, by James D.
Forbes, Esq., F.R.S., &c., will be found a most complete investigation of this
subject.
The experiments were, for the most part, made in Switzerland with Sir John
Herschel’s actinometer, and they prove satisfactorily,—“That the absorption of
the solar rays by the strata of air to which we have immediate access, is
considerable in amount for even moderate thicknesses.”
[48] After referring to several curious and instructive experiments, in which
peculiar chemical changes are produced under the influence of the solar rays by
their Heat, Sir John Herschel says:—
“These rays are distinguished from those of Light by being invisible; they are
also distinguished from the pure calorific rays beyond the spectrum, by their
possessing properties (of a peculiar character, referred to in former papers)
either exclusively of the calorific rays, or in a much higher degree. They may
perhaps not improperly be regarded as bearing the same relation to the calorific
spectrum which the photographic rays do to the luminous ones. If the restriction
to these rays of the term thermic, as distinct from calorific, be not (as I think, in
fact, it is not) a sufficient distinction, I would propose the term parathermic rays

to designate them. These are the rays which I conceive to be active in producing
those singular molecular affections which determine the precipitation of vapours
in the experiments of Messrs. Draper, Moser, and Hunt, and which will probably
lead to important discoveries as to the intimate nature of those forces resident on
the surfaces of bodies, to which M. Dutrochet has given the name of epipolic
forces.”—On certain improvements in Photographic Processes, described in a
former communication (Phil. Trans, vol. cxxxiii.); and On the Parathermic Rays
of the Solar Spectrum, Phil. Trans, vol. cxxxiv.
The experiments of Mrs. Somerville, On the Action of the Rays of the Spectrum
on Vegetable Juices (Phil. Transactions, vol. cxxxvii.), appear to connect
themselves with this particular class of rays in a curious manner.
[49] Experiments on the influence of heat on differently-coloured bodies were
first made by Dr. Hooke; and it was not until long after that Franklin made his
ingenious experiments. Davy exposed to sunshine six equal pieces of copper,
painted white, yellow, red, green, blue, and black, in such a manner that one side
only was illuminated. To the dark side he attached a bit of cerate, ascertained by
experiment to melt at 700. The cerate attached to the black became fluid first,
the blue next, then the green and red, and lastly the yellow and white.—
Beddoes’s Contributions to Physical Knowledge, and collected works of Sir
Humphry Davy, vol. ii. p. 27.
[50] By reference to the Treatise on Heat, in the Encyclopædia Metropolitana,
numerous suggestive experiments will be found, all bearing on this subject.
Peschel’s Elements of Physics may also be consulted with advantage. The fact is,
however, simply proved, as stated in the text, by placing the bulbs of delicate
thermometers, so as to be completely involved in the petals of flowers exposed
to sunshine, shading the upper portion of the stem of the instrument.
[51] Moser, On Vision, and on the Action of Light on Bodies: and also On Latent
Light: Scientific Memoirs, vol. iii. Draper, On certain Spectral Appearances,
and on the Discovery of Latent Light: Phil. Mag., Nov. 1842.
[52] A particular examination of this curious question will be found in the
Author’s report On the Influence of the Solar Rays on the Growth of Plants:
Reports of the British Association for 1847.
[53] Ammianus Marcellinus ascribes the longevity and robust health of
mountaineers to their exposure to the dews of night. Dew was employed by the
alchemists in their experiments on the solution of gold. The ladies of old
collected the “celestial wash,” which they imagined had the virtue of preserving
their fine forms, by exposing heaps of wool to the influences of night radiation.
It was supposed that the lean features of the grasshopper arose from that insect
feeding entirely on dew: “Dumque thymo pascentur apes, dum rore cicadæ,”
Virgil, Eclog.
See some curious remarks by Boyle, On the Power of Dew in Working on Solid
Bodies: Works of the Honourable R. Boyle, vol. v. p. 121. 1744.
[54] See the Researches on Heat, by Professor James Forbes, in the Transactions
of the Royal Society of Edinburgh; also Melloni’s papers on the same subject in
the Annales de Chimie, several of which have been translated into the Scientific
Memoirs, edited by Mr. Richard Taylor.

[55] The phenomena of dew have constantly engaged the attention of man.
Aristotle, in his book De Mundo, puts forth some just notions on its nature. An
opinion has almost always prevailed that dew falls. Gersten appears to have been
the first who opposed this motion. He was followed by Musschenbroek, and then
by Du Fay. The researches of Leslie were of a far more exact character. Dr.
Wilson, in the Transactions of the Royal Society of Edinburgh, 1st vol.,
published a Memoir on Hoar Frost of much interest; but the questions involved
remained unsettled until the researches of Dr. Wells, which were published in his
Essay on Dew.
[56] By far the most complete set of experiments on the radiation of heat from
the surface at night, which have been published since Dr. Wells’s memoir On
Dew, are those of Mr. Glaisher, of the Royal Observatory at Greenwich.
Instruments of the most perfect kind were employed, and the observations made
with sedulous care. The results will be found in a memoir On the Amount of the
Radiation of Heat, at night, from the Earth, and from various bodies placed on
or near the Surface of the Earth, by James Glaisher, Esq., Philosophical Trans.
for 1847, part 2.
[57] Dr. Wells noticed the practical fact that very light shades protected delicate
plants from frost, by preventing radiation. Mr. Goldsworthy Gurney has made a
series of interesting experiments, and he imagines that by shading grasslands
with boughs of trees, or any light litter, a more abundant crop is produced. The
subject has been discussed in the journals of the Royal Agricultural Society. May
not the apparent increase be due entirely to the succulent condition in which a
plant always grows in the shade?
[58] This paper of Melloni’s will be found in the Bibliothèque Universelle de
Genève, for 1843. The conclusions are highly ingenious, but they rest entirely on
the analogy supposed to be discovered between the relations of heat, like light,
to the coloured rays of the spectrum. This, it must be remembered, is not the
case, since even Sir William Herschel showed that red light might exist with
only a minimum of calorific power, notwithstanding the fact, that the maximum
heat-ray of the spectrum coincides with the red rays.
[59] Dr. Robinson, of Armagh, in his Memoir On the Effects of Heat in lessening
the Affinities of the Elements of Water.—Transactions of the Royal Irish
Academy, vol. xxi. part 2.
[60] On this subject consult Robert Were Fox, On the Temperature of the Mines
of Cornwall.—Cornwall Geological Transactions, vol. ii.; W. J. Henwood, on the
same subject, Ib. vol. v.; Reports of the British Association, 1840, p. 315;
Edinburgh New Philosophical Journal, vol. xxiv. p. 140.
[61] On the causes of the temperature of Hot and Thermal Springs; and on the
bearings of this subject as connected with the general question regarding the
internal temperature of the Earth: by Professor Gustav Bischoff, of Bonn.—
Edinburgh New Philosophical Journal, vol. xx. p. 376; vol. xxiii. p. 330. Some
interesting information on the temperature of the ground will be found in
Erman’s Travels in Siberia, translated by W. D. Cooley, vol. i. p. 339; vol. ii. p.
366. Sur la Profondeur à laquelle se trouve la couche de Température invariable
entre les Tropiques, by Boussingault: Annales de Chimie et de Physique, 1833,
p. 225. Reference may also be made to Humboldt’s Cosmos, Otto’s translation;
and to the excellent article on Meteorology, by George Harvey, in the

Encyclopædia Metropolitana. These chthonisothermal lines, as they are called,
have been traced by Humboldt and others over extensive districts.
[62] These results are obtained from the valuable observations of Robert Were
Fox, Esq., made with great care by that gentleman in several of the Cornish
mines: Report on some observations on Subterranean Temperature.—British
Association Reports, vol. ix. p. 309; Philosophical Magazine, 1837, vol. ii. p.
520.
[63] From his experiments, the following conclusions were arrived at by M.
Delaroche:—
1. Invisible radiant heat may, in some circumstances, pass directly through glass.
2. The quantity of radiant heat which passes directly through glass is so much
greater, relative to the whole heat emitted in the same direction, as the
temperature of the source of heat is more elevated.
3. The calorific rays which have already passed through a screen of glass,
experience, in passing through a second glass screen of a similar nature, a much
smaller diminution of their intensity than they did in passing through the first
screen.
4. The rays emitted by a hot body differ from each other in their faculty to pass
through glass.
5. A thick glass, though as much or more permeable to light than a thin glass of
worse quality, allows a much smaller quantity of radiant heat to pass. The
difference is so much the less as the temperature of the radiating source is more
elevated.
6. The quantity of heat which a hot body yields in a given time, by radiation to a
cold body situate at a distance, increases, cæteris paribus, in a greater ratio than
the excess of temperature of the first body above the second.—Journal de
Physique, vol. lxxv.
[64] Sir David Brewster differs from the conclusions arrived at by Delaroche. He
thus explains his views:—“The inability of radiant heat to pass through glass,
may be considered as a consequence of its refusing to yield to the refractive
force; for we can scarcely conceive a particle of radiant matter freely permeating
a solid body, without suffering some change in its velocity and direction. The
ingenious experiments of M. Prévost, of Geneva, and the more recent ones of M.
Delaroche, have been considered as establishing the permeability of glass to
radiant heat. M. Prévost employed moveable screens of glass, and renewed them
continually, in order that the result which he obtained might not be ascribed to
the heating of the screen; but such is the rapidity with which heat is propagated
through a thin plate of glass, that it is extremely difficult, if not impossible, to
observe the state of the thermometer before it has been affected by the secondary
radiation from the screen. The method employed by M. Delaroche, of observing
the difference of effect, when a blackened glass screen and a transparent one
were made successively to intercept the radiant heat, is liable to an obvious error.
The radiant heat would find a quicker passage through the transparent screen;
and, therefore, the difference of effect was not due to the transmitted heat, but to
the heat radiated from the anterior surface. The truth contained in M.
Delaroche’s fifth proposition is almost a demonstration of the fallacy of all those

that precede it. He found that ‘a thick plate of glass, though as much or more
permeable to light than a thin glass of worse quality, allowed a much smaller
quantity of radiant heat to pass.’ If he had employed very thick plates of the
purest flint glass, or thick masses of fluid that have the power of transmitting
light copiously, he would have found that not a single particle of heat was
capable of passing directly through transparent media.”—Sir D. Brewster, On
new properties of heat as exhibited in its propagation along plates of glass.
Philosophical Transactions, vol. cvi. p. 107.
[65] Proposal of a New Nomenclature for the Science of Calorific Radiations, by
M. Melloni. Bibliothèque Universelle de Genève, No. 70. Scientific Memoirs,
vol. iii. part 12. Many of the terms, as Diathermasy, or transparency for heat;
Adiathermasy, opacity for heat; Thermochroic, coloured for heat, and others, are
valuable suggestions of forms of expression which are required in dealing with
these physical phenomena.
[66] For a careful examination of the several theories of heat consult Dr. Young’s
Course of Lectures on Natural Philosophy, &c., Lecture 52, On the Measures
and the Nature of Heat; also Powell’s very excellent Reports on Radiant Heat—
Reports of the British Association, 1832, 1840. The transcendental view which
the immaterial theory leads to, cannot be better exemplified than by the
following quotation from that inexplicable dream of a talented man, Elements of
Physiophilosophy, by Lorenz Oken, M.D. (translated for the Ray Society, by
Alfred Tulk):—
“Heat is not matter itself any more than light is; but it is only the act of motion in
the primary matter. In heat, as well as in light, there certainly resides a material
substratum; yet, this substratum does not give out heat and light; but the motion
only of the substratum gives out heat, and the tension only of the substratum
light. There is no body of heat; nitrogen is the body of heat, just as oxygen may
be called the body of fire. Heat is real space; into it all forms have been resolved,
as all materiality has been resolved into gravity, and all activity, all polarity, into
light. Heat is the universal form, consequently the want of form.”
[67] Mémoires de la Société Physique, &c., de Genève, tom. ii. art. 2.
[68] This curious phenomenon was first observed by Mr. Trevelyan, whose
Notice regarding some Experiments on the Vibration of Heated Metals will be
found in the Transactions of the Royal Society of Edinburgh, vol. xii., 1837. In a
Memoir in the same volume, entitled Experimental Researches regarding certain
vibrations which take place between metallic masses having different
temperatures, Professor Forbes draws the following conclusions:—
1. “The vibrations never take place between substances of the same nature.
2. “Both substances must be metallic. (This is now proved not to be necessary.)
3. “The vibrations take place with an intensity proportional (within certain
limits) to the difference of the conducting powers of the metals for heat or
electricity; the metal having the least conducting power being necessarily the
coldest.
4. “The time of contact of two points of the metals must be longer than that of
the intermediate portions.

5. “The impulse is received by a distinct and separate process at each contact of
the bar and block, and in no case is the metallic connection of the bearing points
in the bar, or those of the block, in any way essential.
6. “The intensity of the vibration is (under certain exceptions) proportional to the
difference of temperature of the metals.”—Transactions of the Royal Society of
Edinburgh, vol. xii.
[69] The Bakerian Lecture. On certain Phenomena of Voltaic Ignition, and the
Decomposition of Water into its Constituent Gases by Heat: by W. R. Grove,
Esq.—Philosophical Transactions, 1847. Part 1.
[70] Davy’s Researches on Flame. Works, vol. vi.—Philosophical Transactions
for 1817.
[71] On the Effect of Heat in lessening the affinities of the Elements of Water: by
the Rev. Thomas Romney Robinson, D.D.—Transactions of the Royal Irish
Academy, vol. xxi. part 2.
[72] An Inquiry concerning the Chemical Properties that have been attributed to
Light: by Benjamin, Count of Rumford.—Philosophical Transactions, vol.
lxxxviii. p. 449.—The results obtained by Count Rumford were probably due to
the non-luminous heat-rays—parathermic rays—which are known to be given
off by boiling water.
[73] For Dr. Drapers paper, see Philosophical Magazine for May, 1847, vol. xxx.
3rd series.
[74] On the Action of the Rays of the Solar Spectrum on Vegetable Colours: by
Sir J. F. W. Herschel, Bart.
The proof of the continuation of the visible prismatic spectrum beyond the
extreme violet may be witnessed in the following manner:—“Paper stained with
tincture of turmeric is of a yellow colour; and, in consequence, the spectrum
thrown in it, if exposed in open daylight, is considerably affected in its apparent
colours, the blue portion appearing violet, and the violet very pale and faint; but
beyond the region occupied by the violet rays, is distinctly to be seen a faint
prolongation of the spectrum, terminated laterally, like the rest of it, by straight
and sharp outlines, and which, in this case, affects the eye with the sensation of a
pale yellow colour.”—Philosophical Transactions, p. 133.
[75] The most complete exposition of the theory that animal heat is derived from
chemical action only, will be found in Animal Chemistry, or Chemistry in its
applications to Physiology and Pathology, by Justus Liebig: translated by Dr.
Gregory. The conclusions arrived at by the author, notwithstanding his high—
and deservedly high—position in chemical science, must, however, be received
with great caution, many of them being founded on most incorrect premises, and
his generalizations being of the most hasty and imperfect character. At page 22
the following passage occurs:—“If we were to go naked, like certain savage
tribes, or if in hunting or fishing we were exposed to the same degree of cold as
the Samoiedes, we should be able, with ease, to consume ten pounds of flesh,
and, perhaps, a dozen of tallow candles into the bargain, daily, as warmly clad
travellers have related with astonishment of these people. We should then also be
able to take the same quantity of brandy or train-oil without bad effects, because

the carbon and hydrogen of these substances would only suffice to keep up the
equilibrium between the external temperature and that of our bodies.”
A brief examination will exhibit the error of this. The analysis of Beef, by D.
Lyon Playfair, is as follows:—
Carbon 51·83
Hydrogen 7·57
Nitrogen 15·01
Oxygen 21·37
Ashes 4·23
And the following has been given by Chevreul as the composition of mutton
tallow:—
Carbon 96
Hydrogen 16
Nitrogen 16
Oxygen 48
About three times the quantity of oxygen to the carbon eaten, is required to
convert it into carbonic acid; hence, the Samoiede, eating more highly
carbonized matter, must inspire 288 oz. of oxygen daily, or nearly eight times as
much as the “ordinary adult.” By the lungs he must take into the body 2,304
cubic feet of air besides what will be absorbed by the skin. His respirations must
be so much quickened, that at the lowest possible calculation he must have 500
pulsations a minute. Under such conditions it is quite clear man could not exist.
There is no disputing the fact of the enormous appetites of these people; but all
the food is not removed from the system as carbonic acid gas.
[76] An interesting paper by Dr. Davy, On the Temperature of Man, will be
found in the Philosophical Transactions, vol. cxxxvi. p. 319.—Sir Humphry
Davy, in his Consolations in Travel, or the Last Days of a Philosopher, in his
fourth dialogue, The Proteus, has several ingenious speculations on this subject.
[77] Exposé de quelques résultats obtenus par l’action combinée de la chaleur et
de la compression sur certains liquides, tels que l’eau, l’alcool, l’éther
sulfurique, et l’essence de pétrole rectifiée: par M. le Baron Cagniard de la Tour.
The three following conclusions are arrived at:—
1. Que l’alcool à 36 degrés, l’essence de pétrole rectifiée à 42 degrés, et l’éther
sulfurique soumis à l’action de la chaleur et de la compression, sont susceptibles
de se réduire complètement en vapeur sous un volume un peu plus que double de
celui de chaque liquide.
2. Qu’une augmentation de pression, occasionnée par la présence de l’air dans
plusieurs des experiences qui viennent d’être citées, n’a point apporté d’obstacle
à l’évaporation du liquide dans le même espace; qu’elle a seulement rendu sa
dilatation plus calme et plus facile à suivre jusqu’au moment où le liquide
semble s’évanouir tout-à-coup.
3. Que l’eau, quoique susceptible sans doute d’être réduite en vapeur très-
comprimée, n’a pu être soumise à des experiences complètes, faute de moyens

suffisans pour assurer l’exacte fermeture de la marmite de compression, non plus
que dans les tubes de verre dont elle altère la transparence en s’emparant de
l’alcali qui entre dans leur composition.—Annales de Chimie, vol. xxi.
[78] Sur les phénomènes qui présentent les corps projetés sur des surfaces
chaudes: par M. Boutigny (d’Evreux).—Annales de Chimie et de Physique, vol.
xi. p. 16. Congélation du mercure en trois secondes, en vertu de l’état sphéroïdal
dans un creuset incandescent: by M. Faraday.—Ibid., vol. xix. p. 383.
Spheroidal Condition of Bodies (Extrait d’une Note de M. Boutigny d’Evreux).
“Au nombre des propriétés des corps à l’état sphéroïdal, il en est cinq qui me
paraissent caractéristiques et fondamentales, et c’est sur ces cinq propriétés que
je base la définition que je soumets aujourd’hui au jugement de l’Académie. Ces
cinq propriétés sont:—
“1. La forme arrondie que prend la matière sur une surface chauffée à une
certaine température.
“2. Le fait de la distance permanente qui existe entre le corps à l’état sphéroïdal
et le corps sphéroïdalisant.
“3. La propriété de réfléchir le calorique rayonnant.
“4. La suspension de l’action chimique.
“5. La fixité de la température des corps à l’état sphéroïdal.
“Cela posé, voici la définition que je propose: un corps projeté sur une surface
chaude est à l’état sphéroïdal quand il revêt la forme arrondie et qu’il se
maintient sur cette surface au delà du rayon de sa sphère d’activité physique et
chimique; alors il réfléchit le calorique rayonnant, et ses molécules sont, quant à
la chaleur, dans un état d’équilibre stable; c’est-à-dire, à une température
invariable, ou qui ne varie que dans des limites étroites.”—Comptes Rendus, 6
Mars, 1848.
[79] Some Facts relative to the Spheroidal State of Bodies, Fire Ordeal,
Incombustible Man, &c.: by P. H. Boutigny (d’Evreux), Philosophical Magazine,
No. 233 (third, series), p. 80; Comptes Rendus, May 14, 1849.
[80] The theory of freezing mixtures is deduced from the doctrine of latent
caloric. These are mixtures of saline substances which, at the common
temperature, by their mutual chemical action, pass rapidly into the fluid form, or
are capable of being rapidly dissolved in water, and, by this quick transition to
fluidity, absorb caloric, and produce degrees of cold more or less intense.—Rev.
Francis Lunn, On Heat: Encyclopædia Metropolitana.
[81] Propriétés de l’Acide Carbonique liquide, par M. Thilorier, Annales de
Chimie, vol. lx. p. 427. Solidification de l’Acide Carbonique: Ibid. p. 432.
[82] On the Liquefaction and Solidification of Bodies generally existing as
Gases, by Michael Faraday, D.C.L., F.R.S., &c.; Philosophical Transactions, vol.
cxxxvi, p. 155.
[83] Burns, in one of his most natural and pathetic letters.

CHAPTER VII.
LIGHT.
Theories of the Nature of Light—Hypotheses of Newton and
Huygens—Sources of Light—The Sun—Velocity of Light—
Transparency—Dark Lines of the Spectrum—Absorption of
Light—Colour—Prismatic Analysis—Rays of the Spectrum
—Rainbow—Diffraction—Interference—Goethe’s Theory
—Polarisation—Magnetisation of Light—Vision—The Eye
—Analogy—Sound and Light—Influence of Light on
Animals and Vegetables—Phosphorescence arising from
several Causes—Artificial Light—Its Colour dependent on
Matter.

Light, the first creation, presents to the enquiring mind a series of
phenomena of the most exalted character. The glowing sunshine, painting
the earth with all the brilliancy of colour, and giving to the landscape the
inimitable charm of every degree of illumination, from the grey shadow to
the golden glow;—the calm of evening, when, weary of the “excess of
splendour,” the eye can repose in tranquillity upon the “cloud-land” of the
west, and watch the golden and the ruddy hues fade slowly into the blue
tincture of night;—and the pale refulgence of the moon, with the quiet
sparkle of the sun-lit stars,—all tend to impress upon the soul, the great
truth that, where there is light, organisation and life are found, and beyond
its influence death and silence hold supreme dominion.[84] Through all time
we have evidences that this has been the prevailing feeling of the human
race, derived, of course, from their observation of the natural phenomena
dependent upon luminous agency. In the myths of every country,
impersonations of light prevail, and to these are referred the mysteries of
the perpetual renewal of life on the surface of the earth.
This presentiment of a philosophic truth, in the instance of the poet sages of
intellectual Greece, was advanced to the highest degree of refinement; and

the sublime exclamation of Plato: “Light is truth, and God is light,”
approaches nearly to a divine revelation.
As the medium of vision—as the cause of colour—as a power influencing
in a most striking manner all the forms of organisation around us, light
presented to the inquiring minds of all ages a subject of the highest interest.
The ancient philosophers, although they lost themselves in the metaphysical
subtleties of their schools, could not but discover in light an element of the
utmost importance in natural operations. The alchemists regarded the
luminous principle as a most subtile fluid, capable of interpenetrating and
mingling with gross matter: gold being supposed to differ from the baser
metals only in containing a larger quantity of this ethereal essence.[85]
Modern science, after investigating most attentively a greater number of the
phenomena of light, has endeavoured to assist the inquiry by the aid of
hypotheses. Newton, in a theory, which exhibits the refined character of that
great philosopher’s mind, supposes luminous particles to dart from the
surfaces of bodies in all directions—that these infinitely minute particles
are influenced by the attracting and repelling forces of matter, and thus
turned back, or reflected, from their superficies in some cases, and absorbed
into their interstitial spaces in others.
Huyghens, on the contrary, supposes light to be caused by the waves or
vibrations of an infinitely elastic medium—Ether—diffused through all
space, which waves are propagated in every direction from the luminous
body. In the first theory, a luminous particle is supposed actually to come
from the sun to the earth; in the other, the sun only occasions a disturbance
of the ether, which extends with great rapidity, in the same manner as a
wave spreads itself over the surface of a lake.
Nearly all the facts known in the time of Newton, and those discovered by
him, were explained most satisfactorily by his hypothesis; but it was found
they could be interpreted equally as the effects of undulation, with the
exception of the production of colour by prismatic refraction. Although the
labours of many gifted minds have been given, with the utmost devotion, to
the support of the vibratory theory, this simple fact has never yet received
any satisfactory explanation; and there are numerous discoveries connected
with the molecular and chemical disturbances produced by the sun’s rays,

which do not appear to be explained by the hypothesis of emission or of
undulation.
In both theories a wave motion is admitted, and every fact renders it
probable that this mode of progression applies not only to light, but to the
so-called imponderable forces in general. Admitting, therefore, the
undulatory movement of luminous rays, we shall not stop to consider those
points of the discussion which have been so ably dealt with by Young,
Laplace, Fresnel, Biot, Fraunhofer, Herschel, Brewster, and others, but
proceed at once to consider the sources of light, and its more remarkable
phenomena.[86]
The sun is the greatest permanently luminous body we are acquainted with,
and that orb is continually pouring off light from its surface in all directions
at the rate, through the resisting medium of space and of our own
atmosphere, of 192,000 miles in a second of time. It has been calculated,
however, that light would move through a vacuum with the speed of
192,500 miles in the same period. We, therefore, learn that a ray of light
requires eight minutes and thirteen seconds to come from the sun to us. In
travelling from the distant planet Uranus, nearly three hours are exhausted;
and from the nearest of the fixed stars each ray of light requires more than
six years to traverse the intervening space between it and the earth. Allow
the mind to advance to the regions of nebulæ, and it will be found that
hundreds of years must glide away during the passage of their radiations.
Consequently, if one of those masses of matter, or even one of the remote
fixed stars, was “blotted out of heaven” to-day, several generations of the
finite inhabitants of this world would fade out of time before the
obliteration could be known to man. Here the immensity of space assists us
in our conception, limited though it be, of the for-ever of eternity.[87]
All the planets of our system shine with reflected light, and the moon, our
satellite, also owes her silvery lustre to the sun’s radiations. The fixed stars
are, in all probability, suns shining from the far distance of space, with their
own self-emitted lights. By the photometric researches of Dr. Wollaston, we
learn, however, that it would take 20,000 millions of such orbs as Sirius, the
brightest of the fixed stars, to afford as much light as we derive from the
sun. The same observer has proved that the brightest effulgence of the full
moon is yet 801,072 times less than the luminous power of our solar centre.

The cultivators of modern science are a bold race; not contented with
endeavouring to understand the physical earth, they are endeavouring to
comprehend the condition of the solar surface. The mind of man can
penetrate far into nature, and, as it were, feel out the mysteries of
untraversed space. The astronomer learns of a peculiar condition of light,
which is termed polarisation, and he learns by this, too, that he can
determine if from a bright luminous disc the light is derived from a solid
mass in a state of intense ignition, or from vapour in an incandescent
condition. He adds a polarising apparatus to his telescopes, and he
determines that the light we derive from the sun is due to an envelope of
vapour—burning, in all probability—only with greater intensity, as the gas
which we now employ. This Photosphere—as it has been called by the late
French philosopher Arago, is found to be subjected to violent disturbances,
and the dark spots seen on the sun’s disc are now known to be openings
through this mysterious envelope of light, which enable us to look in upon
the dark body of the sun itself.
Luminous phenomena may be produced by various means—chemical
action is a source of light; and, under several circumstances in which the
laws of affinity are strongly exerted, a very intense luminous effect is
produced. Under this head all the phenomena of combustion are included.
In the electric spark we have the development of light; and the arc which is
formed between charcoal points at the poles of a powerful voltaic battery
affords us the most intense artificial illumination with which we are
acquainted. In addition to these, we have the peculiar phenomena of
phosphorescence arising from chemical, calorific, electrical, actinic, and
vital excitation, all of which must be particularly examined.
From whatever source we procure light, it is the same in character, differing
only in intensity. In its action upon matter, we have the phenomena of
transmission, of reflection, of refraction, of colour, of polarisation, and of
vision, to engage our attention.
A beam of white light falls upon a plate of colourless glass, and it passes
freely through it, losing but little of its intensity; the largest portion being
lost by reflection from the first surface upon which the light impinges. If the
glass is roughened by grinding, we lose more light by absorption and by
reflection from the asperities of the roughened surface; but if we cover that
face with any oleaginous fluid, as, for instance, turpentine, its transparency

is restored. We have thus direct proof that transparency to light is due to
molecular condition. This may be most strikingly shown by an interesting
experiment of Sir David Brewster’s:—
If a glass tube is filled with nitrous acid vapour, which is of a dull red
colour, it admits freely the passage of the red and orange rays with some of
the others, and, if held upright in the sunshine, casts a red shadow on the
ground; by gently warming it with a spirit-lamp, whilst in this position, it
acquires a much deeper and blacker colour, and becomes almost impervious
to any of the rays of light; but upon cooling it again recovers its
transparency.
It has also been stated by the same exact experimentalist, that having
brought a purple glass to a red heat, its transparency was improved, so that
it transmitted green, yellow, and red rays, which it previously absorbed; but
the glass recovered its absorptive powers as it cooled. A piece of yellowish-
green glass lost its transparency almost entirely by being heated. Native
yellow orpiment becomes blood-red upon being warmed, when nearly all
but the red rays are absorbed; and pure phosphorus, which is of a pale
yellow colour, and transmits freely all the coloured rays upon being melted,
becomes very dark, and transmits no light.
Chemistry affords numerous examples of a very slight change of condition,
producing absolute opacity in fluids which were previously diaphanous.[88]
Charcoal absorbs all the light which falls upon it, but in some of its states of
combination, and in the diamond, which is pure carbon, it is highly
transparent. Gold and silver beaten into thin leaves are permeated by the
green and blue rays, and the metals in combination with acids are all of
them more or less transparent. What becomes of the light which falls upon
and is absorbed by bodies, is a question which we cannot yet,
notwithstanding the extensive observations that have been made by some of
the most gifted of men, answer satisfactorily. In all probability, as already
stated, it is permanently retained within their substances; and many of the
experiments of exciting light in bodies when in perfect darkness, by the
electric spark and other means, appear to support the idea of light becoming
latent or hidden.
No body is absolutely transparent; some light is lost in passing even
through ethereal space, and still more in traversing our atmosphere.

Amongst the most curious instances of absorption is that which is uniformly
discovered in the solar spectrum, particularly when we examine it with a
telescope. We then find that the coloured rays are crossed by a great number
of dark bands or lines, giving no light; these are generally called
Fraunhofer’s dark lines, as it was to the indefatigable exertions of that
experimentalist, and by the aid of his beautiful instruments, that most of
them were discovered and measured, and enumerated, although they were
previously noticed by Dr. Wollaston. It is quite clear that those lines
represent rays which have been absorbed in their passage from the sun to
the earth: although some of them have no doubt undergone absorption
within the limits of the earth’s atmosphere, we have every reason to believe,
with Sir John Herschel, that the principal absorption takes place in the
atmosphere of the sun.[89]
It has been proved by Dr. Miller, that the number of those dark lines is
continually varying with the alteration of atmospheric conditions;[90] and
the evidences which have been afforded, of peculiar states of absorption by
the gaseous envelope of the earth,—during the prosecution of investigations
on the chemical agencies of the sun’s rays,—are of a sufficiently convincing
character.
It has been calculated by Bouguer, that if our atmosphere, in its purest state,
could be extended rather more than 700 miles from the earth’s surface
instead of nearly 40, as it is at present, the sun’s rays could not penetrate it,
and this globe would roll on in darkness and silence, without a vestige of
vegetable form or of animal life. In the Hebrew version of the Mosaic
History, the reading is, “Let light appear:” may not this really mean that the
earth’s atmosphere was so cleared of obstructing vapours, that the solar rays
were enabled to reach the earth? The same calculation supposes that sea-
water loses all its transparency at the depth of 730 feet; but a dim twilight
must prevail much deeper in the ocean.
The researches of Professor Edward Forbes have proved, that at the depth
of 230 fathoms in the Ægean sea, the few shelled animals that exist are
colourless: no plants are found within that zone; and that industrious
naturalist fixes the zero of animal life of those waters at about 300 fathoms.
[91]
Since these zones mark the rapidly diminishing light, it is evident that

where life ceases to be must be beyond the limits to which life can
penetrate.
Our atmosphere, charged with aqueous vapour, serves to shield us from the
intense action of the solar powers. By it we are protected from the
destructive influences of the sun’s light and heat; enjoy those modified
conditions which are most conducive to the healthful being of organic
forms; to it we owe “the blue sky bending over all,” and those beauties of
morning and evening twilight of which

—— Sound and motion own the potent sway.
Responding to the charm with its own mystery.

To defective transparency, or rather to the different degrees of it, we must
attribute, in part, the colours of permeable media. Thus, a glass or fluid
appears yellow to the eye, because it has the property of admitting the
permeation of a larger quantity of the yellow rays than of any others;—red,
because the red rays pass it with the greatest freedom; and so on for every
other colour. In most cases the powers of transmission and of reflection are
similar; but it is not so in all; a variety of fluor spar, which, while it
transmits green light, reflects blue, and the precious opal, are striking
instances to the contrary. Some glasses, which transmit yellow light have
the singular power of dispersing blue rays from one surface; and a solution
of quinine in water acidulated with sulphuric acid, although perfectly
transparent and colourless when held between the eye and the light,
exhibits, if viewed in a particular direction, a lively cerulean tint. These
effects being supposed to be due to the conditions of the surface, have been
called epipolic phenomena.[92]
The careful investigation of these phenomena has made us acquainted with
some very interesting facts, and indeed discovered to us a set of luminous
rays which were previously unknown. The dispersion of blue light from the
surface of some yellow glasses—such as have been coloured by the oxide
of silver—is of a different order from that which takes place with the
solution of sulphate of quinine, or with the fluor spar. The first depends
upon a peculiar condition of the surface, while the latter phenomena are due
to a dispersion which takes place within the solid or fluid. In addition to the

sulphate of quinine, and the fluor spar, we obtain the same results in a very
marked manner by a canary yellow glass, coloured with the oxide of
uranium, and by a decoction of the inner bark of the horse-chesnut tree. Mr.
Stokes, who has investigated this class of phenomena, and proposes to call
it Fluorescence, from its being naturally seen in fluor-spar, has shown that
the peculiar internal dispersion, and the consequent alteration of the colour
of the ray, is due to an alteration in its refrangibility. Whether this
hypothesis prove to be the correct one or not, it is certain that there exists a
set of rays of far higher refrangibility than those seen in the ordinary
Newtonian spectrum. This may be shown in the following manner: taking
either of the solutions named, or a block of uranium glass, throw upon one
face, by means of a prism, a very pure spectrum. On looking into the glass
or fluid there will be seen, commencing amidst the most refrangible rays, a
new set of spectral rays, struggling to make their way through the absorbent
medium. These are of a blue colour in the quinine or chesnut solution, and
green in the uranium glass, and are seen extending themselves far beyond
the most refrangible rays of the ordinary Newtonian spectrum. This is the
space over which those rays which have the power of producing chemical
changes, such as are rendered familiar by the practice of Photography, are
detected in their greatest activity. It has, therefore, been supposed that these
fluorescent rays are the chemical rays rendered luminous by the alteration
of their refrangibility. This view has received much support from the fact
that the extra spectral rays are crossed with numerous dark lines, and that in
the chemical impressions these lines are marked by unchanged spaces
which exactly coincide with them. There is, however, much doubt of the
correctness of this, since, in the uranium glass of such a thickness that these
visible rays are quite absorbed, the chemical rays still pass.
However, the whole question requires, and is receiving, the most searching
investigation. The discovery of these phenomena, which are included under
the term of Fluorescence, is of that interesting and important character, that
it must be ranked as the most decided advance which has been made in
physical optics since the days of Newton.
It is not improbable that those rays of such high refrangibility may, although
they are under ordinary circumstances invisible to the human eye, be
adapted to produce the necessary degree of excitement upon which vision
depends in the optic nerves of the night-roaming animals. The bat, the owl,

and the cat, may see in the gloom of night by the aid of rays which are
invisible to, or inactive on the eyes of man, or of those animals which
require the light of day for perfect vision.
It is a general law of the radiant forces, that whenever they fall upon any
surface, a portion is thrown back or reflected at the same time as other
portions are absorbed or transmitted. Upon this peculiarity appear to depend
the phenomena of natural colour in bodies.
The white light of the sun is well known to be composed of several
coloured rays. Or rather, according to the theory of undulations, when the
rate at which a ray vibrates is altered, a different sensation is produced upon
the optic nerve. The analytical examination of this question shows, that to
produce a red colour the ray of light must give 37,640 undulations in an
inch, and 458,000000,000000 in a second. Yellow light requires 44,000
undulations in an inch, and 535,000000,000000 in a second; whilst the
effect of blue results from 51,110 undulations within an inch, and
622,000000,000000 of waves in a second of time.[93] The determination of
such points as these is among the highest refinements of science, and, when
contrasted with the most sublime efforts of the imagination, they must
appear immeasurably superior.
If a body sends back white light unchanged, it appears white; if the surface
has the property of altering the vibration to that degree which is calculated
to produce redness, the result is a red colour: the annihilation of the
undulations produces blackness. By the other view, or the corpuscular
hypothesis, the beam of white light is supposed to consist of certain
coloured rays, each of which has physical properties peculiar to itself, and
thus is capable of producing different physiological effects. These rays
falling upon a transparent or an opaque body suffer more or less absorption,
and being thus dissevered, we have the effect of colour. A red body absorbs
all the rays but the red; a blue surface, all but the blue; a yellow, all but the
yellow; and a black surface absorbs the whole of the light which falls upon
it.
That natural colours are the result of white light, and not innate properties
of the bodies themselves, is most conclusively shown by placing coloured
bodies in monochromatic light of another kind, when they will appear either
of the colour of that light, or, by absorbing it, become black; whereas, when

placed in light of their own character, the intensity of colour is greatly
increasing.
Every surface has, therefore, a peculiar constitution, by which it gives rise
to the diversified hues of nature. The rich and lively green, which so
abundantly overspreads the surface of the earth, the varied colours of the
flowers, and the numberless tints of animals, together with all those of the
productions of the mineral kingdom, and of the artificial combinations of
chemical manufacture, result from powers by which the relations of matter
to light are rendered permanent, until its physical conditions undergo some
change.
There is a remarkable correspondence between the geographical position of
a region and the colours of its plants and animals. Within the tropics, where

“The sun shines for ever unchangeably bright,”

the darkest green prevails over the leaves of plants; the flowers and fruits
are tinctured with colours of the deepest dye, whilst the plumage of the
birds is of the most variegated description and of the richest hues. In the
people also of these climes there is manifested a desire for the most striking
colours, and their dresses have all a distinguishing character, not of shape
merely, but of chromatic arrangement. In the temperate climates everything
is of a more subdued variety: the flowers are less bright of hue; the
prevailing tint of the winged tribes is a russet brown; and the dresses of the
inhabitants of these regions are of a sombre character. In the colder portions
of the earth there is but little colour; the flowers are generally white or
yellow, and the animals exhibit no other contrast than that which white and
black afford. A chromatic scale might be formed, its maximum point being
at the equator, and its minimum at the poles.[94]
The influence of light on the colours of organized creation is well shown in
the sea. Near the shores we find sea-weeds of the most beautiful hues,
particularly on the rocks which are left dry by the tides; and the rich tints of
the actiniæ, which inhabit shallow water, must have been often observed.
The fishes which swim near the surface are also distinguished by the variety
of their colours, whereas those which live at greater depths are grey, brown,
or black. It has been found that after a certain depth, where the quantity of

light is so reduced that a mere twilight prevails, the inhabitants of the ocean
become nearly colourless. That the sun’s ray alone gives to plants the
property of reflecting colour is proved by the process of blanching, or
etiolation, produced by artificially excluding the light.
By a triangular piece of glass—a prism,—we are enabled to resolve light
into its ultimate rays. The white pencil of light which falls on the first
surface of the prism is bent from its path, and coloured bands of different
colours are obtained. These bands or rays observe a curious constancy in
their positions: the red ray is always the least bent out of the straight path:
the yellow class comes next in the order of refrangibility; and the blue are
the most diverted from the vertex of the prism. The largest amount of
illuminating power exists in the yellow ray, and it diminishes towards either
end.[95] It is not uninteresting to observe something like the same variety of
colour occurring at each end of the prismatic spectrum. The strict order in
which the pure and mixed coloured rays present themselves is as follows:—
1. The extreme red: a ray which can only be discovered when the eye is
protected from the glare of the other rays by a cobalt blue glass, is of a
crimson character—a mixture of the red and the blue, red predominating.
[96]

2. The red: the first ray visible under ordinary circumstances.
3. The orange: red passing into and combining with yellow.
4. The yellow: the most intensely luminous of the rays.
5. The green: the yellow passing into and blending with the blue.
6. The blue: in which the light very rapidly diminishes.
7. The indigo: the dark intensity of blue.
8. The violet: the blue mingled again with the red—blue being in excess.
9. The lavender grey: a neutral tint, produced by the combination of the red,
blue, and yellow rays, which is discovered most easily when the spectrum is
thrown upon a sheet of turmeric paper.
10. The fluorescent rays: which are either a pure silvery blue or a delicate
green.

Newton regarded the spectrum as consisting of seven colours of definite
and unvarying refrangibility. Brewster and others appear to have detected a
great diffusion of the colours over the spectrum, and regard white light as
consisting only of three rays, which in the prismatic images overlap each
other; and from these—red, yellow, and blue—all the others can be formed
by combination in varying proportions. The truth will probably be found to
be, that the ordinary prismatic spectrum is a compound of two spectra:—
that is, as we have the ordinary rainbow, and a supplementary bow, the
colours of which are inverted, so the extraordinary may be somewhat
masked by the intense light of the ordinary spectrum; and yet by
overlapping produce the variations of colour in the rays. We have already
examined the heating power found in these coloured bands, which, although
shown to be in a remarkable manner in constant agreement with the colour
of a particular ray, is not directly connected with it; that is, not as the effect
of a cause, or the contrary. The chemical action of the solar rays, to which
from its important bearings we shall devote a separate chapter, has, in like
manner with heat, been confounded with the sun’s luminous power; but
although associated with light and heat, and modified by their presence, it
must be distinguished from them.
We find the maximum of heat at one end of the spectrum, and that of
chemical excitation at the other—luminous power observing a mean point
between them. Without doubt we have these powers acting reciprocally,
modifying all the phenomena of each other, and thus giving rise to the
difficulties which beset the inquirer on every side.
We have beautiful natural illustrations of luminous refraction in the rainbow
and in the halo: in both cases the rays of light being separated by the
refractive power of the falling rain drop, or the vesicles which form the
moisture constituting a fog. In the simple toy of the child—the soap-bubble
floating upon the air—the philosopher finds subjects for his contemplation;
and from the unrivalled play of colours which he discovers in that
attenuated film, he learns that the varying thicknesses of surfaces influence,
in a most remarkable manner, the colours of the sunbeam. Films of oil
floating upon water present similar appearances; and the colours developed
in tempering steel are due entirely to the thickness of the oxidized surface
produced by heat. There have lately been introduced some beautiful
specimens of paper rendered richly iridescent by the following process:—A

solution of a gum resin in chloroform is floated upon water, where it forms
a film giving all the colours of Newton’s rings. A sheet of paper which has
been previously sunk in the water is carefully lifted, and the film thus
removed adheres with great firmness to the paper, and produces this rich
and curious play of colour. The rich tints upon mother-of-pearl, in the
feathers of many birds, the rings seen in the cracks of rock-crystal, or
between the unequal faces of two pieces of glass, and produced by many
chemical and indeed mechanical operations—are all owing to the same
cause;—the refraction of the luminous pencil by the condition of the film or
surface. If we take one of those steel ornaments which are formed by being
covered with an immense number of fine lines, it will be evident that these
striæ present many different angles of reflection, and that, consequently, the
rays thrown back will, at some point or another, have a tendency to cross
each other. The result of this is, that the quantity of light is augmented at
some points of intersection, and annihilated at others.[97] Out of the
investigation of the phenomena of diffraction, of the effects of thin and
thick plates upon light, and the results of interference, has arisen the
discovery of one of the most remarkable conditions within the range of
physical science.
Two bright lights may be made to produce darkness.—If two pencils of
light radiate from two spots very close to each other in such a manner that
they cross each other at a given point, any object placed at that line of
interference will be illuminated with the sum of the two luminous pencils. If
we suppose those rays to move in waves, and the elevation of the wave to
represent the maximum of luminous effect, then the two waves meeting,
when they are both at the height of their undulation, will necessarily
produce a spot of greater intensity. If now we so arrange the points of
radiation, that the systems of luminous waves proceed irregularly, and that
one arrives at the screen half an undulation before the other, the one in
elevation falling into the depression of the other, a mutual annihilation is
the consequence. This fact, paradoxical as it may appear, was broadly stated
by Grimaldi, in the description of his experiments on the inflection of light,
and has been observed by many others. The vibratory hypothesis, seizing
upon the analogy presented by two systems of waves in water, explains this
plausibly, and many similar phenomena of what is called the interference of

light; but still upon examination it does not appear that the explanation is
quite free from objection.[98]
Another theory, not altogether new to us, it being indicated in Mayer’s
hypothesis of three primary colours (1775), and to be found as a problem in
some of the Encyclopædias of the last century, has been put forth, in a very
original manner, by that master-mind of intellectual Germany, Goethe; and
from the very comprehensive views which this poet-philosopher has taken
of both animal and vegetable physiology (views which have been adopted
by some of the first naturalists of Europe), we are bound to receive his
theory of colours with every respect and attention.
Goethe regards colour as the “thinning” of light; for example, by
obstructing a portion of white light, yellow is produced; by reducing it still
farther, red is supposed to result; and by yet farther retarding the free
passage of the beam, we procure a blue colour, which is the next remove
from blackness, or the absence of light. There is truth in this; it bears about
it a simplicity which will satisfy many minds; by it many of the phenomena
of colour may be explained: but it is insufficient for any interpretation of
several of those laws to which the other theories do give us some insight.
Newton may have allowed himself to be misled by the analogy presented
between the seven rays of the spectrum and the notes in an octave. The
mystic number, seven, may have clung like a fibre of the web of
superstition to the cloak of the great philosopher; but the attack made by
Goethe upon the Newtonian philosophy betrays the melancholy fact of his
being diseased with the lamentable weakness of too many exalted minds—
an overweening self-esteem.
The polarization of light, as it has been unfortunately called—unfortunately,
as conveying an idea of determinate and different points or poles, which
only exists in hypothetical analogy—presents to us a class of phenomena
which promise to unclose the mysterious doors of the molecular
constitution of bodies.
This remarkable condition, as produced by the reflection of light from glass
at a particular angle, was first observed by Malus, in 1808,[99] when
amusing himself by looking at the beams of the setting sun, reflected from
the windows of the Luxembourg Palace through a double refracting prism.
He observed that when the prism was in one position, the windows with

their golden rays were visible; but that turned round a quarter of a circle
from that position, the reflected rays disappeared although the windows
were still seen.
The phenomenon of double refraction was noticed, in the first instance, by
Erasmus Bartholin, in Iceland-spar, a crystal the primary form of which is a
rhombohedron; who perceived that the two images produced by this body
were not in the same physical conditions.[100] It was also studied by
Huyghens and Sir Isaac Newton, and to our countryman we owe the
singular idea that a ray of light emerging from such a crystal has sides. This
breaking up of the beam of light into two,—which is shown by looking
through a pin-hole on a card through a crystal of Iceland spar, when two
holes become visible, is due to the different states of tension in which the
different layers constituting the crystal exist.
In thus separating the ray of light into two rays, the condition called
polarisation has been produced, and by experiment we discover that the
single ray has properties different from those of the compound or ordinary
ray.
It is somewhat difficult to explain what is meant by, and what are the
conditions of, polarised light. In the first instance let us see by what
methods this peculiar state may be brought about.
If we reflect a ray of light from the surface of any body, fluid or solid, but
not metallic, at an angle between 53° and 68° it undergoes what has been
called plane polarisation. It may also be produced by the refraction of light
from several refracting surfaces acting upon the pencil of light in
succession; as by a bundle of plates of glass. Each surface polarises a
portion of the pencil, and the number of plates necessary to polarise a whole
beam depends upon the intensity of the beam and the angle of incidence.
Thus, the light of a wax candle is wholly polarised by forty-seven plates of
glass at an angle of 40° 41'; while at an angle of 79° 11' it is polarised by
eight plates. Again, plane polarisation may be produced by the double
refraction of crystals. Each of the two pencils is polarised, like light
reflected from glass at an angle of 56° 45', but in opposite planes.
Non-scientific readers will still ask,—What is this mysterious condition of
light which is produced by reflection and refraction at peculiar angles to the

incident ray. It is one of the most difficult of problems to express in popular
language. The conditions are, however, these:—
An ordinary ray of light will be reflected from a reflecting surface at
whatever angle that surface may be placed in relation to the incident beam.
A polarised ray of light is not reflected in all positions of the reflecting
surface.
An ordinary ray of light is freely transmitted through a transparent medium,
as glass, in whatever position it may be placed relative to the source of
light.
A polarised ray of light is not transmitted in all the positions of the
permeable medium.
Supposing a plate of glass is presented at the angle 56° to a polarised ray,
and the plane of incidence or reflexion is at right angles to the plane of
polarisation of the ray, no light is reflected. If we turn the plate of glass
round through 90°, when the plane of reflexion is parallel to that of
polarisation the light is reflected. If we turn the plate round another 90°, so
that the plane of reflexion and of polarisation are parallel to each other,
again no light is reflected; and if we turn it through another 90° the
reflection of the ray again takes place.
Precisely the same result takes place when, instead of being reflected, the
polarised ray is transmitted.
Some substances have peculiar polarizing powers: the tourmaline is a
familiar example. If a slice of tourmaline is taken, and we look at a
common pencil of light through it, we see it in whatever position we may
place the transparent medium. If, however, we look at a pencil of polarised
light, and turn the crystal round, it will be found that in two positions the
light is stopped, and that in two other positions it passes freely through it to
the eye.
By way of endeavouring to conceive something of what may be the
conditions which determine this very mysterious state, let us suppose each
ray of light to vibrate in two planes at right angles to each other: one wave
being vertical and the other horizontal. We have many examples of this
compound motion. The mast of a ship, by the force with which she is urged
through the water, describes a vertical wave, while by the roll of the billows

across which she sails, a lateral undulation is produced at the same time. We
may sometimes observe the same thing when a field of corn is agitated by a
shifting wind on a gusty day.
The hypothesis therefore is, that every ray of ordinary light consists of two
rays vibrating in different planes; and that these rays, separated one from
the other, have the physical conditions which we call polarized.
The most transparent bodies may be regarded as being made up of atoms
arranged in certain planes. Suppose the plane of lamination of any
substance to be vertical in position, it would appear that the ray which has a
vertical motion passes it freely, whereas if we turn the body round so that
the planes of lamination are at right angles to the plane of vibration of the
ray, it cannot pass.
That some action similar to that which it is here endeavoured to express in
popular language does take place, is proved by the correctness of the results
deduced by rigid mathematical analyses founded on this hypothesis.
There are two other conditions of the polarization of light—called circular
and elliptical polarization. The first is produced by light when it is twice
reflected from the second surface of bodies at their angle of maximum
polarization, and the second by reflexions from the surfaces of metals at
angles varying from 70° 45' to 78° 30'. The motion of the wave in the first
is supposed to be circular, or to be that which is represented by looking
along the centre of a corkscrew as it is turned round. At every turn of the
medium effecting circular polarization the colour of the ray of light is
changed after a uniform order. If turned in one direction, they change
through red, orange, yellow, green, and violet; and if in the other direction,
the colours appear in the contrary order.
The variety of striking effects produced by the polarization of light; the
unexpected results which have sprung from the investigation of the laws by
which it is regulated; and the singular beauty of many of its phenomena,
have made it one of the most attractive subjects of modern science.
Ordinary light passes through transparent bodies without producing any
very striking effects in its passage; but this extraordinary beam of light has
the power of insinuating itself between the molecules of bodies, and by
illuminating them, and giving them every variety of prismatic hue, of

enabling the eye to detect something of the structure of the mass. The
chromatic phenomena of polarized light are so striking, that no description
can convey an adequate idea of their character.
Spectra more beautiful and intense than the prismatic image,—systems of
rings far excelling those of thin plates,—and forms of the most symmetric
order, are constantly presenting themselves, as the polarized ray is passed
through various transparent substances; the path of the ray indicating
whether the crystal has been formed round a single nucleus or axis, or
whether it has been produced by aggregation around two axes. The coloured
rings, and the dark or luminous crosses which distinguish the path of the
polarized ray, are respectively due to different states of tension amongst the
particles, although those differences are so slight, that no other means is of
sufficient delicacy to detect the variation.
The poetry which surrounds these, in every way, mysterious conditions of
the solar beam, is such, that it is with difficulty that imagination is
restrained by the stern features of truth. The uses of this peculiar property in
great natural phenomena are not yet made known to us; but, since we find
on every side of us the natural conditions for thus separating the beam of
light, and effecting its polarization, there must certainly be some most
important end for which it is designed by Him who said, “Let there be
Light.”
It must not be forgotten that we have at command the means of showing
that the chromatic phenomena of polarized light are due to atomic
arrangement. By altering the molecular arrangement of transparent bodies,
either by heat or by mere mechanical pressure, the unequal tension or strain
of the particles is at once indicated by means of the polarized ray of light
and its rings of colour. Differences in the chemical constitution of bodies,
too slight to be discovered by any other mode of analysis, can be most
readily and certainly detected by this luminous investigator of the molecular
forces.[101]
Although we cannot enter into an examination of all the conditions involved
in the polarization of, and the action of matter on, ordinary light, it will be
readily conceived, from what has been already stated, that some most
important properties are indicated, beyond those which science has made
known.

Almost every substance in nature, in some definite position, appears to have
the power of producing this change upon the solar ray, as may be
satisfactorily shown by examining them with a polarizing apparatus.[102]
The sky at all times furnishes polarized light, which is most intense where it
is blue and unclouded, and the point of maximum polarization is varied
according to the relative position of the sun and the observer. A knowledge
of this fact has led to the construction of a “Solar Clock,”[103] with which
the hour can be readily determined by examining the polarized condition of
the sky. It has been stated, that chemical change on the Daguerreotype
plates and on photographic papers is more readily produced by the
polarized than by the ordinary sunbeam.[104] If this fact be established by
future investigations, we advance a step towards the discovery so much
desiderated of the part it plays in natural operations.
The refined and accurate investigations of Dr. Faraday stand prominently
forward amid those which will redeem the present age from the charge of
being superficial, and they will, through all time, be referred to as illustrious
examples of the influence of a love of truth for truth’s sake, in entire
independence of the marketable value, which it has been unfortunately too
much the fashion to regard. The searching examination made by this
“interpreter of nature” into the phenomena of electricity in all its forms, has
led him onward to trace what connexion, if any, existed between this great
natural agent and the luminous principle.
By employing that subtile analyzer, a polarized ray, Dr. Faraday has been
enabled to detect and exhibit effects of a most startling character. He has
proved magnetism to have the power of influencing a ray of light in its
passage through transparent bodies. A polarized ray is passed through a
piece of glass or a crystal, or along the length of a tube filled with some
transparent fluid, and the line of its path carefully observed; if, when this is
done, the solid or fluid body is brought under powerful magnetic influence,
such as we have at command by making a very energetic voltaic current
circulate around a bar of soft iron, it will be found that the polarized light is
disturbed; that, indeed, it does not permeate the medium along the same
line.[105] This effect is most strikingly shown in bodies of the greatest
density, and diminished in fluids, the particles of which are easily moveable
over each other, and has not hitherto been observed in any gaseous medium.
The question, therefore, arises,—does magnetism act directly upon the ray

of light, or only indirectly, by producing a molecular change in the body
through which the ray is passing? This question, so important in its bearings
upon the connexion between the great physical powers, will, no doubt,
before long receive a satisfactory reply. A medium is necessary to the
production of the result, and, as the density of the medium increases, the
effect is enlarged: it would therefore appear to be due to a disturbance by
magnetic force of the particles which constitute the medium employed.
Without any desire to generalize too hastily, we cannot but express a
feeling,—amounting to a certainty in our own mind,—that those
manifestations of luminous power, connected with the phenomena of
terrestrial magnetism, which are so evident in all the circumstances
attendant upon the exhibition of Aurora Borealis, and those luminous clouds
which are often seen, independent of the Northern Lights, that a very
intimate, relation exists between the solar radiations and that power which
so strangely gives polarity to this globe of ours.
In connexion with the mysterious subject of solar light, it is important that
we should occupy a brief space in these pages with the phenomena of
vision, which is so directly dependent upon luminous radiation.
The human eye has been rightly called the “masterpiece of divine
mechanism;” its structure is complicated, yet all the adjustments of its parts
are as simple as they are perfect. The eye-ball consists of four coats. The
cornea is the transparent coat in front of the globe; it is the first optical
surface, and this is attached to the sclerotic membrane, filling up the
circular aperture in the white of the eye; the choroid coat is a very delicate
membrane, lining the sclerotic, and covered with a perfectly black pigment
on the inside; and close to this lies the most delicately reticulated
membrane, the retina, which is, indeed, an extension of the optic nerve.
These coats enclose three humours,—the aqueous, the vitreous, and the
crystalline humours.
The eye, in its more superficial mechanical arrangements, presents exactly
the same character as a camera obscura, the cornea and crystalline lens
receiving the images of objects refracting and inverting them; but how
infinitely more beautiful are all the arrangements of the organ of vision than
the dark chamber of Baptista Porta![106] The humours of the eye are for the
purpose of correcting the aberrations of light, which are so evident in

ordinary lenses, and for giving to the whole an achromatic character. Both
spherical and chromatic aberration are corrected, the latter not entirely, and
by the agency of the cornea and the crystalline lens perfect images are
depicted on the retina, in a similar way to those very charming pictures
which present themselves in the table of the camera obscura.
The seat of vision has been generally supposed to be the retina; but Mariotte
has shown that the base of the optic nerve, which is immediately connected
with the retina, is incapable of conveying an impression to the brain. The
choroid coat, which lies immediately behind the retina, is regarded by
Mariotte and Bernoulli as the more probable seat of vision. The retina,
being transparent, offers no obstruction to the passage of the light onward to
the black surface of the choroid coat, from which the vibrations are, in all
probability, communicated to the retina and conveyed to the brain. Howbeit,
upon one or the other of these delicate coats a distinct image is impressed
by light, and the communication made with the brain possibly by a
vibratory action. We may trace up the phenomena of vision to this point; we
may conceive undulations of light, differing in velocity and length of wave,
occasioning corresponding tremors in the neuralgic system of the eye; but
how these vibrations are to communicate correct impressions of length,
breadth, and thickness, no one has yet undertaken to explain.
It has, however, been justly said by Herschel:—
“It is the boast of science to have been able to trace so far the refined
contrivances of this most admirable organ, not its shame to find something
still concealed from scrutiny; for, however anatomists may differ on points
of structure, or physiologists dispute on modes of action, there is that in
what we do understand of the formation of the eye, so similar, and yet so
infinitely superior to a product of human ingenuity; such thought, such care,
such refinement, such advantage taken of the properties of natural agents
used as mere instruments for accomplishing a given end, as force upon us a
conviction of deliberate choice and premeditated design, more strongly,
perhaps, than any single contrivance to be found whether in art or nature,
and renders its study an object of the greatest interest.”[107]
Has the reader ever asked himself why it is, having two eyes, and
consequently two pictures produced upon the tablets of vision, that we see
only one object? According to the law of visible direction, all the rays

passing through the crystalline lenses converge to one point upon the retina,
—and as the two images are coincident and nearly identical, they can only
produce the sensation of one upon the brain.
When we look at any round object, as the ornamented moderator lamp
before us, first with one eye, and then with the other, we discover that, with
the right eye, we see most of the right-hand side of the lamp, and with the
left eye more of the left-hand side. These two images are combined, and we
see an object which we know to be round.
This is illustrated in a most interesting manner by the little optical
instrument, the Stereoscope. It consists either of two mirrors placed each at
an angle of 45°, or of two semi-lenses turned with their curved sides
towards each other. To view its phenomena, two pictures are obtained by
the camera obscura on photographic paper of any object in two positions,
corresponding with the conditions of viewing it with the two eyes. By the
mirrors or the lenses these dissimilar pictures are combined within the eye,
and the vision of an actually solid object is produced from the pictures
represented on a plane surface. Hence the name of the instrument; which
signifies, Solid I see.
Analogy is often of great value in indicating the direction in which to seek
for a truth; but analogical evidence, unless where the resemblance is very
striking, should be received with caution. Mankind are so ready to leap to
conclusions without the labour necessary for a faithful elucidation of the
truth, that too often a few points of resemblance are seized upon, and an
inference is drawn which is calculated to mislead.
There is an idea that the phenomena of sound bear a relation to those of
light,—that there exists a resemblance between the chromatic and the
diatonic scales. Sound, we know, is conveyed by the beating of material
particles—the air—upon the auditory membrane of the ear, which have
been set in motion by some distant disturbance of the medium through
which it passes. Light has been supposed to act on the optic nerve in the
same manner. If we imagine colour to be the result of vibrations of different
velocities and lengths, we can understand that under some of these tremors,
first established on the nerves, and through them conveyed to the brain,
sensations of pain or pleasure may result, in the same way as sharp or
subdued sounds are disagreeable or otherwise. Intensely coloured bodies do

make an impression upon perfectly blind men; and those who, being born
blind, know no condition of light or colour, will point out a difference
between strongly illuminated red and yellow media. When the eyes are
closed we are sensible to luminous influence, and even to differences of
colour. We must consequently infer that light produces some peculiar action
upon the system of nerves in general; this may or may not be independent
of the chemical agency of the solar radiations; but certainly the excitement
is not owing to any calorific influence. The system of nerves in the eye is
more delicately organized, and of course peculiarly adapted to all the
necessities of vision.
Thus far some analogy does appear to exist between light and sound; but
the phenomena of the one are so much more refined than those of the other
—the impressions being all of them of a far more complicated character,
that we must not be led too far by the analogical evidence in referring light,
like sound, to mere material motion.
It was a beautiful idea that real impressions of external objects are made
upon the seat of vision, and that they are viewed, as in a picture, by
something behind the screen,—that these pictures become dormant, but are
capable of being revived by the operations of the mind in peculiar
conditions; but we can only regard it as a philosophical speculation of a
poetic character, the truth or falsehood of which we are never likely to be
enabled to establish.[108]
That which sees will never itself be visible. The secret principle of
sensation,—the mystery of the life that is in us,—will never be unfolded to
finite minds.
Numerous experiments have been made from time to time on the influence
of light upon animal life. It has been proved that the excitement of the solar
rays is too great for the healthful growth of young animals; but, at the same
time, it appears probable that the development of the functional organs of
animals requires, in some way, the influence of the solar rays. This might,
indeed, have been inferred from the discovery that animal life ceases in
situations from which light is absolutely excluded. The instance of the
Proteus of the Illyrian lakes may appear against this conclusion. This
remarkable creature is found in the deep and dark recesses of the calcareous
rocks of Adelsburg, at Sittich; and it is stated, also in Sicily, and in the

Mammoth caves of Kentucky. Sir Humphry Davy describes the Proteus
anguinus as “an animal to whom the presence of light is not essential, and
who can live indifferently in air and in water, on the surface of the rock, or
in the depths of the mud.” The geological character of rocks, however,
renders it extremely probable that these animals may have descended with
the water, percolating through fissures from very near the surface of the
ground. All the facts with which science has made us acquainted—and both
natural and physical science has been labouring with most untiring industry
in the pursuit of truth—go to prove that light is absolutely necessary to
organization. It is possible the influence of the solar radiations may extend
beyond the powers of the human senses to detect luminous or thermic
action, and that consequently a development of animal and vegetable forms
may occur where the human eye can detect no light; and under such
conditions the Proteus may be produced in its cavernous abodes, and also
those creatures which live buried deep in mud. Some further consideration
of the probable agency of light will occupy us, when we come to examine
the phenomena of vital forces.
Light is essentially necessary to vegetable life; and to it science refers the
powers which the plant possesses of separating carbon from the air breathed
by the leaves, and secreting it within its tissues for the purpose of adding to
its woody structure. As, however, we have, in the growing plant, the action
of several physical powers exerted to different ends at the same time, the
remarkable facts which connect themselves with vegetable chemistry and
physiology are deferred for a separate examination.
The power of the solar rays to produce in bodies that peculiar gleaming
light which we call phosphorescence, and the curious conditions under
which this phenomenon is sometimes apparent, independent of the sun’s
direct influence, present a very remarkable chapter in the science of
luminous powers.
The phosphorescence of animals is amongst the most surprising of nature’s
phenomena, and it is not the less so from our almost entire ignorance of the
cause of it. Many very poetical fancies have been applied in description of
these luminous creations; and imagination has found reason why they
should be gifted with these extraordinary powers. The glow-worm lights her
lamp to lure her lover to her bower, and the luminous animalcules of the
ocean are employed in lighting up the fathomless depths where the sun’s

rays cannot penetrate, to aid its monsters in their search for prey. “The lamp
of love—the pharos—the telegraph of the night,—which scintillates and
marks, in the silence of darkness, the spot appointed for the lover’s
rendezvous,”[109] is but a pretty fiction; for the glow-worm shines in its
infant state, in that of the larva, and when in its aurelian condition. Of the
dark depths of the ocean it may be safely affirmed that no organized
creation lives or moves in its grave-like silence to require this fairy aid.
Fiction has frequently borrowed her creations from science. In these cases
science appears to have made free with the rights of fiction.
The glow-worms (lampyris noctiluca), it is well known, have the power of
emitting from their bodies a beautiful pale bluish-white light, shining during
the hours of night in the hedge-row, like crystal spheres. It appears, from
the observations of naturalists, that these insects never exhibit their light
without some motion of the body or legs;—from this it would seem that the
phosphorescence was dependent upon nervous action, regulated at pleasure
by the insect; for they certainly have the power of obscuring it entirely. If
the glow-worm is crushed, and the hands or face are rubbed with it,
luminous streaks, similar to those produced by phosphorus, appear. They
shine with greatly increased brilliancy in oxygen gas and in nitrous oxide.
From these facts may we not infer that the process by which this luminosity
is produced, whatever it may be, has a strong resemblance to that of
respiration?
There are several varieties of flies, and three species of beetles of the genus
Elater, which have the power of emitting luminous rays. The great lantern-
fly of South America is one of the most brilliant, a single insect giving
sufficient light to enable a person to read. In Surinam a very numerous class
of these insects are found, which often illuminate the air in a remarkable
manner. In some of the bogs of Ireland a worm exists which gives out a
bright green light; and there are many other kinds of creatures which, under
certain circumstances, become luminous in the dark. This is always
dependent upon vitality; for all these animals, when deprived of life, cease
to shine.
At the same time we have many very curious instances of phosphorescence
in dead animal and vegetable matter; the lobster among the Crustacea, and
the whiting among fishes, are striking examples; decayed wood also emits
much light under certain conditions of the atmosphere. This development of

light does not appear to be at all dependent upon putrefaction; indeed, as
this process progresses, the luminosity diminishes. We cannot but imagine
that this light is owing, in the first place, to direct absorption by, and
fixation within, the corpuscular structure of those bodies, and that it is
developed by the decomposition of the particles under the influence of our
oxygenous atmosphere.
The pale light emitted by phosphorus in the dark is well known; and this is
evidently only a species of slow combustion, a combination of the
phosphorus with the oxygen of the air. Where there is no oxygen,
phosphorus will not shine; its combustion in chlorine or iodine vapour is a
phenomenon of a totally different character from that which we are now
considering. This phosphorescence of animal and vegetable matter has been
regarded as something different from the slow combustion of phosphorus;
but, upon examination, all the chemical conditions are found to be the same,
and it is certainly due to a similar chemical change.
The luminous matter of the dead whiting or the mackerel may be separated
by a solution of common salt or of sulphate of magnesia; by concentrating
these solutions the light disappears; but it is again emitted when the fluid is
diluted. The entire subject is, however, involved in the mystery of
ignorance, although it is a matter quite within the scope of any industrious
observer. The self-emitted light of the carbuncle of the romancer is realized
in these remarkable phenomena.
The phosphorescence of some plants and flowers is not, perhaps, of the
same order as that which belongs to either of the conditions we have been
considering. It appears to be due rather to an absorption of light and its
subsequent liberation. If a nasturtium is plucked during sunshine, and
carried into a dark room, the eye, after it has reposed for a short time, will
discover the flower by a light emitted from its leaves.
The following remarkable example, and an explanation of it by the poet
Goethe, is instructive:—
“On the 19th of June, 1799, late in the evening, when the twilight was
deepening into a clear night, as I was walking up and down the garden with
a friend, we very distinctly observed a flame-like appearance near the
oriental poppy, the flowers of which are remarkable for their powerful red
colour. We approached the place, and looked attentively at the flowers, but

could perceive nothing further, till at last, by passing and repassing
repeatedly, while we looked side-ways on them, we succeeded in renewing
the appearance as often as we pleased. It proved to be a physiological
phenomenon, and the apparent corruscation was nothing but the spectrum
of the flower in the complementary blue-green colour. The twilight
accounts for the eye being in a perfect state of repose, and thus very
susceptible, and the colour of the poppy is sufficiently powerful in the
summer twilight of the longest days to act with full effect, and produce a
complementary image.”[110]
The leaves of the œnothera macrocarpa are said to exhibit phosphoric light
when the air is highly charged with electricity. The agarics of the olive-
grounds of Montpelier have been observed to be luminous at night; but they
are said to exhibit no light, even in darkness, during the day. The
subterranean passages of the coal mines near Dresden are illuminated by the
phosphorescent light of the rhizomorpha phosphoreus, a peculiar fungus.
On the leaves of the Pindoba palm, a species of agaric grows which is
exceedingly luminous at night; and many varieties of the lichens, creeping
along the roofs of caverns, lend to them an air of enchantment by the soft
and clear light which they diffuse. In a small cave near Penryn, a luminous
moss is abundant; and it is also found in the mines of Hesse. According to
Heinzmann, the rhizomorpha subterranea and aidulæ are also
phosphorescent.
It is but lately that a plant which abounds in the jungles in the Madura
district of the East Indies was sent to this country, which, although dead,
was remarkably phosphorescent; and, when in the living state, the light
which it emitted was extraordinarily vivid, illuminating the ground for some
distance. Those remarkable effects may be due, in some cases, to the
separation of phosphuretted hydrogen from decomposing matter, and, in
others, to some peculiar electric manifestation.
The phosphorescence of the sea, or that condition called by fishermen
brimy, when the surface, being struck by an oar, or the paddle-wheels of a
steamer, gives out large quantities of light, has been attributed to the
presence of myriads of minute insects which have the power of emitting
light when irritated. The night-shining nereis (Nereis noctiluca) emits a
light of great brilliancy, as do several kinds of the mollusca. The nereides
attach themselves to the scales of fishes, and thus frequently render them

exceedingly luminous. Some of the crustaceæ possess the same remarkable
property;—twelve different species of cancer were taken up by the
naturalists of the Zaire in the Gulf of Guinea.[111] The cancer fulgens,
discovered by Sir Joseph Banks, is enabled to illuminate its whole body,
and emits vivid flashes of light. Many of the medusæ also exhibit powerful
phosphorescence.[112] These noctilucous creatures are, many of them,
exceedingly minute, several thousands being found in a tea-cup of sea
water. They float near the surface in countless myriads, and when disturbed
they give out brilliant scintillations, often leaving a train of light behind
them.[113] By microscopic examination no other fact has been elicited than
that these minute beings contain a fluid which, when squeezed out, leaves a
line of light upon the surface of water. The appearance of these creatures is
almost invariably on the eve of some change of weather, which would lead
us to suppose that their luminous phenomena must be connected with
electrical excitation; and of this, the investigations of Mr. C. Peach, of
Fowey, communicated to the British Association at Birmingham, furnish the
most satisfactory proofs we have as yet obtained.
Benvenuto Cellini gave a curious account of a carbuncle which shone with
great brilliancy in the dark.[114] The same thing has been stated of the
diamond; but it appears to be necessary to procure these emissions of light,
that the minerals should be first warmed near a fire. From this it may be
inferred that the luminous appearance is of a similar character to that of
fluor spar, and of numerous other earthy minerals, which, when exposed to
heat, phosphoresce with great brilliancy. Phosphorescent glow can also be
excited in similar bodies by electricity, as was first pointed out by Father
Beccaria, and confirmed by Mr. Pearsall.[115] These effects, it must be
remembered, are distinct from the electric spark manifested upon breaking
white sugar in the dark, or scratching sulphuret of zinc.
In the instances adduced there is not necessarily any exposure to the
sunshine required. It is probable that two, if not three, distinct phenomena
are concerned in the cases above quoted, and that all of them are distinct
from animal phosphorescence, or the luminous appearance of vegetables.
They, however, certainly prove, either that light is capable of becoming
latent, or that it is only a condition of matter, in which it may be made
manifest by any disturbance of the molecular forces. We have, in answer to
this, very distinct evidence that some bodies do derive this property from

the solar rays. Canton’s phosphorus, which is a sulphuret of calcium, will,
having been exposed to the sun, continue luminous for some time after it is
carried into the dark; as will also the Bolognian stone,—a sulphuret of
barium. This result appears to be due to a particular class of the solar rays;
for it has been found, if these sulphurets, spread smoothly on paper, are
exposed to the influence of the solar spectrum for some little time, and then
examined in the dark, that luminous spaces appear, exactly corresponding
with the most refrangible rays, or those which excite chemical change; and
one very remarkable fact must not be forgotten—the dark rays of the
spectrum beyond the violet produce a lively phosphorescence, which is
extinguished by the action of the rays of least refrangibility, or the heat rays
—whilst artificial heat, such as a warm iron, produces a very considerable
elevation of the phosphorescent effect.[116] It is not improbable, that the
fluorescent rays of Mr. Stokes may be materially concerned in producing
the phenomena of phosphorescence: experiments are, however, required to
prove this.
In these allied phenomena we have effects which are evidently dependent
upon several dissimilar causes. The phosphorescence of the living animal is
due, without doubt, to nervous excitation: that of the living vegetable to
solar luminous influence; and in the case of the mosses of caverns, &c. to
the chemical agency of the sun’s rays, which appears to be capable of
conduction. In the dead organic matter we have a purely chemical action
developing the light, and in the inorganic bodies we have peculiar
molecular constitution, by which an absorption of light appears to take
place.
The subject is one of the greatest difficulty; the torch of science is too dim
to enable us to see the causes at work in producing these marvellous effects.
The investigation leads, to a certain extent, to the elucidation of many of the
secrets of luminous action; and the determination of the question, whether
light is an emanation from the sun, or only a subtile principle diffused
through all matter, which is excited by solar influence, is intimately
connected with the inquiry.
It has been stated that matter is necessary to the development of light; that
no luminous effect would be produced if it were not for the presence of
matter. Of this we not only have no proof, but such evidence as we have is
against the position. There is no loss of light in the most perfect vacuum we

can produce by any artificial means, which should be the case if matter was
concerned in the phenomena of light, as a cause.
Colour is certainly a property regulated by material bodies; or rather, the
presence of matter is necessary to the production of colour. Chlorine gas is
a pale yellow, and nitrous vapour a yellowish red. These and one or two
other vapours, which are near the point of condensation into fluids, are the
only coloured gaseous or vaporiform bodies. The sky is blue, because the
material particles of the atmosphere reflect back the blue rays. But we have
more practical illustrations than this. The flame of hydrogen burning with
oxygen gives scarcely any light; allow it to impinge on lime, a portion of
which is carried off by the heat of the flame, and the most intense artificial
light with which we are acquainted is produced. Hydrogen gas alone gives a
flame in which nearly all but the blue rays are wanting: place a brush of
steel or asbestos in it, and many of the other rays are at once produced. An
argand lamp, and more particularly the lamp in which camphine—a purified
turpentine,—is burnt, gives a flame which emits most of the rays found in
sunlight. Spirit of wine mixed with water, warmed and ignited, gives only
yellow rays; add nitrate of strontian and they become red; but nitrate of
barytes being mixed with the fluid, they are changed to green and yellow;
salts of copper afford fine blue rays, and common salt intense yellow ones.
Many of these coloured rays and others can be produced in great power by
the use of various solid bodies introduced into flame. This has not been
sufficiently pointed out by authors; but it is clear from experiments that
light requires the presence of matter to enable it to diffuse its coloured
glories. How is it that the oxygen and hydrogen flame gives so little light,
and with a solid body present, pours forth such a flood of brilliancy?
The production of artificial light by electrical and chemical agencies will
necessarily find some consideration under their respective heads. There are
numerous phenomena which connect themselves with luminous power, or
appear to do so, which, in the present state of our knowledge, cannot come
immediately under our attention. We are compelled to reserve our limited
space for those branches of science which we are enabled to connect with
the great natural operations constantly going on around us. Many of these
more abstruse results will, however, receive some incidental notice when
we come to examine the operation of the combined physical forces on
matter.

We see in light a principle which, if it has not its source in the sun, is
certainly dependent upon that luminary for its manifestations and powers.
From that “fountain of light” we find this principle travelling to us at a
speed which almost approaches the quickness of thought itself; yet by the
refinements of science we have been enabled to measure its velocity with
the utmost accuracy. The immortal poet of our own land and language, in
his creations of Ariel, that “tricksy spirit,” who could creep like music upon
the waters, and of the fantastic Puck, who could girdle the earth in thirty
minutes, appears to have approached to the highest point to which mere
imagination could carry the human mind as to the powers of things ethereal.
Science has, since then, shown to man that this “spirit, fine spirit,” was a
laggard in his tasks, and a gross piece of matter, when compared with the
subtile essences which man, like a nobler Prospero, has now subdued to do
him service.
Light is necessary to life; the world was a dead chaos before its creation,
and mute disorder would again be the consequence of its annihilation.
Every charm which spreads itself over this rolling globe is directly
dependent upon luminous power. Colours, and probably, forms, are the
result of light; certainly the consequence of solar radiations. We know much
of the mysterious influences of this great agent, but we know nothing of the
principle itself. The solar beam has been tortured through prismatic glasses
and natural crystals; every chemical agent has been tried upon it, every
electrical force in the most excited state brought to bear upon its operations,
with a view to the discovery of the most refined of earthly agencies; but it
has passed through every trial without revealing its secrets, and even the
effects which it produces in its path are unexplained problems, still to tax
the intellect of man.
Every animal and every plant alike proclaim that life and health are due to
light; and even the crystallizing forms of inorganic matter, by bending
towards it, confess its all-prevailing sway. From the sun to each planet
revolving around that orb, and to the remotest stars which gleam through
the vast immensity of heaven, we discover this power still in its brightness,
giving beauty and order to these unnumbered creations; no less completely
than to this small island of the universe which we call our Earth. Through
every form of matter we can mark its power, and from all, we can, under
certain conditions, evoke it in lustre and activity. Over all and through all

light spreads its ethereal force, and manifests, in all its operations, powers
which might well exalt the mind of Plato to the idea of an omniscient and
omnipresent God. Science, with her Ithuriel wand, has, however, shown
that light is itself the effect of a yet more exalted cause, which we cannot
reach.
Indeed, the attentive study of the fine abstractions of science lifts the mind
from the grossness of matter, step by step, to the refinements of
immateriality, and there appear, shadowed out beyond the physical forces
which man can test and try, other powers still ascending, until they reach
the Source of every good and every perfect gift.

FOOTNOTES:
[84] “These—oxygen, hydrogen, nitrogen, and carbon—are the four bodies, in
fact, which, becoming animated at the fire of the sun, the true torch of
Prometheus, approve themselves upon the earth the eternal agents of
organisation, of sensation, of motion and of thought.”—Dumas, Leçons de
Philosophie Chimique, p. 100. Paris, 1837.
[85] It will be found in examining any of the works of the alchemists,—
particularly those of Geber, De inveniendi arte Auri et Argenti, and his De
Alchemiâ; Roger Bacon’s Opus Majus, or Alchymia Major; Helvetius’ Brief of
the Golden Calf; or Basil Valentine’s Currus Triumphalis,—that in the processes
of transmutation the solar light was supposed to be marvellously effective. In
Boyle’s Sceptical Chemist the same idea will be found pervading it.
Amid all their errors, the alchemists were assiduous workmen, and to them we
are indebted for numerous facts. Of them, and of their age, as contrasted with
our own, Gibbon remarks:—“Congenial to the avarice of the human heart, it was
studied in China, as in Europe, with equal eagerness and equal success. The
darkness of the middle ages ensured a favourable reception to every tale of
wonder; and the revival of learning gave new vigour to hope, and suggested
more specious arts of deception. Philosophy, with the aid of experience, has at
length banished the study of alchemy; and the present age, however desirous of
riches, is content to seek them by the humbler means of commerce and
industry.”—Decline and Fall, vol. ii. p. 137.
[86] On the two theories the following maybe consulted:—Young, Supplement
to Encyclopædia Britannica, article Chromatics; Fresnel, Supplément à la
Traduction Française de la 5ième édition du Traité de Chimie de Thomson, par
Riffault, Paris, 1822; Herschel’s Article, Light, in the Encyclopædia
Metropolitana, and the French Translation of it by Quetelet and Verhulst; Airy’s
Tract on the Undulatory Theory, in his Tracts, 2nd edition, Cambridge, 1831;

Powel, The Undulatory Theory applied to Dispersion, &c. p. 184; Lloyd’s
Lectures, Dublin, 1836–41; Cauchy, Sur le Mouvement des Corps élastiques,
Mémoires de l’Institut, 1827, vol. ix. p. 114; Théorie de la Lumière, Ibid. vol. x.
p. 293; M’Cullagh, On Double Refraction, Ibid., vol. xvi.; Geometrical
Propositions applied to the Wave Theory of Light, Ibid., vol. xvii.; Sir David
Brewster’s papers in the Transactions of the Royal Society of Edinburgh, and the
Philosophical Magazine.
[87] Results of Astronomical Observations made during the years 1834–38, at
the Cape of Good Hope, &c. By Sir John Herschel, Bart., K.H., D.C.L., F.R.S.
—“In the contemplation of the infinite, in number and in magnitude, the mind
ever fails us. We stand appalled before this mighty spectre of boundless space,
and faltering reason sinks under the load of its bursting conceptions. But, placed
as we are on the great locomotive of our system, destined surely to complete at
least one round of its ethereal course, and learning that we can make no apparent
advance on our sidereal journey, we pant with new ardour for that distant bourne
which we constantly approach without the possibility of reaching it. In feeling
this disappointment, and patiently bearing it, let us endeavour to realise the great
truth from which it flows. It cannot occupy our mind without exalting and
improving it.”—Sir D. Brewster: North British Review.
[88] For examples of this, consult Graham’s Elements of Chemistry; Brande’s
Manual of Chemistry; or, indeed, any work treating of the science. The
formation of ink, by mixing two colourless solutions, one of gallic acid and
another of sulphate of iron, may be taken as a familiar instance.
[89] Sir John Herschel, in his paper On the Chemical Action of the Rays of the
Solar Spectrum on Preparations of Silver, remarks that, “it may seem too
hazardous to look for the cause of this very singular phenomenon in a real
difference between the chemical agencies of those rays which issue from the
central portion of the sun’s disc, and those which, emanating from its borders,
have undergone the absorptive action of a much greater depth of its atmosphere;
and yet I confess myself somewhat at a loss what other cause to assign for it. It
must suffice, however, to have thrown out the hint; remarking only, that I have
other, and, I am disposed to think, decisive evidence (which will find its place
elsewhere) of the existence of an absorptive solar atmosphere, extending beyond
the luminous one. The breadth of the border, I should observe, is small, not
exceeding 0·5 or 1/7 part of the sun’s radius, and this, from the circumstances of
the experiment, must necessarily err in excess.”—Philosophical Transactions,
1840.
[90] Experiments and Observations on some Cases of Lines in the Prismatic
Spectrum, produced by the passage of Light through Coloured Vapours and
Gases, and from certain Coloured Flames. By W. A. Miller, M.D., F.R.S.,
Professor of Chemistry in King’s College, London.—Philosophical Magazine,
vol. xxvii.
[91] Report on the Mollusca and Radiata of the Ægean Sea, and on their
distribution, considered as bearing on Geology. By Edward Forbes, F.R.S., &c.
—Reports of the British Association, vol. xii. Professor Forbes remarks:—“A
comparison of the testacea, and other animals of the lowest zones, with those of
the higher, exhibits a very great distinction in the hues of the species, those of
the depths being, for the most part, white or colourless, while those of the higher

regions, in a great number of instances, exhibit brilliant combinations of colour.
The results of an enquiry into this subject are as follows:—
“The majority of shells of the lowest zone are white or transparent; if tinted rose
is the hue, a very few exhibit markings of another colour. In the seventh region,
white species are also very abundant, though by no means forming a proportion
so great as the eighth. Brownish red, the prevalent hue of the brachiopoda, also
gives a character of colour to the fauna of this zone; the crustacea found in it are
red. In the sixth zone the colours become brighter, reds and yellows prevailing,
—generally, however, uniformly colouring the shell. In the fifth region many
species are banded or clouded with various combinations of colours, and the
number of white species has greatly diminished. In the fourth, purple hues are
frequent, and contrasts of colour common. In the second and third, green and
blue tints are met with, sometimes very vivid; but the gayest combinations of
colour are seen in the littoral zone, as well as the most brilliant whites.
“The animals of Testacea, and the Radiata of the higher zones, are much more
brilliantly coloured than those of the lower, where they are usually white,
whatever the hue of the shell may be. Thus the genus Trochus is an example of a
group of forms mostly presenting the most brilliant hues both of shell and
animal; but whilst the animals of such species as inhabit the littoral zone are
gaily chequered with many vivid hues, those of the greater depth, though their
shells are almost as brightly covered as the coverings of their allies nearer the
surface, have their animals, for the most part, of a uniform yellow or reddish
hue, or else entirely white. The chief cause of this increase of intensity of colour
as we ascend is, doubtless, the increased amount of light above a certain
depth.”—p. 172.
[92] Ἁμὁρφωτα. On the Epipolic Dispersion of Light, being a paper entitled, On
a case of Superficial Colour presented, by a homogeneous liquid internally
colourless. By Sir J. F. W. Herschel, Bart, K.H., F.R.S., &c.—An epipolized
beam of light (meaning thereby a beam which has once been transmitted through
a quiniferous solution, and undergone its dispersing action) is incapable of
further undergoing epipolic dispersion. In proof of this the following experiment
may be adduced,—
A glass jar being filled with a quiniferous solution, a piece of plate glass was
immersed in it vertically, so as to be entirely covered, and to present one face
directly to the incident light. In this situation, when viewed by an eye almost
perpendicularly over it, so as to graze either surface very obliquely, neither the
anterior nor posterior face showed the slightest trace of epipolic colour. Now, the
light, at its egress from the immersed glass, entered the liquid under precisely the
same circumstances as that which, when traversing the anterior surface of the
glass jar, underwent epipolic dispersion on first entering the liquid. It had,
therefore, lost a property which it originally possessed, and could not, therefore,
be considered qualitatively the same light.—Philosophical Transactions, vol.
cxxxvi.
[93] In connection with this view, the Newtonian theory should be consulted, for
which see—A Letter of Mr. Isaac Newton, Professor of the Mathematicks in the
University of Cambridge; containing his new Theory about Light and Colors:
sent by the Author to the Publisher, from Cambridge, Feb. 6, 1671–72, in order
to be communicated to the Royal Society.

[94] In that admirable work, The Physical Atlas of Dr. Berghaus, of which a very
complete edition by Alexander Keith Johnstone is published in this country, the
following order of the distribution of plants is given:—
1. The region of palms and bananas Equatorial zone.
2. Tree ferns and figs Tropical zone.
3. Myrtles and laurels Sub-tropical zone.
4. Evergreen trees Warm temperate zone.
5. European trees Cold temperate zone.
6. Pines Sub-arctic zone.
7. Rhododendrons Arctic zone.
8. Alpine plants Polar zone.
Consult Humboldt, Essai sur la Géographie des Plantes, Paris, 1807; De
Distributione Geographicâ Plantarum, Paris, 1817. Schouw, Grundzüge der
Pflanzengeographie. Also his Earth, Plants, and Man; translated by Henfrey, in
Bohn’s Scientific Library. Lamouroux, Géographie Physique. The Plant, a
Biography: by Schleiden; translated by Henfrey. Physical Geography: by Mrs.
Somerville.
[95] Fraunhofer’s measure of illuminating power is as follows:—
At the 22nd degree of the red 0·032
" 34th degree of the red 0·094
" 22nd degree of the orange 0·640
" 10th degree of the yellow 1·000
" 42nd degree of the yellow 0·480
" 2nd degree of the blue 0·170
" 16th degree of the indigo 0·031
" 43rd degree of the violet 0·0056
[96] Herschel, On the Action of Crystallized Bodies on Homogeneous Light, and
on the causes of the deviation from Newtons scale in the tints which many of
them develope on exposure to a polarized ray.—Phil. Trans., vol. cx., p. 88.
[97] On the Nature of Light and Colours: Lecture 39, in Young’s Lectures on
Natural Philosophy, Kelland’s Edition, p. 373, and the authorities there quoted.
[98] Brewster’s Optics: Lardner’s Cabinet Cyclopædia. Herschel, On Light:
Encyclopædia Metropolitana.
[99] Malus, Sur une Propriété de la Lumière Réfléchie: Mémoires d’Arcueil.
Numerous memoirs by Sir David Brewster, in the Philosophical Transactions.
[100] Bartholin, On Iceland Crystals: Copenhagen, 1669. An Accompt of sundry
Experiments made and communicated by that Learn’d Mathematician Dr.
Erasmus Bartholin, upon a Chrystal like Body sent to him out of Island: in
connection with which Dr. Matthias Paissenius writes:—The observations of the
excellent Bartholin upon the Island Chrystal are, indeed, considerable, as well as
painful. We have here, also, made some tryals of it upon a piece he presented me
with, which confirm his observations. Mean time he found it somewhat scissile

and reducible by a knife into thin laminas or plates, which, when single, shew’d
the object single, but laid upon one another shew’d it double; the two images
appearing the more distant from one another, the greater the number was of
those thin plates laid on one another. With submission to better judgements I
think it to be a kind of Selenites. Some of our curious men here were of opinion
that the Rhomboid figure proper to this stone was the cause of the appearances
doubled thereby. But having tryed whether in other transparent bodies of the like
figure the like would happen, we found no such thing in them, which made us
suspect some peculiarity in the very Body of the stone.—Phil. Trans. for 1670,
vol. v.
[101] On the Application of the Laws of Circular Polarization to the Researches
of Chemistry: by M. Biot.—Nouvelles Annales du Muséum d’Histoire Naturelle,
vol. iii., and Scientific Memoirs, vol. i. p. 600. On Circular Polarization: by Dr.
Leeson.—Memoirs of the Chemical Society.
[102] In Sir David Brewster’s Treatise On Optics, chap, xviii., On Polarization,
the best arrangements for a polarizing apparatus will be found described.
[103] This beautiful application was recently made by Professor Wheatstone, the
particulars of which will be found in his interesting communication.—On a
means of determining the apparent Solar Time by the diurnal changes of the
Plane of Polarization at the Northern Pole of the Sky: Report of the Eighteenth
Meeting of the British Association.
[104] On the Polarization of the Chemical Rays of Light: by John Sutherland,
M.D., in which the author refers to the following experiment of M. J. E. Bérard
—“I received the chemical rays directed into the plane of the meridian on an
unsilvered glass, under an incidence of 35° 61'. The rays reflected by the first
glass were received upon a second, under the same incidence. I found that when
this was turned towards the south, the muriate of silver exposed to the invisible
rays which it reflected was darkened in less than half an hour; whereas, when it
was turned towards the west, the muriate of silver exposed in the place where the
rays ought to have been reflected, was not darkened, although it was left exposed
for two hours. It is consequently to be presumed that the chemical rays can
undergo double refraction in traversing certain diaphanous bodies; and lastly, we
may say that they enjoy the same physical properties as light in general.”—
Philosophical Magazine, vol. xx.
Dr. Leeson has stated that Daguerreotype pictures can be taken more readily
under the influence of polarized light, than by ordinary radiation.
[105] On the Magnetization of Light, and the Illumination of Magnetic Lines of
Force: by Michael Faraday, D.C.L., F.R.S.—Philosophical Transactions, vol.
cxxxvii.—The following remarks are to the point of doubt referred to in the text.
—“The magnetic forces do not act on the ray of light directly and without the
intervention of matter, but through the mediation of the substance in which they
and the ray have a simultaneous existence; the substances and the forces giving
to and receiving from each other the power of acting on the light. This is shown
by the non-action of a vacuum, of air or gases, and it is also further shown by the
special degree in which different matters possess the property. That magnetic
force acts upon the ray of light always with the same character of manner, and in
the same direction, independent of the different varieties of substance, or their
states of solid or liquid, or their specific rotative force, shows that the magnetic

force and the light have a direct relation; but that substances are necessary, and
that these act in different degrees, shows that the magnetism and the light act on
each other through the intervention of the matter. Recognising or perceiving
matter only by its powers, and knowing nothing of any imaginary nucleus
abstract from the idea of these powers, the phenomena described must
strengthen my inclination to trust in the views I have advanced in reference to its
nature.”—Phil. Mag. vol. xxiv.
[106] The invention of the camera obscura certainly belongs to Giambattista
Porta, and is described in his Magiæ Naturalis, sive de Miraculis Rerum
Naturalium, Libri Viginti; Antwerp, 1561. An English translation made in 1658
exists, but I have not seen it.
Hooke, in one of the earliest volumes of the Philosophical Transactions,
describes as new many of the phenomena mentioned by Porta, and particularly
the images of the dark chamber.
[107] Herschel, On Light,—Encyclopædia Metropolitana.
[108] “I would here observe that a consideration of many such phenomena (the
obliteration and revival of photographic drawings) has led me to regard it as not
impossible that the retina itself may be photographically impressed by strong
light, and that some at least of the phenomena of visual spectra and secondary
colours may arise from the sensorial perception of actual changes in progress in
the physical state of that organ itself subsequent to the cessation of the direct
stimulant.”—On the action of the Rays of the Solar Spectrum on Vegetable
Colours, &c.: by Sir J. F. W. Herschel, Bart.
[109] Dumeril.
[110] Theory of Colours: by Goethe; translated by Eastlake.
[111] See Tuckey’s Narrative of the Expedition of the Zaire.
[112] The most complete examination of this subject will be found in two
Memoirs:—
1. Experiments and observations on the light which is spontaneously emitted
with some degree, of permanency from various bodies.—Phil. Trans., vol. xc.
2. A continuation of the above, with some experiments and observations on solar
light, when imbibed by Canton’s phosphorus: by Nathaniel Hulm, M.D.—Phil.
Trans., vol. xci.; and in the Monograph of the British Naked-eyed Medusæ, by
Professor Edward Forbes (published for the Ray Society). See Wilson’s note to
the account of Pennalata phosphorea in Johnston’s Zoophytes, 2nd edition.
[113] A General Outline of the Animal Kingdom: by Thomas Rymer Jones,
F.L.S.—Acalephæ, p. 64. Lettre à M. Dumas sur la Phosphorescence des Vers
luisants: par M. Ch. Matteucci.—Annales de Chimie, vol. ix. p. 71, 1843.
[114] Memoirs of Benvenuto Cellini—Bohn’s Standard Library. See also his
Treatise on his Art as a Sculptor and Engraver. Florence, 1568. 4to.
[115] Phosphorescence of the Diamond: by M. Reiss (Revue Scientifique et
Industrielle, vol. xxiii. p. 185).—“The diamond, phosphorescent by insulation,
lost rapidly its phosphorescence when submitted to the action of the red rays of
the solar spectrum. On the contrary, the blue rays are those which render the

diamond the most luminous in the dark. It is probable that the phosphorescence
produced by heat is equally diminished by the action of the red rays of the solar
spectrum.” Giovanni Battista Beccaria published his experiments in 1769. See
Priestley’s History of Electricity; and On the Effects of Electricity upon Minerals
which are Phosphorescent by Heat; and Further Experiments on the
communication of Phosphorescence and Colour to bodies of Electricity; by
Thomas J. Pearsall.—Journal of the Royal Institution of Great Britain, Oct.
1830, Feb. 1831.—These two memoirs contain the most complete set of
experiments on this subject which have yet been made; see Placidus Heinrich,
Phosphorescenz der Körper, vol. iv.; Gmelin’s Handbuch der Chemie, part 1.;—
On the Phosphorescence of Minerals, Brewster: Edinburgh Philosophical
Journal, vol. i. p. 137.;—The Aërial Noctiluca, or some New Phenomena, and a
process of a factitious self shining substance: Boyle’s Works, vol. iv.
[116] Des Effets produits sur les corps par les Rayons Solaires: par M. Edmond
Becquerel.—Annales de Chimie, vol. ix. p. 257. 1843.
M. Becquerel has applied the term phosphorogénique to those rays producing
phosphorescence.

CHAPTER VIII.
ACTINISM—CHEMICAL RADIATIONS.
The Sun-ray and its Powers—Darkening of Horn Silver—
Niepce’s Discovery—Prismatic Spectrum—Refrangibility of
Light, Heat, and Actinism—Daguerre’s Discovery—
Photography—Chemical Effects produced by Solar
Radiations—Absorption of Actinism—Phenomena of the
Daguerreotype—Chemical Change produced upon all
Bodies—Power of Matter to restore its Condition—Light
protects from Chemical Change—Photographs taken in
Darkness—Chemical Effects of Light on organized Forms—
Chemical Effects of Solar Heat—Influence of Actinism on
Electricity—Radiations in Darkness—Moser’s Discoveries,
&c.

Heat and light are derived from the sun, and we have attempted to show, not
only that the phenomena of these two principles are different, but that they
can scarcely, in the present condition of our knowledge, be regarded as
modified manifestations of one superior power. Associated with these two
remarkable elements, others may exist in the solar rays. Electrical
phenomena are certainly developed by both heat and light, and peculiar
electric changes are produced by exposure to sunshine. Electricity may be
merely excited by the solar rays, or it may flow like light from the sun.
Chemical action may be only due to the disturbance of some diffused
principle; or it may be directly owing to some agency which is radiated at
once from the sun.
A sun ray is a magical thing: we connect it in our fancy with the most
ethereal of possible creations. Yet in its action on matter it produces colour;
it separates the particles of solid masses farther from each other, and it
breaks up some of the strongest forces of chemical affinity. To modern
science is entirely due the knowledge we have gained of the marvellous
powers of the sunbeam; and it has rendered us familiar with phenomena, to

which the incantation scenes of the Cornelius Agrippas of the dark ages
were but ill-contrived delusions, and their magic mirrors poor instruments.
The silver tablets of the photographic artist receiving fixed impressions of
the objects represented in the dark chamber by a lens, are far superior as
examples of natural magic.
In the dark ages, or rather as the earliest gleams of the bright morning of
inductive research were dispelling the mists of that phantom-peopled
period, it was observed, for the first time, that the sun’s rays turned a white
compound black. Man must have witnessed, long before, that change which
is constantly taking place in all vegetable colours: some darkening by
exposure to sunlight, while others were bleached by its influence. Yet those
phenomena excited no attention, and the world knew nothing of the mighty
changes which were constantly taking place around them. The alchemists—
sublime pictures of credulous humanity—toiling in the smoke of their
secret laboratories, waiting and watching for every change which could be
produced by fire, or by their “royal waters,” caught the first faint ray of an
opening truth; and their wild fancy, that light could change silver into gold,
if they but succeeded in getting its subtile beams to interpenetrate the metal,
was the clue afforded to the empirical philosopher to guide him through a
more than Cretan labyrinth.[117]
The first fact recorded upon this, point was, that horn silver blackened when
exposed to the light. Without doubt many anxious thoughts were given by
these alchemists to that fact. Here was, as it appeared, a mixing up of light
and matter, and behold the striking change! It was a step towards the
realization of their dreams. Alas! poor visionaries! in pursuing an ideality
they lost the reality which was within their grasp.
Truths come slowly upon man, and long it is before these angel visits are
acknowledged by humanity. The world clings to its errors, and avoids the
truth, lest its light should betray their miserable follies.
At length a man of genius announced that “No substance can be exposed to
the sun’s rays without undergoing a chemical change;” but his words fell
idly upon the ear. His friends looked upon his light-produced pictures as
singular; they preserved them in their cabinets of curiosities; but the truths
which he enunciated were soon forgotten. Howbeit his words were
recorded, and it is due to the solitary experimentalist of Châlons on the

Saône, to couple the name of Niepce with the discovery of a fact which is
scarcely second to the development of the great law of universal
gravitation.[118] But an examination awaits us, which, for its novelty, has
more charms than most branches of science, and which, for the extensive
views it opens to the inquirer, has an interest in nowise inferior to any other
physical investigation.
The prismatic spectrum affords us the means of examining the conditions of
the solar rays with great facility. In bending the ray of white light out of its
path, by means of a triangular piece of glass, we divide it in a remarkable
manner. We learn that heat is less refracted by the glass than the other
powers; we find the maximum point of the calorific rays but slightly thrown
out of the right line, which the solar pencil would have taken, had it not
been interrupted by the prism; and the thermic action is found to diminish
with much regularity on either side of this line. We discover that the
luminous power is subject to greater refraction, and that its maximum lies
considerably above that of heat; and that, in like manner, on each side the
light diminishes, producing orange, red, and crimson colours below the
maximum point, and green, blue, and violet above it. Again, we find that
the radiations which produce chemical change are more refrangible than
either of the others, and the maximum of this power is found at the point
where light rapidly diminishes, and where scarcely any heat can be
detected: it extends in full activity, above its maximum, to a considerable
distance, where no trace of light under ordinary conditions exists, and
below that point, until light, appearing to act as an interfering agent,
quenches its peculiar properties. These are strong evidences that light and
actinism—as this principle has been named—are not identical: and we may
separate them most easily and effectually from each other. Certain glasses,
stained dark blue, with oxide of cobalt, admit scarcely any light; but they
offer no interruption to the passage of actinism or the chemical rays; on the
contrary, a pure yellow glass, or a yellow fluid, which does not sensibly
reduce the intensity of any one colour of the chromatic band of luminous
rays, completely cuts off this chemical principle, whatever it may be. In
addition to these, there are other results which we shall have to describe,
which prove that, although associated in the solar beam, light and actinism
are in constant antagonism.

When Daguerre first published his great discovery, the European public
regarded his metal tablets with feelings of wonder: we have grown
accustomed to the beautiful phenomena of this art, and we have become
acquainted with a number of no less beautiful processes on paper, all of
which, if studied aright, must convince the most superficial thinker, that a
world of wonder lies a little beyond our knowledge, but within the reach of
industrious and patient research. Photography is the name by which the art
of sun-painting will be for ever known. We regard this as unfortunate,
conveying as it does a false idea,—the pictures not being light-drawn.
Could we adopt the name given by Niepce to the process, the difficulty
would be avoided, since Heliography involves no hypothesis, and strictly
tells the undeniable truth, that our pictures are sun-drawn. That pictures can
be produced by the rays from artificial sources, presents no objection to
this; these rays were still originally derived from the sun.
By whatever name we determine to convey our ideas of these phenomena, it
is certain that they involve a series of effects which are of the highest
interest to every lover of nature, and of the utmost importance to the artist
and the amateur. By easy manipulation we are now enabled to give
permanence to the charming pictures which are produced by means of that
pleasing invention of Baptista Porta, the Camera Obscura. Any image,
which being refracted by the lens of this instrument falls upon the table in
its dark chamber, may be secured with its most delicate gradations of
shadows, upon either a metallic or a paper tablet.
But let us proceed to the examination of a few of the more striking
phenomena of these chemical changes. To commence with some of the
more simple but no less important results.
Chlorine and hydrogen will not unite in darkness, nor will chlorine and
carbonic oxide; but, if either of those gaseous mixtures is exposed to
sunshine, they combine rapidly, and often with explosion. A solution of the
sulphate of iron in ordinary water may be preserved for a long time in the
dark without undergoing any change; expose it to the sunshine, and a
precipitation of oxide of iron is very rapidly produced. The mineral
chameleon, the manganesiate of potash in solution, is almost instantly
decomposed in daylight; but it is a long time before it undergoes any
change in darkness. The same thing occurs with a combination of platinum
and lime: indeed, it appears that precipitation is at all times, and under all

circumstances, accelerated by the solar rays. As these precipitations are in
exact agreement with the quantity of actinic radiation to which the solutions
have been exposed, we may actually weigh off the relative quantities,
representing in grains the equivalent numbers to the amount of actinism
which has influenced the chemical compound.[119]
We have evidence which appears to prove that this chemical agent may be
absorbed by simple bodies, and that by this absorption an actual change of
condition, is produced, in many respects analogous to those allotropic
changes which we have previously considered. Chlorine, in its ordinary
state, does not combine with hydrogen in the dark. If we employ the yellow
medium of chlorine gas, for the purpose of analyzing the sun’s rays
previously to their falling upon some chemical compound which is sensitive
to actinic power, we shall find that the chlorine obstructs all this actinism,
and, however unstable the compound, it remains unchanged. But the
chlorine gas which has interrupted this wonderful agent, appears to have
absorbed it, and it is so far altered in its constitution that it will unite with
hydrogen in the dark.[120] In like manner, if, of two portions of the same
solution of sulphate of iron, one is kept in the dark and the other exposed to
the sunshine, it will be found that the solution which has been exposed will
precipitate gold and silver from their combinations much more speedily
than that which has been preserved in darkness—the temperature and every
other condition being the same.
The phenomena of the Daguerreotype involve many strange conditions. A
plate of silver, on which a slight chemical action has been established by the
use of iodine, is exposed to the lenticular image in the camera obscura. If
allowed to remain under the influence of these radiations for a sufficient
length of time, a faithful picture of the illuminated objects is delineated on
the plate, as shown by the visible decomposition and darkening of the
iodized surface. The plate is not, however, in practice allowed to assume
this condition; after an exposure of a few seconds the radiant influence is
cut off, and the eye cannot detect any evidence of change upon the yellow
plate. It is now exposed to the vapour of mercury, and that metal in a state
of exceedingly fine division is condensed upon the plate; but the
condensation is not uniformly spread upon its face. The deposit of mercurial
vapour is in exact proportion to the amount of chemical action produced. Is
the change, by which this peculiar power of condensation is effected, a

chemical, calorific, electrical, or merely a molecular one? The evidences, at
present, are not sufficient to determine the question. It has lately been
suggested, that the mercury acts chemically only, and effects the full
decomposition of the iodide of silver; and that the picture is due to this, and
not to the deposition actually of the mercury vapour. In all probability we
have the involved action of several forces. We have some experiments
which show, clearly enough, that mercury is deposited in proportions which
correspond with the intensity of solar action. A chemically prepared surface
is not necessary to exhibit this result. A polished plate of metal, of glass, of
marble, or a piece of painted wood, being partially exposed, will, when
breathed upon, or presented to the action of mercurial vapour, show that a
disturbance has been produced upon the portions which were illuminated,
whereas no change can be detected upon the parts which were kept in the
dark. It was thought, until lately, that a few chemical compounds, such as
the iodide of silver, the material employed in the Daguerreotype and
Calotype,—chloride of silver, the ordinary photographic agent,—a few salts
of gold, and one or two of lead and iron, were the only materials upon
which these very remarkable changes were produced. We now know that it
is impossible to expose any body, simple or compound, to the sun’s rays,
without its being influenced by this chemical and molecular disturbing
power. To take our examples from inorganic nature, the granite rock which
presents its uplifted head in firmness to the driving storm, the stones which
genius has framed into forms of architectural beauty, or the metal which is
intended to commemorate the great acts of man, and which in the human
form proclaims the hero’s deeds and the artist’s talent, are all alike
destructively acted upon during the hours of sunshine, and, but for
provisions of nature no less wonderful, would soon perish under the
delicate touch of the most subtile of the agencies of the universe.
Niepce was the first to show that all bodies which underwent this change
during daylight possessed the power of restoring themselves to their
original conditions during the hours of night, when this excitement was no
longer influencing them. Resins, the Daguerreotype plate, the unprepared
metal tablet, and numerous photographic preparations, prove this in a
remarkable manner.[121]
The picture which we receive to-day, unless we adopt some method of
securing its permanency, fades away before the morrow, and we try to

restore it in vain. With some of our chemical preparations this is very
remarkably shown, but by none in so striking a manner as by paper
prepared with the iodide of platinum, which, being impressed with an image
by heliographic power, which is represented by dark brown tints, restores
itself in the dark, in a few minutes, to its former state of a yellow colour,
and recovers its sensibility to sunshine.[122] The inference we alone can
draw from all the evidences which the study of actino-chemistry affords, is,
that the hours of darkness are as necessary to the inorganic creation as we
know night and sleep to be to the organic kingdom. But we must not forget
that there does exist in the solar rays a balance of forces which materially
modifies the amount of disturbing influence exerted by them on matter. Not
only do we find that the chemical action is not extended over the whole
length of the prismatic spectrum, but we discover that over spaces, which
correspond with the maximum points of light and heat, a protective action is
exerted. That is, that highly sensitive photographic agents, which blacken
rapidly under exposure to diffused daylight, are entirely protected from
change in full sunshine, if at the same time as a strong light is thrown upon
them by reflection, the yellow and extra red rays are brought to bear upon
their surface. Not only so, but by employing media which will cut off all the
chemical rays of the spectrum, admitting freely at the same time the
luminous and calorific rays, we find that a protected band, the length of the
spectrum, remains white, whilst every other portion has blackened.[123]
Among the many curious instances of natural magic, none are more
remarkable than an experiment not long since proposed, by which
Daguerreotype pictures may be taken in absolute darkness to the human
eye. This is effected in the following manner:—A large prismatic spectrum
is thrown upon a lens fitted into one side of a dark chamber; and as we
know that the actinic power resides in great activity beyond the violet ray,
where there is no light, the only rays which we allow to pass the lens into
the chamber are those which are extra-spectral and non-luminous. These are
directed upon, any white object, and from that object radiated upon a highly
sensitive plate in a camera obscura. Thus a copy of the subject will be
obtained by the agency of radiations which produce no sensible effect upon
the optic nerve. This experiment is the converse of those which show us that
we may illuminate any object with the strongest sunlight which has passed
through yellow glass, the yellow solution of sulphuret of calcium, or of the

bichromate of potash—these being non-transparent to the chemical rays—
and yet fail to secure any Daguerreotype copy of it, even upon the most
exquisitely sensitive plate. Indeed, the image of the sun itself, when setting
through an atmosphere which reduces its light to a red or rich yellow
colour, not only produces no chemical change, but protects an iodized plate
from it; and whilst every other part of the tablet gives a picture of
surrounding objects in the ordinary character, the bright sun itself is
represented by a spot upon which no change has taken place.[124] In tropical
climes, where a brilliant sun is giving the utmost degree of illumination to
all surrounding objects, all photographic preparations are acted upon
relatively more slowly than in the climate of England, where the light is less
intense. As a remarkable instance of this fact, a circumstance may be
mentioned, which is curiously illustrative of the power of light to interfere
with actinism:—
A gentleman, well acquainted with the Daguerreotype process, obtained in
the city of Mexico all the necessary apparatus and chemicals, expecting,
under the bright light and cloudless skies of that climate, to produce
pictures of superior excellence. Failure upon failure was the result; and
although every care was used, and every precaution adopted, it was not
until the rainy season set in that he could secure a good Daguerreotype of
any of the buildings of that southern city.
The first attempts, which were made at the instigation of M. Arago, by
order of the French Government, to copy the Egyptian tombs and temples,
and the remains of the Aztecs in Central America, were failures. Although
the photographers employed succeeded to admiration in Paris, in producing
pictures in a few minutes, they found often that an exposure of an hour was
insufficient under the bright and glowing illumination of a southern sky.
Experiments with the spectrum have been made in different latitudes, and it
is found, that, as we proceed towards the equator, a band which is always
left unchanged, corresponding exactly with the rays of greatest illuminating
power, regularly enlarges in size, thus proving the increase of light over
actinism—and the interfering power of the former.
By increasing the sensibility of the photographic preparation, this difficulty
is overcome, and particularly when any organic compound enters into the
preparation. So that we are now enabled to copy nature in all her varying

moods, whether we employ our photographic tablets in temperate Europe,
or in tropical Africa.
The degree of sensibility which has been attained is remarkable. Mr. Fox
Talbot, by uniting a process devised by Dr. Woods, of Parsonstown, and
another which was first introduced by the author of this volume, and
combining them with an ether, obtains a most unstable compound, which he
thus employs. A glass plate is covered with albumen united with the above
solution, and then with nitrate of silver: this forms the sensitive surface. The
plate being placed in the dark, in a camera, it is so adjusted that the image
of a printed bill fixed upon a wheel may fall upon it when uncovered, and
the wheel illuminated. The wheel is made to revolve with the utmost
rapidity, in a perfectly dark room, and the sensitive plate uncovered. Then
the whirling bill is illuminated for an inappreciably short space of time by
the discharge of a Leyden jar. Notwithstanding the rapid rate at which the
pointed paper is moving, and the instantaneous nature of the illumination—
a miniature flash of lightning—the bill is found to be copied with unfailing
fidelity upon the photographic plate. It unfortunately happens, that the
preparation by which this extraordinary degree of sensibility is obtained, is
very uncertain in its action—and hence it is not generally useful; but here
we have the evidence to show that at a speed as rapid as that of a rifle-ball
an impression may be made upon a photographic plate. There are, however,
some new processes which promise eventually to rival the above for
sensibility, and to be by no means of difficult manipulation. Of this
character is the collodion process. The gun cotton dissolved in ether
possesses some very great accelerating properties, and in combination with
the silver salts, and one of the vegetable acids, it forms a sensitive surface
upon which pictures may be obtained in less than a second of time.
Colour, natural colour too, has been very decidedly secured. The sun has
been solicited to display his palette, and the answer has been a picture in
which colour for colour in all their fidelity have been impressed. The plate
upon which this result has been obtained is of a dark brown colour, and the
chromatic variety is, as it were, eaten out by the solar rays. These colours
have not yet been permanently fixed upon the plate employed, but from the
temporary degree of fixedness which has been obtained, we may fairly hope
that in a short time colour may be rendered as permanent on the productions
of the photographer as on those of the painter. It is a curious and striking

fact, that in the preparation of these plates, salts are used which give colours
to flame; and according to the colour which is produced by them when
burning, so, on the photographic plate, is that colour impressed with greater
intensity than the others. To what is this leading us? Mysteries surround our
advances on the domain of truth. We dare not speculate upon them: the time
of their full development will arrive.
By the aid of this beautiful art, we are enabled to preserve the lineaments of
those who have benefited their race by their intellect, or their heroism. We
can hand down to future ages portraits of our own Wellington, and the
illustrious Arago, unerring in their truthfulness. How great would be the joy
of all, could we now obtain a daguerreotype portrait of a Greek poet, or of a
Roman philosopher, of a Sophocles, or of a Seneca! How much discussion
would be prevented did we possess a calotype portrait of the Bard of Avon,
or of the Philosopher of Grantham!
By the agency of those very rays which give life and brilliancy to the
laughing eye and the roseate cheek, we can at once correctly trace the
outline of the features we admire, with all those shadowy details which give
a reality to the “presentment.” The objects of our love may be for ever
present with us in these self-painted pictures. The vicious, whom we would
avoid, may be made known to us by this unerring painter. The process
which nature employs is perfect; the imperfections are those of man, and
these being few, he may soon learn to remedy.
To the traveller, how valuable are the processes of photography! He secures
representations of those remains of temples which were in their glory when
Moses wrote. He copies by one operation a tomb at Karnac, covered with
myriads of hieroglyphics, or an inscribed stone in Arabia, which it would
occupy him days to trace. These he can carry to his home and read at his
leisure. The relics of hoar antiquity speaking to the present of the past, and
recording the histories of races which have fleeted away like shadows, are
thus preserved to tell their wondrous tales.
The admirer of nature may copy her arrangements with the utmost fidelity.
Every modulation of the landscape, each projecting rock or beetling tor—
the sinuous river in its rapid flow—the meandering stream, “gliding like
happiness away;” and the spreading plains over which are scattered the
homes of honest industry and domestic peace, intermingled with the towers

of those humble temples in which simple-hearted piety delights to “bow the
head and bend their knee;” these, all of these, may, by the sunbeam which
illuminates the whole, be faithfully pencilled upon our chemical
preparations.
Our art enables us to do more even than this; we have but to present our
sensitive tablet to the moon, and she, by her own light, prints her mountains
and her valleys, and indicates with all truth the physical conditions of her
surface.
Any reference to the chemical agency of light—the luminous rays as
distinguished from the chemical and calorific rays—has been avoided until
we came to the consideration of this particular question of chemical change.
Upon organic compounds, as, for instance, upon the colouring matter of
leaves and flowers, light does exert a chemical power: and it is found that
vegetable colours are bleached, not by rays of their own colour, but by those
which are complementary to them. A red dye fades under the influence of a
green ray, and a yellow under that of a violet one, much more speedily than
when exposed to rays of any other colour; and this, it must be remembered,
is due to the coloured ray itself, and not to any actinic power masked, as it
were, behind the colour, as is generally believed.[125] It was long a question
whether the decomposition of carbonic acid by plants was due to the
luminous or the chemical rays. It is now clearly established that the
luminous rays are the most active in producing this effect; which they do
indirectly, by exciting the vital powers of the organized structures.
Therefore we would refer this phenomenon of gaseous decomposition to a
vital power quickened by luminous excitement.[126]
We have already noticed some chemical phenomena due to heat,
particularly those experiments of Count Rumford’s, which appeared to him
to prove that the chemical agency of the sun’s rays was due to its calorific
power. Certain chemical phenomena, we know, may be produced by
thermic action; but the only variety of thermo-chemical action which
connects itself immediately with the solar radiations, belongs to a class of
rays to which the name of Parathermic has been given, and to which the
scorching, as it is called, of plants, the browning of the autumnal leaves,
and the ripening of fruits, appear to be due.[127] When we come to the

consideration of those physical phenomena which belong to the growth of
plants, all these peculiarities of solar action must be attended to in detail.
The manner in which we find the actinic power influencing electrical
action, also shows us that the equilibrium of forces is continued through all
the great principles of nature. If a galvanic arrangement is made, by which
small quantities of metals may be slowly precipitated at one of the poles in
the dark, and a similar arrangement be exposed to sunshine, it will be found
that no metal is deposited: the sun’s rays have interfered with the
decomposing power of the electrical current. At the same time we learn,
that by throwing a beam of light upon a plate of copper which forms one of
a galvanic pair, whilst it is under the influence of an acidulated solution, an
additional excitation takes place, and the galvanometer will indicate the
passage of an increased current of electricity. These two dissimilar actions
appear enigmatical; but they may, there is no doubt, receive some solution
from the influence of different rays on the contrary poles of the battery. One
thing is quite evident,—electricity suffers a disturbance of one order, by
light; and an excitement of another by its associated principles in the
sunbeam. If a yellow glass is interposed between the galvanic arrangement
and the sun, the electro-chemical precipitation goes on in the same manner
as it would in perfect darkness, and no extra excitement is produced upon
the plates of the battery. From this it would appear that actinism and not
light is to be regarded as the disturbing power.[128] It has already been
shown that yellow media possess the power of stopping back the chemical
agent.
We have already, detailed many of the peculiarities of the different varieties
of Phosphori, which would seem to be the result of light. Phosphorescence
is probably excited by those rays which produce no direct effect upon the
eye. If we spread sulphuret of calcium upon paper, and expose it to the
action of the solar spectrum, it is found to glow (in the dark) only over
those spaces occupied by the violet rays and the ordinarily dark rays beyond
them; proving that the excitation necessary to the development of the
phenomena of phosphorescence is due to a class of rays distinct from the
true light-giving principle, and more nearly allied to that principle or power
which sets up chemical decomposition. Whether the fluorescent rays, before
mentioned, which are found so abundantly over the space which produces

the greatest phosphorescent effect, are active in producing the phenomena,
is as yet an unsolved problem.
Vision and colour, calorific action, chemical change, molecular disturbance,
electrical phenomena, and phosphorescent excitation, all, each one with a
strange duality, are connected with the sunbeam.
We find, when we receive solar spectra upon iodized plates, or on several
kinds of photographic paper, that a line, over which no action takes place, is
preserved at the top and bottom of the impressed image, and in many cases
along the sides also. The only way in which this can be accounted for, as the
spectrum represents the sun in a distorted form, is by supposing that rays
come from the edges of the sun of a different character from those which
proceed from the centre of that orb.[129]
Light from the centre of the solar disc is under different conditions from
that which comes from the edge of the sun: this is due to the varying angle,
which is presented to us by a circular body: calorific action seems to be
more strongly manifested when the envelope of light, extending like an
atmosphere to the sun, is thrown into great agitation, and waves, and great
hollows—solar spots—are produced. There is some indication of the
existence of a third condition on the sun’s surface, to which probably
belongs the mighty chemical power which we call actinism. Electricity may
be, as some have speculated, the exciting agent; a constant and violent
Aurora Borealis may exist on the sun, and under the excitation of this force
the others named may be quickened into full activity.
That actinism is one of the great powers of creation we have abundant
proof. Nearly all the phenomena of chemical change which have been
referred to light, are now proved to be dependent upon actinic power; and
beyond the influence which has been ascertained to be exerted by it upon all
inorganic bodies, we shall have occasion to show still further the
dependence of the vegetable and animal worlds upon its agency. The
influence of the solar beams on vegetation is proved by common
experience; the closer examination of its action on vegetable life is reserved
for the chapter devoted to its phenomena. Of its influence on animals
nothing is very correctly known; but some early experiments prove that
they, like other organised bodies, are subject to all the radiant forces, as
indeed, independent of experiment, every observation must teach. Certain it

is, that organisation can take place only where the sun’s rays can penetrate:
where there is unchanging darkness, there we find all the silence of death.
Prometheus stole fire from heaven, and gave the sacred gift to man, as the
most useful to him of all things in his necessities: by the aid of it he could
temper the severities of climate, render his food more digestible and
agreeable, and illuminate the hours of darkness. So says the beautiful fiction
of the Grecian mind,—which appears as the poetic dream or prophetic
glance of a gifted race, who felt the mysterious truth they were yet unable to
describe. Pheaton and Apollo are only other foreshadowings of the creative
energies which dwell in the glorious centre of our universe. The poetry of
the Hellenic people ascended above the littlenesses of merely human action,
and sought to interpret the great truths of creation. Reflective, they could
not but see that some mysterious powers were at work around them;
imaginative, they gave to fine idealisations the government of those
inexplicable phenomena. Modern science has shown what vastly important
offices the solar rays execute, and that the principles discovered in a
sunbeam are indeed the exciters of organic life, and the disposers of
inorganic form.
It must not be forgotten that we have already alluded to a speculation which
supposes this actinic influence to be diffused through all nature, to be
indeed the element to which chemical force in all its forms is to be referred,
and that it is merely excited by the solar rays. This hypothesis receives
some support from the very peculiar manner in which chemical action once
set up is carried on, independent of all extraneous excitement, after the first
disturbance has been produced. If any of the salts of gold are exposed in
connection with organic matter, as on paper, to sunshine for a moment, an
action is begun, which goes on unceasingly in the dark, until the gold is
reduced to its most simple state.[130] The same thing occurs with chromate
of silver, some of the salts of mercury, argentine preparations combined
with protosulphate of iron or gallic acid, and some other chemical
combinations. These progressive influences point to some law not yet
discovered, which seems to link this radiant actinism with the chemical
agent existing in all matter.
This problem also connects itself with another class of facts which,
although due, in all probability, to a great extent, to calorific radiations, and
hence known under the general term of Thermography, appear to involve

both chemical and electrical excitation. From the investigations of Moser
and of others, we learn the very extraordinary fact, that even inanimate
masses act and react upon each other by the influence of some dark
radiations, and seem to exchange some of the peculiarities which they
possess. This appears generally in the curious experiments which have been
referred to, as confined merely to form or structure. Thus an engraved plate
will give to a polished surface of metal or glass placed near it, after a very
little time, a neat distinct image of itself; that is, produce such a structural
disturbance as will occasion the plate to receive vapour differently over
those spaces opposite to the parts in cameo or in intaglio, from what it does
over the opposite. If a piece of wood is used instead of a metal, there will,
by similar treatment, be produced a true picture of the wood, even to the
representation of its fibres.[131]
It is also probable that chemical decomposition is produced by the mere
juxtaposition of different bodies. Iodide of gold or silver, perfectly pure, has
been placed upon a plate of glass, and a plate of copper covered with
mercury suspended over it: a gradual decomposition of those salts is said to
have been observed, iodide of mercury to be formed, and the gold or silver
salts reduced to a finely divided metallic state.[132]
A body whose powers of radiating heat are low, being brought near another
whose radiating powers are more extensive, will, in the course of a short
time, undergo such an amount of molecular disturbance as will effect a
complete change in the arrangement of its surface, and an impression of the
body having the highest radiating powers will be made upon the other. This
impression is dormant, but may be developed under the influence of vapour,
or of oxidation.[133] A body, such as charcoal, of low conducting power,
being placed near another, such as copper, which is a good conductor, will,
in a very short time, produce, in like manner, an impression of itself upon
the metal plate. Thus any two bodies, whose conducting or radiating powers
are dissimilar, being brought near each other, will occasion a molecular
disturbance, or impress the one with the image of the other. However small
the difference may be, an effect is perceived, and that of the most
extraordinary kind, giving rise to the production of actual images upon each
surface exposed. It is thus that a print on paper may be copied on metal, by
merely suspending it near a well-polished plate of silver or copper for a few
days. The white and black lines radiate very differently; consequently an

effect is produced on the bright metal in the parts corresponding to the
black lines, dissimilar to that which takes place opposite to the white
portions of the paper; and, on the application of vapour, a true image of the
one is found impressed upon the other.[134]
Bodies which are in different electrical states act upon each other in an
analogous manner. Thus arsenic, which is highly electro-negative, will,
when placed near a piece of electro-positive copper, readily impart to its
surface an impression of itself, and so in like manner will other bodies if in
unlike conditions. Every substance physically different (it signifies not
whether as it regards colour, chemical composition, mechanical structure,
calorific condition, or electrical state,) has a power of radiation by which a
sensible change can be produced in a body differently constituted.
Fable has told us that the magicians of the East possessed mirrors in which
they could at will produce images of the absent. Science now shows us that
representations quite sufficient to deceive the credulous can be produced on
the surface of polished metals without difficulty. A highly polished plate of
steel may be impressed with images of any kind, which would remain
invisible, the polished surface not being in the least degree affected, as it
regards its reflecting powers; but by breathing over it, the dormant images
would develope themselves, and fade away again as the condensed moisture
evaporated from the surface.[135]
These, which are but a few selected from a series of results of an equally
striking character, serve to convince us that nature is unceasingly at work,
that every atom is possessed of properties by which it influences every
other atom in the universe, and that a most important class of natural
phenomena appear to connect themselves directly with the radiant forces.
The alchemists observed that a change took place in chloride of silver
exposed to sunshine. Wedgwood first took advantage of that discovery to
copy pictures. Niepce pursued a physical investigation of the curious
change, and found that all bodies were influenced by this principle radiated
from the sun. Daguerre produced effects from the solar pencil which no
artist could approach to; and Talbot and others extended the application.
Herschel took up the inquiry; and he, with his usual power of inductive
search and of philosophical deduction, presented the world with a class of
discoveries which showed how vast a field of investigation was opening for

the younger races of mankind,—a field in which a true spirit may reap the
highest reward in the discovery of new facts, and to which we must look for
a further development of those great powers with which we have already
some slight acquaintance, and for the discovery of higher influences which
are not yet dreamed of in our philosophy.

If music, with its mysteries of sound,
Gives to the human heart a heavenward feeling;
The beauty and the grandeur which are found
Spread like a vesture this fair earth around,
Creation’s wond’rous harmonies revealing,
And to the soul in truth’s strong tongue appealing,
With all the magic of those secret powers,
Which, mingling with the lovely band of light,
The sun in constant undulation showers
To mould the crystals, and to shape the flowers,
Or give to matter the immortal might
Of an embracing soul—should, from this sod,
Exalt our aspirations all to God.

FOOTNOTES:
[117] See Researches on Light, by the Author.—Reference to any of the works
of the alchemists will prove the prevalence of the idea expressed in the text. We
find that gold was considered to be always under the influence of light and solar
heat.—“It is said of gold that it waxeth cold towards daylight, insomuch that
they who wear rings of it may perceive when the day is ready to dawn.”—
Speculum Mundi, or a Glass representing the face of the World. Cambridge,
1643.
[118] Daguerre’s Report to the Academy of Sciences: La Daguerréotype
Historique, et description des procédés du Daguerréotype et du Diorama (Paris,
1839); particularly the description of Heliography, by M. Niepce. See also the
letters by Niepce, published for the first time in Researches on Light.
[119] “If a solution of peroxalate of iron be kept in a dark place, or if it be
exposed to 212° of Fahr. for several hours, it does not undergo any sensible
change in its physical properties, nor does it exhibit any phenomenon which may
be considered as the result of any elementary action.

“If, however, it be exposed to the influence of solar light in a glass vessel
provided with a tube, the concentrated solution of oxalate of iron soon presents a
very interesting phenomenon: in a short time the solution receiving the solar
rays, developes an infinite number of bubbles of gas, which rise in the liquor
with increasing rapidity, and give the solution the appearance of a syrup
undergoing strong fermentation. This ebullition always becomes stronger, and
almost tumultuous, when an unpolished glass tube is immersed in it with a small
piece of wood; the liquid itself is afterwards thrown into ascending and
descending currents, becomes gradually yellowish, turbid, and eventually
precipitates protoxalate of iron, in the form of small brilliant crystals of a lemon-
yellow colour, gas continuing to evolve.” Chemical action of light, and
formation of Humboldtine by it; Phil. Mag., 1832, second series.—“When a
solution of platinum in nitro-muriatic acid, in which the excess of acid has been
neutralized by the addition of lime, and which has been well cleared by
filtration, is mixed with lime-water in the dark, no precipitation to any
considerable extent takes place for a long while,—indeed, none whatever,
though after very long standing a slight flocky sediment is formed, after which
the action is arrested entirely. But if the mixture, either freshly made or when
cleared by subsidence of this sediment, is exposed to sunshine, it instantly
becomes milky, and a copious formation of a white precipitate (or a pale yellow
one, if the platinic solution be in excess) takes place, which subsides quickly and
is easily collected. The same takes place more slowly in cloudy daylight.”—On
the action of light in determining the precipitation of Muriate of Platinum by
Lime water; being an extract from a letter from Sir John F. W. Herschel, K.H.,
F.R.S., &c., to Dr. Daubeny.—Phil. Mag. 1832.
[120] On a change produced by Exposure to the Beams of the Sun, in the
properties of an elementary substance, by Professor Draper; On the changes
which bodies undergo in the dark, by Robert Hunt: Report of the Thirteenth
Meeting of the British Association, vol. xii,—Description of the Tithonometer,
an instrument for measuring the chemical force of the Indigo-tithonic rays: by J.
W. Draper, M.D.—Philosophical Magazine, Dec. 1843, vol. xxiii.
[121] For several illustrations of this remarkable phenomenon, see On the Action
of the Rays of the Solar Spectrum on Vegetable Colours, and on some new
Photographic Processes; by Sir John F. W. Herschel, Bart., K.H., F.R.S.—Phil.
Trans. June, 1842, vol. cxxxiii.; On certain improvements on Photographic
Processes described in a former communication, and on the Parathermic Rays
of the Solar Spectrum; by Sir John F. W. Herschel, Bart., K.H., F.R.S., &c., in a
letter addressed to S. Hunter Christie.—Phil. Trans. 1843, vol. cxxxiv.
[122] Sir J. F. W. Herschel; see also Researches on Light, by the Author.
[123] Attention has been directed to the protecting action of certain rays of the
spectrum by Sir John Herschel and others. See the Eighteenth Report of the
British Association for an experiment by the Author, in which it was proved that
all the light rays protected photographic papers from chemical change, and,
therefore, convincingly show that light and actinism were not similar powers.
[124] “Having noticed, one densely foggy day, that the disc of the sun was of a
deep red colour, I directed my apparatus towards it. After ten seconds of
exposure, I put the prepared plate in the mercury box, and I obtained a round
image perfectly black;—the sun had produced no photogenic effect. In another

experiment, I left the plate operating for twenty minutes; the sun had passed over
a certain space of the plate, and there resulted an image seven or eight times the
sun’s diameter in length; it was black throughout, so that it was evident,
wherever the red disc of the sun had passed, not only was there a want of
photogenic action, but the red rays had destroyed the effect produced previous to
the sun’s passage. I repeated these experiments during several days successively,
operating with a sun of different tints of red and yellow. These different tints
produced nearly the same effect; wherever the sun had passed, there existed a
black band.”—Mr. Claudet, On different properties of Solar Radiation, modified
by coloured glass media, &c.: Phil. Trans. 1847. Part 2.
[125] “It may also be observed that the rays effective in destroying a given tint
are, in a great many cases, those whose union produces a colour complementary
to the tint destroyed, or at least one belonging to that class of colours to which
such complementary tint may be referred. For example, yellows tending towards
orange are destroyed with more energy by the blue rays; blue by the red, orange,
and yellow rays; purples and pinks by yellow and green rays.”—Sir J. F. W.
Herschel, On the action of the rays of the Solar Spectrum on Vegetable Colours:
Phil. Trans., vol. cxxxiii. 1842.
[126] The following memoirs and works are necessary to a complete history of
the inquiry:—Experiments and observations relating to various branches of
natural philosophy, with a continuation of the observation on air: by Dr.
Priestley. London, 1779. Mémoires Physico-chimiques, &c.: by J. Senebier.
Expériences sur les végétaux, by De la Ville: Paris, 1782; and Phil. Trans. 1782.
Observations sur les expériences de M. Ingenhousz: by De la Ville; Roz. obs. 23,
290. Expériences propres à développer les effets de la lumière sur certaines
plantes: by Tessier; Mém. de l’Ac. des Sc. de Paris, 1783, p. 132; Licht. Mag. iv.
4, 146. Sur la vertu de l’eau impregnée d’air fixe pour en obtenir, par le moyen
des plantes et de la lumière du soleil, de l’air déphlogistiqué: by Ingenhousz;
Roz. obs. 24, 337. Expériences sur l’action de la lumière solaire dans la
végétation: by Senebier; Genève et Paris, 1788, p. 61. Extrait des expériences de
M. Senebier sur l’action de la lumière solaire dans la végétation: by Hasenfratz;
Ann. Chim. iii. 2nd. ser. 266. Expériences relatives à l’influence de la lumière
sur quelques végétaux: by De Candolle; Jour. de Ph. lii. 124: Voigt’s Mag. ii.
483; Gilb. Ann. xiii. 372; Mém. des Sav. Etr. i. 329. Recherches chimiques sur la
végétation: by Saussure; Ann. Chim. l. 225; Jour. de Ph. lvii. p. 393; Gilb. Ann.
xviii 208. Recherches sur la respiration des plantes exposées à la lumière du
soleil; by Ruhland; Ann. Ch. Ph. iii. 411; Jour. de Ph. 1816. On the action of
light upon plants, and of plants upon the atmosphere: by Dr. Daubeny; Phil.
Trans. cxxvii January, 1836. On the action of yellow light in producing the green
colour, and of indigo light on the movements of plants: by P. Gardner; Phil. Mag.
xxiv.; Bibl. Univ. xlix. p. 376, and lii. p. 381. On the influence of light on plants:
by R. Hunt; Phil. Mag. xxiv. p. 96; Bibl. Univ. xlix. p. 383; Athen. 1844. Note on
the decomposition of carbonic acid by the leaves of plants, under the influence
of yellow light: by Draper; Phil. Mag. xxv. p. 169. On the action of the yellow
rays of light on vegetation: by Harkness; Phil. Mag. xxv. p. 339. Influence des
rayons solaires sur la végétation: by Zantedeschi; Inst. No. 541, p. 157.
[127] Sir John Herschel’s Memoirs already referred to; and Reports on the
influence of the Solar Rays on the growth of Plants, by Robert Hunt: Report of
the British Association for the Advancement of Science, for 1847.

[128] Memoir on the Constitution of the Solar Spectrum, presented at the
meeting of the Academy of Sciences, 1842, by M. Edmond Becquerel; Des effets
produits sur les corps par les rayons solaires, par M. Edmond Becquerel, aide
au Muséum d’Histoire Naturelle: Mémoire présenté à l’Académie des Sciences,
le 23 Octobre, 1843.—“Dans le courant de ce mémoire, j’ai employé les noms
de rayons lumineux, chimiques, et phosphorogéniques, pour désigner, dans
chaque cas, la portion des rayons solaires qui agit pour produire, en particulier,
les effets lumineux, chimiques, et phosphorogéniques; mais cela est sans
préjudice de l’opinion que je viens d’émettre touchant l’existence d’un seul et
même rayonnement.”
“My reply is this,” says M. Arago, in his paper entitled Considerations relative
to the action of Light: “It is by no means proved that the photogenic
modifications of sensitive substances result from the action of the solar light
itself. The modifications are, perhaps, engendered by invisible radiations mixed
with light properly so called, proceeding with it, and being similarly refracted. In
this case, the experiment would prove not only that the spectrum formed by
these invisible rays is not continuous, that there are solutions of continuity as in
the visible spectrum, but also that in the two superposed spectra these solutions
correspond exactly. This would be one of the most curious, one of the most
strange results of physics.”—Taylor’s Scientific Memoirs.
[129] The chemical evidence of this will be found in Sir John Herschel’s
Memoir On the Solar Spectrum, and particularly as exemplified in the changes
produced on the tartrate of silver. Similar influences are described as observed
on a Daguerreotype plate, in a paper entitled Experiments and Observations on
Light which has permeated coloured media, and on the Chemical Action of the
Solar Spectrum; by Robert Hunt.—Philosophical Magazine, vol. xxvi. 1840.
[130] This peculiar continuance of an effect has frequently been observed in
many of the photographic processes. In a note to a memoir On certain
improvements in Photographic processes, Sir John Herschel thus refers to this
property:—“The excitement is produced on such paper by the ordinary moisture
of the atmosphere, and goes on slowly working its effect in the dark, apparently
without other limit than is afforded by the supply of ingredients present. In the
case of silver it ultimately produces a perfect silvering of all the sunned portions.
Very singular and beautiful photographs, having much resemblance to
Daguerreotype pictures, are thus produced; the negative character changing by
keeping, and by quite insensible gradations to positive, and the shades exhibiting
a most singular chatoyant change of colour from ruddy-brown to black, when
held more or less obliquely. No doubt, also, gold pictures with the metallic lustre
might be obtained by the same process, though I have not tried the experiment.”
[131] The details of this curious subject may be studied in the following memoir
and communications:—On vision and the action of light on all bodies: by
Professor Ludwig Moser, of Königsberg; from Poggendorff’s Annalen, vol. lvi.
p. 177, No. 6, 1845. Some remarks on Invisible Light: by Professor Ludwig
Moser, of Königsberg; from Poggendorff’s Annalen, vol. lvi. p. 569, No. 8. On
the power which light possesses of becoming latent: by Professor Ludwig Moser,
of Königsberg; from Poggendorff’s Annalen, vol. lvii. No. 9, p. 1. 1842. On
certain spectral appearances, and on the discovery of latent light: by J. W.
Draper, M.D., Professor of Chemistry in the University of New York; Phil. Mag.
p. 348, Nov. 1842. On a new imponderable substance, and on a class of

chemical rays analogous to the rays of dark heat: by Professor Draper; Phil.
Mag., Dec. 1842. On the action of the rays of the solar spectrum on the
Daguerreotype plate; by Sir J. F. W. Herschel, Bart.; Phil. Mag., Feb. 1843. See
remarks in this paper on the use which Moser has made of coloured glasses: also
a communication by Professor Draper, On the rapid Detithonizing power of
certain gases and vapours, and on an instantaneous means of producing spectral
appearances: Phil. Mag., March 1843; and On the causes which concur in the
production of the images of Moser: Comptes Rendus, Nov. 1842. See Scientific
Memoirs, vol. iii.
[132] This fact was first observed by myself, and described in the paper already
referred to, Philosophical Magazine, vol. xxii. p. 270. It does not, however,
appear to have attracted the attention of any other observer.
[133] On Thermography, or the Art of copying Engravings or any printed
characters from paper or plates of metal, and on the recent discovery of Moser,
relative to the formation of images in the dark, by Robert Hunt: Reports of the
Royal Cornwall Polytechnic Society for 1842, and Philosophical Magazine, vol.
xxi. p. 462.—On the Spectral Images of M. Moser, by Robert Hunt:
Philosophical Magazine, vol. xxiii. p. 415.
[134] Catalytic force, or attraction of surface concerned in the diffusive power
of gases: an occult energy or power in saturated saline solutions; Prater.—
Mechanic’s Magazine, vol. xlv. p. 106. Ueber elektrische Abbildungen; by G.
Karsten.—Poggendorff’s Annalen, vol. lvii. p. 402.—Melloni and Brewster may
be consulted for much that is most remarkable connected with radiation from
coloured surfaces.
[135] Cornelius Agrippa is said to have possessed such a mirror. The Chinese
make mirrors which, when placed in a particular light, show upon their polished
faces the pattern on the back of the metal, although it is invisible in every other
position. This is effected by giving different degrees of hardness to the various
parts of the metal. In Natural Magic, by Sir David Brewster, several curious
experiments belonging to this class are named.

CHAPTER IX.
ELECTRICITY.
Discovery of Electrical Force—Diffused through all Matter—
What is Electricity?—Theories—Frictional Electricity—
Conducting Power of Bodies—Hypothesis of two Fluids—
Electrical Images—Galvanic Electricity—Effects on
Animals—Chemistry of Galvanic Battery—Electricity of a
Drop of Water—Electro-chemical Action—Electrical
Currents—Thermo-Electricity—Animal Electricity—
Gymnotus—Torpedo—Atmospheric Electricity—Lightning
Conductors—Earth’s Magnetism due to Electrical Currents
—Influence on Vitality—Animal and Vegetable
Development—Terrestrial Currents—Electricity of Mineral
Veins—Electrotype—Influence of Heat, Light, and Actinism
on Electrical Phenomena.

If a piece of amber, electrum, is briskly rubbed, it acquires the property of
attracting light bodies. This curious power excited the attention of Thales of
Miletus; and from the investigations of this Grecian philosopher we must
date our knowledge of one of the most important of the natural forces—
Electricity.
If an inquiring mind had not been led to ask why does this curious natural
production attract a feather, the present age, in all probability, would not
have been in possession of the means by which it is enabled to transmit
intelligence with a rapidity which equals the poet’s dream of the “swift-
winged messengers of thought.” To this age of application a striking lesson
does this amber teach. Modern utility would have regarded Thales as a
madman. Holding a piece of yellow resin in his hand, rubbing it, and then
picking up bits of down, or catching floating feathers, the old Greek would
have appeared a very imbecile, and the cui bono generation would have
laughed at his silly labours. But when he announced to his school that this
amber held a soul or essence, which was awakened by friction, and went

forth from the body in which it previously lay dormant, and brought back
the small particles floating around it, he gave to the world the first hint of a
great truth which has advanced our knowledge of physical phenomena in a
marvellous manner, and ministered to the refinements and to the necessities
of civilisation. Each phenomenon which presents itself to us, however
simple it may appear to be, is an outward expression of some internal truth,
the interpretation of which is only to be arrived at by assiduous study, but
which, once discovered, directs the way to new knowledge, and gives to
man a great increase of power. There is no truth so abstract that it will not
find its useful application, and every example of the ministration of
Physical Science to the purposes of humanity is an evidence of the value of
abstract study, and a reply to the utilitarian in his own language.
Electricity appears to be diffused through all nature; and it is, beyond all
doubt, one of the most important of the physical forces, in the great
phenomena of creation. In the thunder-cloud, swelling with destruction, it
resides, ready to launch its darts and shake the earth with its explosions: in
the aërial undulations, silent and unseen, it passes, giving the necessary
excitement to the organisms around which it floats. The rain-drop—the
earth-girdling ocean—and the ringing waters of the hill-born river, hold
locked this mighty force. The solid rocks—the tenacious clays which rest
upon them—the superficial soils—and the incoherent sands, give us
evidence of the presence of this agency; and in the organic world, whether
animal or vegetable, the excitement of electrical force is always to be
detected.
In the solar radiations we have perhaps the prime mover of this power. In
our atmosphere, when calm and cloudless, a great ocean of light, or when
sombre with the mighty aspect of the dire tornado, we can constantly detect
the struggle between the elements of matter to maintain an equilibrium of
electrical force.
Diffused throughout matter, electricity is ever active; but it must be
remembered that although it is evidently a necessary agent in all the
operations of nature, that it is not the agent to which everything unknown is
to be referred. Doubtless the influence of this force is more extensive than
we have yet discovered; but that is an indolent philosophy which refers,
without examination, every mysterious phenomenon to the influence of
electricity.

The question, what is electricity? has ever perplexed, and still continues to
agitate, the world of science. While one set of experimentalists have
endeavoured to explain the phenomena they have witnessed, upon the
theory that electricity is a peculiar subtile fluid pervading matter, and
possessing singular powers of attraction and repulsion, another party find
themselves compelled to regard the phenomena as giving evidence of the
action of two fluids which are always in opposite states; while again,
electricity has been considered by others as, like the attraction of
gravitation, a mere property of matter.[136] Certain it is, that in the
manifestations of electrical phenomena we have, as it appears, the evidence
of two conditions of force; but of the states of positive or negative, of
vitreous or resinous electricity, we have a familiar explanation in the
assumption of some current flowing into or out of the material body,—of
some principle which is ever active in maintaining its equilibrium, which,
consequently, must act in two directions, and always exhibit that duality
which is a striking characteristic of this subtile agent. It is a curious, and it
should be an instructive fact, that each of the three theories of electricity is
capable of proof, and has, indeed, been most ably supported by the rigorous
analysis of mathematics. When we remember that some of the most
enlightened investigators of this and the past age have severally maintained,
in the most able manner, these dissimilar views, we should hesitate before
we pronounce an opinion upon the cause or causes of the very complicated
phenomena of electrical force.
Although we discover, in all the processes of nature, the manifestations of
this principle or force in its characteristic conditions, it will be necessary,
before we regard the great phenomena, to examine the known sources from
which we can most readily evoke the mighty power of electricity. If we rub
a piece of glass or resin, we readily render this agent active; these
substances appear, by this excitement, to become surrounded by an
attractive or a repellent atmosphere. Let us rub a strip of writing paper with
Indian rubber, or a strip of Gutta Percha with the fingers, in the dark, and
we have the manifestation of several curious phenomena. We have a
peculiar attracting power; we have a luminous discharge in the shape of a
spark; and we have very sensible evidence of muscular disturbance
produced by applying the knuckle to the surface of the material. In each
case we have the development of the same power.

Every substance in nature is an electric, and, if so disposed that its
electricity may not fly off as it is developed, we may, by friction, manifest
its presence, and, indeed, measure its quantity or its force. All bodies are
not, however, equally good electrics; shell-lac, amber, resins, sulphur, and
glass, exhibiting more powerfully the phenomena of frictional or
mechanical electricity, than the metals, charcoal, or plumbago. Solid bodies
allow this peculiar principle to pass along them also in very different
degrees. Thus electricity travels readily through copper and most other
metals, platinum being the worst metallic conductor. It also passes through
living animals and vegetables, smoke, vapour, rarified air, and moist earth;
but it is obstructed by resins and glass, paper when dry, oils, and dry
metallic oxides, and in a very powerful manner by Gutta Percha.[137]
If, therefore, we place an electric upon any of those non-conducting bodies,
the air around being well dried, we are enabled to gather a large quantity of
the force for the production of any particular effect. Taking advantage of
this fact, arrangements are made for the accumulation and liberation at
pleasure of any amount of electricity.
A Leyden phial,—so called from its inventor, Musschenbroek, having
resided at Leyden,—is merely a glass bottle lined within and without, to
within a few inches of the top, with a metal coating. If a wire or chain,
carrying an electric current, is allowed to dip to the bottom of the bottle, the
inner coat of the jar becomes charged, or gathers an excess, whilst the outer
one is in its natural condition—one is said to be in a positive, and the other
in a negative state. If the two coatings are now connected by a good
conductor, as a piece of copper wire, passing from one to the other, the
outside to the inside, a discharge, arising from the establishment of the
equilibrium of the two coatings, takes place; and, if the connection is made
through the medium of our bodies, we are sensible of a severe disturbance
of the nervous system.
The cause of the conducting and non-conducting powers of bodies we know
not; they bear some relation to their conducting powers for caloric; but they
are not in exact obedience to the same laws. When we consider that resin, a
comparatively soft body, in which, consequently, cohesive attraction is not
very strong, is an imperfect conductor, and that copper, in which cohesion is
much more powerful, is a good conductor, we may be disposed to consider
that it is regulated by the closer approximation of the particles of matter.

But in platinum the corpuscular arrangement must be much more dense
than it is in copper, and yet it is, compared with it, a very bad conductor.
[138]

We have now learnt that we may, by friction, excite the electricity in a
vitreous substance; but it must not be forgotten that we cannot increase the
quantity which is, under ordinary conditions, natural to the electric; to do
so, we must in some way establish a channel of communication with the
earth, from which, through the medium we excite, we draw our supply. We
have the means of confining this mighty force within certain limits of
quantity and of time. If we place bodies which are susceptible of electrical
excitation in a sensible degree upon insulating ones, we may retain for a
considerable time the evidences of the excitement, in the same way as with
the Leyden jar; but there is a constant effort to maintain a balance of
conditions, and the body in which we have accumulated any extraordinary
quantity by conduction soon returns to its natural state.
A very simple means may be adopted of showing what is thought to be one
of the many evidences in favour of two electricities. If the wire carrying the
current flowing from the machine, is passed over paper covered with nitrate
of silver, it produces no change upon it; but if the wire which conveys the
current to the instrument, when it is excited, is passed over the same paper,
the silver salt is decomposed.[139] We may, however, explain this result in a
satisfactory manner, upon the hypothesis that the decomposition is
produced by the abstraction of electricity, rather than by any physical
difference in the fluid itself. By frictional electricity we may produce
curious molecular disturbances, and give rise to molecular re-arrangements,
which have been called “electrical images,” in glass, in stone, and in the
apparently less tractable metals: these images are rendered visible by the
manner in which, according to their electrical states, some lines receive any
particular powder, or vapour, which is repelled from other spaces. Many of
the great natural phenomena, such as Lightning and Thunder, the Aurora
Borealis, and Meteors, may be imitated in a curiously exact manner by the
electrical machine and a few familiar arrangements.[140]
Voltaic electricity, as the active force produced by chemical change is
commonly called, in honour of the illustrious Volta, is now to be
considered. It differs from frictional electricity in this:—the electricity

developed by friction of the glass plate or cylinder of the electrical machine
is a discharge with a sort of explosion. It is electricity suddenly liberated
from the highest state of tension, whereas that which is generated by
chemical action in the voltaic battery is a steady flowing current. We may
compare one to the ignition of a mass of gunpowder at once, and the other
to the slow burning of the same quantity spread out into a very prolonged
train.
There are numerous ways in which we may excite the phenomena of
Voltaism, but in all of them the decomposition of one of the elements
employed appears to be necessary. This is the case in the arrangements of
batteries in which two dissimilar metals, zinc and copper, silver and
platinum, or the like, is immersed in fluids; the zinc or the silver are
gradually converted into soluble salts, which are dissolved, whilst the
copper or platinum is protected from any action. The most simple manner
of illustrating the development of this electricity is by placing a piece of
silver on the tongue, and a piece of zinc or lead underneath it. No effect will
be observed so long as the two metals are kept asunder, but when their
edges are brought together, a slight tremulous sensation will pass through
the tongue, a saline taste be distinguished by the palate, and if in the dark,
light will be observed by the eye.
This, the germ of the most remarkable of the sciences, was noticed by
Sulzar, fifty years before Galvani observed the convulsions in the limbs of
frogs, when excited by the action of dissimilar metals; but the former paid
little attention to the phenomenon, and the discovery led to no results.
When Galvani’s observant mind was directed to the remarkable fact that the
mere contact of two dissimilar metals with the moist surface of living
muscles produced convulsions, there was an awakening in the soul of that
philosopher to a great fundamental truth, which was nurtured by him, tried
and tested, and preserved to work its marvels for future ages.
Although the world of science looks back to Volta as the man who gave the
first true interpretation of this discovery, yet the ordinary world will never
disconnect this important branch of physical science from the name of
Galvani, and chemical electricity in all its forms will for ever be known
under the familiar name of Galvanism. And it must not be forgotten, that the

phenomena of the manifestation of electricity, in connection with the
conditions of vitality, are entirely due to Galvani.
Let us examine the phenomena of Galvanism in its most simple phases:—
If we place a live flounder upon a plate of zinc, put a shilling on its back,
and then touch both metals with the ends of a metallic wire, the fish will
exhibit painful convulsions. The zinc becomes oxidized by the separation of
oxygen from the fluid on the surface with which it is in contact, whilst
hydrogen gas is liberated at that surface touched by the other metal. Here
we have, in the first place, a chemical change effected, then a peculiar
muscular disturbance. Each successive combination or decomposition, like
a pulsation, is transmitted along the circuit from one extremity to the other.
How the impulse which is derived from the zinc is transmitted through the
body of the animal, or the tongue, to the silver or copper is the next
consideration.
We can only understand this upon the supposition that a series of impulses
are communicated in the most rapid manner along the connecting line; the
idea of a current, although the term is commonly employed, tends to convey
an imperfect impression to the mind. It would seem rather that a disturbance
throughout the entire circuit is at once set up by a series of vibrations or
impulses communicated from particle to particle, and along the strange net-
work of nerves. One set of chemical elements have a tendency to develope
themselves at that point where vibration is first communicated to the mass
from a better conductor than it is, and another set at the point where it
passes from the body to a better conductor than itself. The cause of this is to
be sought for in the laws which regulate molecular constitution—by which
chemical affinity is disturbed,—and a new attractive force exerted, in
obedience to which the vital energy is itself agitated. We must not, however,
forget that it is probable after all, although not yet susceptible of proof, that
the electricity does nothing more than disturb or quicken the unknown
principles upon which chemical and vital phenomena depend; being,
indeed, a secondary agent.[141]
Notwithstanding our long acquaintance with the phenomena of galvanism,
there are but few who entertain a correct idea of the enormous amount of
electricity which is necessary to the existing conditions of matter. To
Faraday we are indebted for the first clear set of deductions from a series of

inductive researches, which are of the most complete order. He has proved,
by a series of exceedingly conclusive experiments, that if the electrical
power which holds a grain of water in combination, or which causes a grain
of oxygen and hydrogen to unite in the right proportions to form water,
could be collected and thrown into the condition of a voltaic current, it
would be exactly the quantity required to produce the decomposition of that
grain of water, or the liberation of its elements, hydrogen and oxygen.[142]
By direct experiment it has been proved that one equivalent of zinc in a
voltaic arrangement evolves such a quantity of electricity in the form of a
current, as, passing through water, will decompose exactly one equivalent
of that fluid. The law has been thus expressed:—The electricity which
decomposes, and that which is evolved by the decomposition of a certain
quantity of matter, are alike. The equivalent weights of bodies are those
quantities of them which contain equal quantities of electricity; electricity
determining the equivalent number, because it determines the combining
force.[143]
The same elegant and correct experimentalist has shown that zinc and
platinum wires, one-eighteenth of an inch in diameter, and about half an
inch long, dipped into water in which is mixed sulphuric acid so weak that
it is not sensibly sour to the tongue, will evolve more electricity in one-
twentieth of a minute than is given by thirty turns of a large and powerful
plate electrical machine in full action, a quantity which, if passed through
the head of a cat, is sufficient to kill it as by a flash of lightning. Pursuing
this interesting inquiry yet further, it is found that a single grain of water
contains as much electricity as could be accumulated in 800,000 Leyden
jars, each requiring thirty turns of the large machine of the Royal Institution
to charge it,—a quantity equal to that which is developed from a charged
thunder-cloud. “Yet we have it under perfect command,—can evolve,
direct, and employ it at pleasure; and when it has performed its full work of
electrolisation, it has only separated the elements of a single grain of
water.”
It has been argued by many that the realities of science will not admit of
anything like a poetic view without degrading its high office; that poetry,
being the imaginative side of nature, has nothing in common with the facts
of experimental research, or with the philosophy which generalises the
discoveries of severe induction. If our science was perfect, and laid bare to

our senses all the secrets of the inner world; if our philosophy was
infallible, and always connected one fact with another through a long series
up to the undoubted cause of all—then poetry, in the sense we now use the
term, would have little business with the truth; it would, indeed, be lost or
embodied, like the stars of heaven, in the brightness of a meridian sun. But
to take our present fact as an example, how important a foundation does it
offer upon which to build a series of thoughts, capable of lifting the human
mind above the materialities by which it is surrounded,—of exalting each
common nature by the refinement of its fresh ideas to a point higher in the
scale of intelligence,—of quickening every impulse of the soul,—and of
giving to mankind the most holy longings.
What does science tell us of the drop of water? Two gases, the one exciting
life and quickening combustion, the other a highly inflammable air, are, by
the influence of a combination of powers, brought into a liquid globe. We
can, from this crystal sphere, evoke heat, light, electricity, and actinism in
enormous quantities; and beyond these we can see powers or forces, for
which, in the poverty of our ideas and our words, we have not names; and
we learn that each one of these principles is engaged in maintaining the
conditions of the drop of water which refreshes organic nature, and gives
gladness to man’s dwelling-place.
Has poetry a nobler theme than this? Agencies are seen like winged spirits
of infinite power, each one working in its own peculiar way, and all to a
common end,—to produce, under the guidance of omnipotent rule, the
waters of the rivers and the seas. As the great ocean mirrors the bright
heaven which overspreads it, and reflects back the sunlight and the sheen of
the midnight stars in grandeur and loveliness; so every drop of water,
viewed with the knowledge which science has given to us, sends back to the
mind reflections of yet distant truths which, rightly followed, will lead us
upwards and onwards in the tract of higher intelligences,—

“To the abodes where the eternals are.”

In the discoveries connected with electricity, we have results of a more
tangible character than are as yet connected with the other physical forces;
and it does appear that this science has advanced our knowledge of nature

and of the mysteries of creation far more extensively than any other
department of purely experimental inquiry.
The phenomena of electro-chemical action are so strange that we must
return for a moment to the consideration of the decomposition of water, and
the appearance of hydrogen at one pole, and of oxygen at the other. It
appears that some confusion of our ideas has arisen from the views which
have been received of the atomic constitution of bodies. We have been
accustomed to regard water,—to take that body as an example of all,—as a
compound of two gases, hydrogen and oxygen; an equivalent, or one atom
of the first, united to an equivalent or one atom of the last, forming one
atom of water. This atom of water we regard as infinitely small;
consequently a drop of water is made up of many hundreds of these
combined atoms, and a pint of water of not less than 10,000 drops. Now, if
this pint of water is connected with the wires of a galvanic battery, although
their extremities may be some inches apart, for every atom of oxygen
liberated at one pole, an atom of hydrogen is set free at the other. It has
been thought that an atom has undergone decomposition at one point, its
oxygen being torn from it, and then there has arisen the difficulty of sending
the atom of hydrogen through all the combined atoms of water across to the
other pole. A series of decompositions and recompositions have been
supposed to take place, and the communication of effects from particle to
particle.
An attracting power for one class of bodies has been found in one pole,
which is repellent to another class; and the reverse order has been detected
at the opposite pole of a galvanic arrangement.[144] That is, the wire which
carries the current from an excited zinc plate has a relation to all bodies,
which is directly opposite to that which is exhibited by the wire conveying
the current from, or completing the circuit with, the copper plate. The one,
for instance, collects and carries acids and the like, the other the metallic
bases. At the extremity of one galvanic wire, placed into a drop of water,
oxygen is always liberated; and at the end of the other, necessary to
complete the circuit with the battery, hydrogen is set free.
It appears necessary, to a clear understanding of what takes place in this
experiment, that we should regard each mass, howsoever large, as the
representative of a single atom. Nor is this difficult, as the following
illustration will show.

Let us take one particle of common salt (chloride of sodium) weighing less
than a grain, and put it into a hundred thousand grains of distilled water. In
a few minutes the salt has diffused itself through the whole of the fluid, and
in every drop we can detect chlorine and soda. We cannot believe that this
grain of salt has split itself up into a hundred thousand parts; we conceive
rather that the phenomenon of solution is one of diffusion. One infinitely
elastic body has interpenetrated with another.
Instead of an experiment with a pint of water, let us take our stand on Dover
heights, and, with a gigantic battery at our command, place one wire into
the ocean on our own shores, and convey the other through the air across
the channel, and let its extremity dip into the sea off Calais pier—the
experiment is a practicable one—we have now an electrical circuit of which
the British channel forms a part, and the result will be exactly the same as
that which we may observe in a watch-glass with a drop of water.
We cannot suppose that the instantaneous and simultaneous effect which
takes place in the water at Calais and at Dover, is due to anything like what
we have studied under the name of convection, when considering Heat.
A thousand balls are placed in a line touching each other; the first ball
receives a blow, and the last ball flies off with a force exactly equal to the
power applied to the first; none of the intermediate balls being moved.
We cannot conceive that the particle A excites the particle B next it, and so
on through the series between the two shores; but regarding the channel as
one large drop, charged with the electric principle as we know it to be, it is
excited by undulation or tremor throughout its width, and we have an
equivalent of oxygen thrown off on one side of the line, and an exact
equivalent of hydrogen at the other, the electro-chemical influence being
exerted only where the current or motion is transferred from one medium to
another.[145] The imperfect character of this view is freely admitted; no
other, consistent with known facts, presents itself by which the effect can be
explained. The fact stands as a truth; the hypothesis by which it is attempted
to be interpreted is open to doubt, and it is opposed to some favourite
theories.
Before we pass to the consideration of the other sources of electricity, it is
important we should understand that no chemical or physical change,
however slight it may be, can occur without the development of electrical

power. If we dissolve a salt in water, if we mix two fluids together, if we
condense a gas, or convert a fluid into vapour, electricity is disturbed, and
may be made manifest to our senses.[146]
It has been shown that this power may be excited by friction (machine
electricity) and by chemical action (voltaic electricity, galvanism); it now
remains to speak of the electricity developed by heat (thermo-electricity),
the electricity exhibited under nervous excitement by the gymnotus and
torpedo (animal electricity); magnetism and its phenomena being reserved
for a separate consideration.
If a bar of metal is warmed at one end and kept cool at the other, an
electrical current circulates through the bar, and may be carried off by
connection with any good conductor, and shown to exhibit the properties of
ordinary electricity. The metals best suited for showing the effects of
thermo-electricity appear to be bismuth and antimony. By binding two bars
of these metals together at one end, and connecting the other ends with a
galvanometer, it will be discovered that an electric current passes off
through the instrument by the slightest variation of temperature. Merely
clasping the two metals, where bound together, with the finger and thumb,
is sufficient to exhibit the phenomenon. By a series of such arrangements,
—which form what have been called thermo-electric multipliers,—we
obtain the most delicate measurers of heat with which philosophers are
acquainted, by the aid of which Melloni has been enabled to pursue his
beautiful researches on radiant caloric.
That this electricity is identical with the other forms has been proved by
employing the current thus excited for the purpose of producing chemical
decomposition, magnetism, and electric light.[147]
The phenomenon of thermo-electricity—the discovery of Seebeck, is
another proof of the very close connection of the physical forces. We
witness their being resolved as it were into each other, electricity producing
heat, and heat again electricity; and it is from these curious results that the
arguments in favour of their intimate relations and actual identity have been
drawn. It will, however, be found to be the best philosophy to regard these
forces as dissimilar, until we are enabled to prove them to be only modified
forms of one principle or power. At the same time it must not be forgotten
that in natural operations we invariably find the combined action of several

forces producing a single phenomenon. The important fact to be particularly
regarded is, that we have evidence that every substance which is unequally
heated becomes the source of this very remarkable form of electricity.[148]
There exist a few fishes gifted with the very extraordinary power of
producing electrical phenomena by an effort of muscular or nervous energy.
The Gymnotus electricus, or electrical eel, and the Raia torpedo, a species
of ray, are the most remarkable. This power is, it would appear, given to
these curious creatures for purposes of defence, and also for enabling them
to secure their prey. The Gymnotus of the South America rivers, will, it is
said, when in full vigour, send forth a discharge of electricity sufficiently
powerful to knock down a man, or to stun a horse; while it can destroy
fishes, through a considerable space, by exerting its strange artillery.[149]
Faraday’s description of a Gymnotus, paralyzing and seizing its prey, is too
graphic and important to be omitted.
“The Gymnotus can stun and kill fish which are in very various positions to
its own body; but on one day, when I saw it eat, its action seemed to me to
be peculiar. A live fish, about five inches in length, caught not half a minute
before, was dropped into the tub. The Gymnotus instantly turned round in
such a manner as to form a coil, inclosing the fish, the latter representing a
diameter across it; a shock passed, and there, in an instant, was the fish
struck motionless, as if by lightning, in the midst of the waters, its side
floating to the light. The Gymnotus made a turn or two to look for its prey,
which, having found, he bolted, and then went about searching for more. A
second smaller fish was given him, which being hurt in the conveyance,
showed but little signs of life, and this he swallowed at once, apparently
without shocking it. The coiling of the Gymnotus round its prey had, in this
case, every appearance of being intentional on its part, to increase the force
of the shock, and the action is evidently well suited for that purpose, being
in full accordance with the well-known laws of the discharge of currents in
masses of conducting matter; and though the fish may not always put this
artifice in practice, it is very probable he is aware of its advantages, and
may resort to it in cases of need.”[150]
Animal electricity has been proved to be of the same character as that
derived from other sources. The shock and the spark are like those of the

machine; and the current from the animal, circulating around soft iron, like
galvanic electricity, has the property of rendering it magnetic.
It is important that we should now review these conditions of electrical
force in connexion with the great physical phenomena of nature.
It is sufficiently evident, from the results which have been examined, that
all matter, whatever may be its form or condition, is for ever under the
operation of the physical forces, in a state of disturbance. From the centre to
the surface all is in an active condition: a state of mutation prevails with
every created thing; and science clearly shows that influences are constantly
in action which prevent the possibility of absolute repose.
Under the excitement of the several agencies of the solar beams, motion is
given to all bodies by the circulation of heat, and a full flow of electricity is
sent around the earth to perform its wondrous works. The solar influences,
which regulate, and possibly determine, every physical force with which we
are acquainted, are active in effecting an actual change of state in matter.
The sunbeam of the morning falls on the solid earth, and its influence is felt
to the very centre. The mountain-top catches the first ray of light, and its
base, still wrapt in mists and darkness, is disturbed by the irradiating power.
The crystalline gems, hidden in the darkness of the solid rock, are
dependent, for that form which makes them valued by the proud and gay, on
the influence of those radiations which they are one day to refract in beauty.
The metals locked in the chasms of the rifted rocks are, for all their physical
peculiarities, as dependent on solar influence as is the flower which lifts its
head to the morning sun, or the bird which sings “at heaven’s high gate.”
Let us, then, examine how far electricity, as distinguished from the other
powers, acts in producing any of these effects.
We find electricity in the atmosphere, which the electrical kite of Dr.
Franklin proved to be identical with that principle produced by the friction
of glass. In the grandeur and terror of a thunderstorm, many see nothing but
manifestations of Almighty wrath. When the volleys of the bursting cloud
are piercing the disturbed air, and the thunders of the discharge are pealing
their dreadful notes above our heads, the chemical combinations of the
noxious exhalations arising from the putrefying animal and vegetable
masses of this earth are effected, elements fitted for the purposes of health
and vegetation are formed, and brought to the ground in the heavy rains

which usually follow these storms. Science has taught man this—has shown
him that the “partial evil” arising from the “winged bolt” is a “universal
good;” and, more than this, it has armed him with the means of protecting
his life and property from the influence of lightnings. So that, like Ajax, he
can defy the storm. By metallic rods, carried up a chimney, a tower, or a
mast, we may form a channel through which the whole of the electricity of
the most terrific thunder-cloud may be carried harmlessly into the earth or
the sea; and it is pleasing to observe that at length prejudice has been
overcome, and “conductors” are generally attached to high buildings, and to
most of the ships of our navy.[151] It was discovered that the devastating
hailstorms of the south of France and Switzerland, so destructive to the
vineyards and crops, were accompanied by evidences of great electrical
excitation, and it was proposed to discharge the electricity from the air by
means of pointed metallic rods. These have been adopted, and, it is said,
with real advantage—each rod protecting an area of one hundred yards.
Thus it is that science ministers to our service; and how much more
pleasing is it to contemplate the lightning, with the philosopher, as an agent
destroying the elements of pestilence, and restoring the healthfulness of the
air we breathe, than with the romancer, to see in it only the dreaded aspect
of a demon of destruction.
The laws which regulate the spread of a pestilence are unknown. The
difficulties of the investigation are great, but they are by no means
insurmountable. A plague passes from the east to the west across the world
—it spreads mourning over the gayest cities, and sorrow sitteth in the
streets. The black death rises in the Orient: it goes on in unchecked strength,
and only finishes its course when it has made the circuit of the civilized
world. The cholera spreads its ebon wings—mankind trembles—watches its
progress, and looks upon the path which is marked by the myriads of the
dead, who have fallen before the dire fiend. The diseases pass away—the
dead are buried, and all is forgotten. The rush and the riot of life are
pursued: and until man is threatened with another advent, he cares not to
trouble himself. Accompanying the last visitation, there appear certain
peculiar meteorological conditions, which point a line of inquiry. It may or
may not be the path which leads to the truth, but certainly its indications are
worthy of careful examination. It may be asked, can weak man stop a
pestilence; can a mortal’s puny hand retard the afflictions of the Almighty?
The question asked—it must be answered in reverence, yet without fear. No

human power can produce a change in the physical conditions of the earth,
or of the air; and if our diseases are connected with those changes, as
beyond all doubt a number of them are, they lie above man’s control. But
when there are indications that causes secondary to these are producing
some dire effect, and when we know that these secondary causes may be
modified, it is sufficient evidence to prove that man is permitted to control
thus far the afflictions which are sent to try his powers.
We find a disease winging its way from lane to alley and closed court,
sweeping with destructive violence its way through damp cellars and
crowded attics; it is rife with mischief along the banks of reeking ditches,
and on the borders of filthy streams. Certain it is, therefore, that some
ultimate connexion exists between the conditions of dirt and this speedy
death. Can science tell of these? has it yet searched out the connecting link?
Let the question be answered by a few facts.
When the cholera first made its appearance, and subsequently, it has been
observed that the electrical intensity of the atmosphere was unusually low.
The disease has departed, and it is then found that the electricity of the air
has been restored to its ordinary condition.
This appears to show some connexion; but how do these conditions link this
physical force with the ditch-seeking disease?
From all stagnant places, from all the sinks of overcrowded humanity, from
fermenting vegetable and from putrefying animal matter, there are
constantly arising poisonous exhalations to do their work of destruction.
Where death and decay is a law, this must of necessity constantly occur; but
the poisonous reek may be diffused, or it may be concentrated, and Nature
has provided for this, and ordered the means for rendering the poison
harmless.
By the agency of electricity,—probably, too, by the influence of light,—the
oxygen in the air undergoes a peculiar change, by which it is rendered far
more energetic than it is in its ordinary state. This is the condition to which
the name of ozone has been applied. Now, this ozone, or this peculiar
oxygen, always exists in the air we breathe; but its quantity is subject to
great and rapid variations. It is found that when electrical intensity is high

the quantity of this principle is great; when the electrical intensity is low, as
in the cholera years, the proportion of ozone is relatively low.
This remarkable chemical agent possesses the power of instantly combining
with organic matter,—of removing with singular rapidity all noxious
odours; and it would appear to be the most active of all known
disinfectants.
May we not infer from the facts stated that the pestilence we dread is the
result of organic poison, which from a deficiency of ozone,—its natural
antidote,—exerts its baneful influences on humanity. This deficiency is due
to alterations in the electrical character of the air, possibly dependent upon
phenomena taking place in the sun itself, or it may be still more directly
influenced by variations in the character of solar light, which we have not
yet detected, by which the conditions of the electric power are determined.
This may be a line along which it is fair to push enquiry. But such an
enquiry must be made in all the purity of the highest inductive philosophy,
and speculation must be held firmly in the controlling chains of experiment
and observation. In the truths, however, which are known to us, there is so
much harmony and consistence that even the melancholy theme links itself
—a tragedy—with the Poetry of Science.
It has been thought, and much satisfactory evidence has been brought
forward to support the idea, that the earth’s magnetism is due to currents of
electricity circulating around the globe; as a great natural current from east
to west—that, indeed, it has an unvarying reference to the motion of the
earth in relation to the sun.[152]
These terrestrial currents, as they have without doubt a very important
bearing on the structural conditions of the rock-formations and the
distribution of minerals, require an attentive consideration; but we must, in
the first place, examine, as far as we know, the influences exerted, or
supposed to be exerted, by electricity, in its varied forms.
The phenomena of vitality have, by many, been considered as immediately
dependent upon its influence; and a rather extensive series of experiments
has been made in support of this hypothesis. The researches of Philip on the
action of the organs of digestion, when separated from their connection with
the brain, but united with a galvanic battery, have been proved by Dr. Reid

to be delusive;[153] since, as the organ is not removed from the influence of
the living principle, it is quite evident that the electricity here is only
secondary to some more important power. Matteucci has endeavoured to
show that nervous action is intimately connected with electric excitation,
and that electricity may be made a measurer of nervous irritability.[154]
There can be no doubt that a peculiar susceptibility to excitement exists in
some systems, and this is very strikingly shown in the disturbances
produced by electric action; but in the experiments which have been
brought forward we have only the evidence that a certain number of
muscular contractions are exhibited in one animal by a current of electricity,
giving a measured effect by the voltameter, which are different from those
produced upon another by a current of the same power. An attempt has
recently been made by Mr. A. Smee to reduce the electrical phenomena
connected with vitality to a more exact system than had hitherto been done.
We cannot, however, regard the attempt as successful. The author has
trusted almost entirely to analogical reasoning, which is in science always
dangerous.[155] In the development of electricity during the operation of the
vital force, we see only the phenomena produced by the action of any two
dissimilar chemical compounds upon each other. It has been thought that
the structure of the brain presents an analogy to that of the galvanic battery,
and the nerves represent the conducting wires. Although, however, some of
the conditions appear similar, there are many which have no representatives
in either the mechanical structure or the physical properties of the brain, so
far as we know it. That the brain is the centre, the source, and termination of
sensation is very clearly proved by physiological investigations. That the
nerves are the media by which all sensation is conveyed to the brain, and
also the instruments by which the will exerts its power over the muscles, is
equally well established. But to say that we have any evidence to support
the idea that electricity has aught to do directly with these great
physiological phenomena, would be a bold assertion, betraying a want of
due caution on the part of the investigator. That electric effects are
developed during the operations of vitality is most certain. Such must be the
case, from the chemical changes taking place during respiration and
digestion, and the mechanical movements by which, even during external
repose, the necessary functions of the body are carried on. Whether
electricity is the cause of these, or an effect arising from them, we need not
stop to examine, as this is, in the present state of our knowledge, a mere

speculation. We have no evidence that electricity is an exciting power, but
rather that it is one of those forces which tend to establish the equilibrium
of matter. When disturbed—when its equilibrium is overset—it does, in its
efforts to regain its stability, produce most remarkable effects. An electrical
machine must be rubbed to exhibit any force. In all galvanic arrangements,
even the most simple, dissimilar bodies are brought together, and the latent
electricity of both is disturbed; and, even in the magnet, it is only when this
takes place that its electrical powers are developed. In the Gymnotus,
electricity appears to be dependent upon the power of the will of the animal;
but even in this extraordinary fish, it is only under peculiar conditions that
the electrical excitement takes place, and “what they inflict, they feel”
during the restoration of that equilibrium which is necessary to their healthy
state. In every case, therefore, we see that some power far superior to this is
the ultimate cause; indeed, light and heat, and probably actinism, appear to
stand superior to this principle; and on these, in some combined mode of
action, in all probability, sensible electricity is dependent. Beyond even
these elements, largely as they are engaged in the organic and inorganic
changes of this world, there are occult powers which may never be
understood by finite beings. We advance step by step from the most solid to
the most ethereal of material creations, and we examine a series of
extraordinary effects produced by powers which we know not whether to
regard as material or immaterial, so subtile are they. On these, it appears,
we may exhaust our inductive investigations—we may discover the laws by
which these principles act upon the grosser elements, and develope
phenomena of a very remarkable kind which have been unobserved or
misunderstood. Whether light, heat, and electricity are modifications of one
power, or different powers very closely united in action, is a problem we
may possibly solve; but to know what they are, appears to be beyond the
hopes of science; and it were idle to dream of elucidating the causes hidden
beyond these forces, and by which they are regulated in all their actions on
dead or living matter.
M. Du Bois Raymond, from a series of researches remarkable alike for their
difficulty and the delicacy with which they have been pursued, draws the
following, amongst many others, as his conclusions as to the connection of
electricity and vital phenomena.

The muscles and nerves, including the brain and the spinal chord, are
endowed during life with an electromotive power, which acts according to a
definite law.
The electromotive power lasts after death, or in dissected nerves and
muscles after separation from the body of the animal, as long as the
excitability of the nervous and muscular fibre; whether these fibres are
permitted to die gradually from the cessation of the conditions necessary to
the support of life, or whether they are suddenly deprived of their vital
properties by heat or chemical action.
Let us not suppose for a moment that these conclusions indicate in the
remotest degree that electricity is life,—that vital power is due to electricity.
During life, with every motion, and, indeed, with every emotion, whether
we move a muscle or exert the mind, there is a change of state. The result of
this is chemical phenomena,—heat and electricity; but these are not life. We
excite them equally by giving motion to a dead mass.
Notwithstanding the assertions of those who have zealously followed the
path of Mesmer, and examined, or they have thought so, the psychological
effects dependent upon some strange physiological conditions, there is not
an experiment on record,—there is not an observation worthy of credit,
which shows that electricity has any connection with their results. All
around their subject is uncertainty: doubt involves every experiment, and
deception clouds a large number. Some few grains of truth, and these are
sufficiently strange, are mixed up in an enormous mass of error.
All the phenomena of life,—of the vis vitæ or vitality, are beyond human
search. All the physical forces, or elements, we may examine by the test of
experiment: but the principle on which sensation depends, the principle
even upon which vegetable life depends, cannot be tested. Life is infinitely
superior to every physical force; it holds them all in control, but is not itself
controlled by them; it keeps its state sacred from human search,—the
invisible hidden behind the veil of mortality.
During changes in the electrical conditions of the earth and atmosphere,
vegetables give indications of being in a peculiar manner influenced by this
power. It is proved by experiments that the leaves of plants are among the
best conductors of electricity, and it has hence been inferred that it must

necessarily be advantageous to vegetation. That vegetable growth is,
equally with animal growth, subject to electricity, as one of its quickening
powers, must be admitted; but all experiments which have been fairly tried
with the view of stimulating the growth of plants by its agency, have given
results of a negative character.[156] That a galvanic arrangement may
produce chemical changes in the soil, which may be advantageous to the
plant, is probable; but that a plant can be brought to maturity sooner, or be
made to develope itself more completely, under the direct action of
electrical excitation, appears to be one of those dreams of science which
will have a place amongst the marvels of alchemy and the fictions of
astrology. An attentive examination of all the conditions necessary for the
satisfactory development of the plant, will render it evident, that although
the ordinary electrical state of the earth and atmosphere must influence the
processes of germination and vegetable growth, yet that any additional
excitement must be destructive to them. The wonders wrought by electrical
power are marvellous; a magic influence is exerted by it, and naturally the
inquiring mind is led at first to believe that electricity is the all-powerful
principle of creation; but a little reflection will serve to convince us that it is
a subordinate agent, although a powerful one.
In proceeding with our examination of the phenomena which present
themselves in connection with the terrestrial currents, we purposely
separate magnetism from those more distinct electro-chemical agencies
which play so important a part in the great cosmical operations.
Electricity, we have already stated, flows through or involves all bodies;
but, like heat, it appears to undergo a very remarkable change in becoming
associated with some forms of matter. We have the phenomena of
magnetism when an electric current circulates through a metallic wire, and
it would appear that all other bodies acquire a peculiar polar condition
under the influence of this principle, which will be explained in the next
chapter.
The rocks, taken as masses, will not conduct an electric current when dry:
granite, porphyry, slate, and limestone, obstructing its passage even through
the smallest spaces. But all the metallic formations admit of its circulating
with great freedom. This fact it must, however, be remembered does not in
any way interfere with the hypothesis of the existence of electricity in all
bodies, in what we must regard as its latent state, from which, under

prescribed conditions, it may be readily liberated. Neither does it affect the
question of circulation, in relation to the great diffusion of electricity which
we suppose to exist through all nature, and to move in obedience to some
fixed law. We know that through the superficial strata electric currents
circulate freely, whether they are composed of clay, sand, or any mixture of
these with decomposed organic matter; indeed, that with any substance in a
moist state they suffer no interruption.
The electricity of mineral veins has attracted much attention, and numerous
investigations into the phenomena which these metalliferous formations
present, have been made from time to time.[157]
By inserting into the mass of a copper lode, or vein, in situ, a metallic wire,
which shall be connected with a measurer of galvanic action, a wire also
from the instrument being brought into contact with another lode, an
immediate effect is generally produced, showing that a current is traversing
through the wires from one lode to the other, and completing the circulation
probably over the dark face of the rock in which the fissures forming the
mineral veins exist.[158] The currents thus detected are often sufficiently
active to deflect a magnetic needle powerfully, to produce, slowly, electro-
chemical decomposition, and to render a bar of iron magnetic. These
currents must not be confounded with the great electrical movements
around the earth. They are only to be detected in those mineral formations
in which there is evidence of chemical action going on, and, the greater the
amount of this chemical operation, the more energetic are the electrical
currents.[159] We have, however, very good evidence that these local
currents have, of themselves, many peculiar influences. It not unfrequently
happens that owing to some great disturbance of the crust of the earth, a
mineral vein is dislocated, and one part either sinks below, or is lifted above
its original position; the fissures formed between the two being usually
filled in with clay or with crystalline masses of more recent formation than
the fissure itself. It is frequently found that these “cross courses,” as they
are called in mining language, contain ores of a different character from
those which constitute the mineral vein; for instance, in them nickel, cobalt,
and silver are not unfrequently discovered. When these metals are so found,
they almost invariably occur between the ends of the dislocated lode, and
often take a curvilinear direction, as if they were deposited along a line of
electrical force.[160]

In the laboratory such an arrangement has been imitated, and in a mass of
clay fixed between the galvanic plates, after a short period a distinct
formation of a mineral vein has taken place.[161] By the action, too, of weak
electrical currents, Becquerel, Crosse, and others, have been successful in
imitating nature so far as to produce crystals of quartz and other minerals.
In addition to this evidence, in support of the electrical theory of the origin
of mineral veins, it can be experimentally shown that a schistose structure
may be given to clays and sandstone by voltaic action.[162]
There is often a very remarkable regularity in the direction of mineral veins:
throughout Cornwall, for instance, they most commonly have a bearing
from the E. of N. to the W. of S. It has hence been inferred that they observe
some relation to the magnetic poles of the earth. However this may be, it is
certain that the ore in any lodes which are in a direction at right angles, or
nearly so, to this main line, differs in character from that found in these, so
called, east and west lobes.[163]
The sources of chemical action in the earth are numerous. Water percolating
through the soil, and finding its way to great depths through fissures in the
rocks, carries with it oxygen and various salts in solution. Water again
rising from below, whether infiltrated from the ocean or derived from other
sources, is usually of a high temperature, and it always contains a large
quantity of saline matter.[164] By these causes alone chemical action must be
set up. Chemical change cannot take place without a development of
electricity: and it has been proved that the quantity of electricity required
for the production of any change is equal to that contained in the substances
undergoing such change. Thus a constant activity is maintained within the
caverns of the rock by the agency of the chemical and electrical elements,
and mutations on a scale of great grandeur are constantly taking place under
some directive force.
The mysterious gnome, labouring—ever labouring—in the formation of
metals, and the mischievous Cobalus of the mine, are the poor creations of
superstition. A vague fear is spread amongst great masses of mankind
relative to the condition of the dark recesses of the earth; a certain
unacknowledged awe is experienced by many on entering a cavern, or
descending a mine: not the natural fear arising from the peculiarity of the
situation, but the result of a superstitious dread, the effect of a depraved

education, by which they have been taught to refer everything a little
beyond their immediate comprehension to supernatural causes. The spirit of
demon worship, as well as that of hero worship, has passed from the early
ages down to the present; and under its influence the genii of the East and
the demons of the West have preserved their traditionary powers.
Fiction has employed itself with the utmost license in giving glowing
pictures of treasures hidden in the earth’s recesses. The caverns of
Chilminar, the cave of Aladdin, the abodes of the spirits of the Hartz, and
the dwellings of the fairies of England, are gem-bespangled and gold-
glistening vaults, to which man has never reached. The pictures are
pleasing; but although they have the elements of poetry in them, and delight
the young mind, they want the sterling character of scientific truth; and the
wonderful researches of the plodding mineralogist have developed more
beauty in the caverns of the dark rock than ever fancy painted in her
happiest moments.
In all probability the action of the sun’s rays upon the earth’s surface,
producing a constantly varying difference of temperature, and also the
temperature which has been observed as existing at great depths, give rise
to thermo-electrical currents, which may play an important part in the
results thus briefly described.
In connection with these great natural operations, explaining them, and
being also, to some extent, explained by them, we have the very beautiful
application of electricity to the deposition of metals, called the Electrotype.
Applying the views we have adopted to this beautiful discovery,[165] the
whole process by which these metallic deposits are produced will be yet
more clearly understood. By the agency of the electric fluid, liberated in the
galvanic battery, a disturbance of the electricity of the solution of copper,
silver, or gold, is produced, and the metal is deposited; but, instead of
allowing the acid in combination to escape, it has presented to it some of
the same metal as that revived, and, consequently, it combines with it, and
this compound, being dissolved, maintains the strength of the solution.[166]
A system of revival, or decomposition, is carried on at one pole, and one of
abrasion, or more correctly speaking, of composition and solution, at the
other. By taking advantage of this very extraordinary power of electricity,
we now form vessels for ornament or use, we gild or silver all kinds of

utensils, and give the imperishability of metal to the most delicate
productions of nature—her fruits, her flowers, and her insects;—and over
the finest labours of the loom we may throw coatings of gold or silver to
add to their elegance and durability. Nor need we employ the somewhat
complex arrangement of the battery: we may take the steel magnet, and, by
mechanically disturbing the electricity it contains, we can produce a current
through copper wires, which may be used, and is extensively employed, for
gilding and silvering.[167] The earth itself may be made the battery, and, by
connecting wires with its mineral deposits, currents of electricity have been
secured, and used for the production of electrotype deposit.[168]
The electrotype is but one of the applications of electricity to the uses of
man. This agent has been employed as the carrier of thought; and with
infinite rapidity, messages of importance, communications involving life,
and intelligences outstripping the speed of coward crime, have been
communicated. There will be no difficulty in understanding the principle of
this, although many of the nice mechanical arrangements, to ensure
precision, are of a somewhat elaborate character. The entire action depends
on the deflection of a compass-needle by the passage of an electric current
along its length. If at a given point we place a galvanic battery, and at
twenty or one hundred miles distance from it a compass-needle, between a
wire brought from, and another returning to the battery, the needle will
remain true to its polar direction so long as the wires are unexcited; but the
moment connection is made, and the circuit is complete, the electricity of
the whole extent of wire is disturbed, and the needle is thrown at right
angles to the direction of the current. Provided a connection between two
points can be secured, however remote they are from each other, we thus,
almost instantaneously, convey any intelligence. The effects of an electric
current would appear at a distance of 576,000 miles in a second of time; and
to that distance, and with that speed, it is possible, by Professor
Wheatstone’s beautiful arrangements, to convey whispers of love or
messages of destruction.
The enchanted horse of the Arabian magician, the magic carpet of the
German sorcerer, were poor contrivances, compared with the copper wires
of the electrician, by which all the difficulties of time and the barriers of
space appear to be overcome. In the Scandinavian mythology we find
certain spiritual powers of evil enabled to pass with imperceptible speed

from one remote point to another, sowing the seeds of a common ruin
amongst mankind. Such is the morbid creation of a wild yet highly
endowed imagination. The spirit of evil diffuses itself in a remarkable
manner, and, indeed, we might almost assign to it the power of ubiquity; but
in reality its advance is progressive, and time enters as an element into any
calculation on its diffusion. Electricity is instantaneous in action; as a spirit
of peace and good-will it can overtake the spirit of evil, and divert it from
its designs. May we not hope that the electrical telegraph, making, as it
must do, the whole of the civilized world enter into a communion of
thought, and, through thought, of feeling with each other, will bind us up in
one common brotherhood, and that, instead of misunderstanding and of
misinterpreting the desires and the designs of each other, we shall learn to
know that such things as “natural enemies” do not exist? To hope to break
down the great barrier of language is perhaps too much; but assuredly we
may hope that, as we must do when closer and more intimate relations are
secured by the aids of science, the barrier of prejudice may be razed to the
ground, and not one stone left to stand upon another? Our contentions, our
sanguinary wars, consecrated to history by the baptism of blood, have in
every, or in nearly every, instance sprung from the force of prejudice, or the
mistakes of politicians, whose minds were narrowed to the limits of a
convention formed for perpetuating the reign of ignorance.
And can anything be more in accordance with the spirit of all that we revere
as holy, than the idea that the elements employed by the All Infinite in the
works of physical creation shall be made, even in the hands of man, the
ministering angels to the great moral redemption of the world? Associate
the distant nations of the earth, and they will find some common ground on
which they may unite. Mortality compels a dependence; and there are
charities which spring up alike in the breast of the savage and the civilized
man, which will not be controlled by the cold usages of pride, but which,
like all truths, though in a still small voice, speak more forcibly to the heart
than errors can, and serve as links in the great chain which must bind
mankind in a common brotherhood. “None are all evil,” and the best have
much to learn of the amenities of life from him who yet lives in a “state of
nature,” or rather from him whose sensualities have prevailed over his
intellectual powers, but who still preserves many of the noblest instincts, to
give them no higher term, which other races, proud of their intelligence,
have thrown aside. Time and space have hitherto prevented the

accomplishment of this; electricity and mechanics promise to subdue both;
and we have every reason to hope those powers are destined to accelerate
the union of the vast human family.
Electrical power has also been employed for the purpose of measuring time,
and by its means a great number of clocks can be kept in a state of uniform
correctness, which no other arrangement can effect. A battery being united
with the chief clock, which is itself connected by wires with any number of
clocks arranged at a distance from each other, has the current continually
and regularly interrupted by the beating of the pendulum, which
interruption is experienced by all the clocks included in the electric circuit;
and, in accordance with this breaking and making contact, the indicators or
hands move over the dial with a constantly uniform rate. Instead of a
battery the earth itself has supplied the stream of electric fluid, with which
the rate of its revolutions has been registered with the utmost fidelity.[169]
Electricity, which is now employed to register the march of time, rushes far
in advance of the sage who walks with measured tread, watching the falling
sands in the hour-glass.
The earth is spanned and the ocean pierced by the wires of the electric
telegraph. Already, from the banks of the Thames to the shores of the
Adriatic, our electric messenger will do our bidding. The telegraph is
making its way through Italy, and it is dipping its wires in the
Mediterranean, soon to reach the coast of Africa. They will then run along
the African shores to Egypt and Turkey, and still onward until they unite
with the telegraphs of India, of which three thousand miles are in progress.
From Hindostan these wondrous wires will run from island to island in the
Indian Archipelago, and thus connect Australia and New Zealand with
Europe.
In a few years we may expect to have an instantaneous report in London of
the extraordinary “nugget” discovered by some fortunate gold-digger; and
the exile from his native land in the Islands of the South Pacific Ocean, may
learn every hour, if he will, of the doings of his family and friends in some
village home of England.

FOOTNOTES:
[136] Traité de Physique: M. Biot, vol. vii. Becquerel: Annales de Chimie, vol.
xlvi.-xlix. Faraday’s Experimental Researches in Electricity, 2 vols., 1830–1844.
A Speculation touching Electric Conduction and the Nature of Matter: by
Michael Faraday, D.C.L., F.R.S.; Philosophical Magazine, vol. xxiv., 1836.
Objections to the theories severally of Franklin, Dufay, and Ampère, with an
attempt to explain Electrical Phenomena by statical or undulatory polarization:
by Robert Hare, M.D., Emeritus Professor of Chemistry in the University of
Pennsylvania.
[137] “A good piece of gutta percha will insulate as well as an equal piece of
shell-lac, whether it be in the form of sheet, or rod, or filament; but being tough
and flexible when cold, as well as soft when hot, it will serve better than shell-
lac in many cases where the brittleness of the latter is an inconvenience. Thus it
makes very good handles for carriers of electricity in experiments on induction;
not being liable to fracture in the form of thin band or string, it makes an
excellent insulating suspender; a piece of it in sheet makes a most convenient
insulating basis for anything placed on it. It forms excellent insulating plugs for
the stems of gold-leaf electrometers, when they pass through sheltering tubes,
and larger plugs form good insulating feet for electrical arrangements; cylinders
of it, half an inch or more in diameter, have great stiffness, and form excellent
insulating pillars. In these and in other ways its power as an insulator may be
useful.”—On the use of Gutta Percha in Electrical Insulation: by Dr. Faraday;
Philosoph. Mag., March, 1848.
The following deductions have been given by Faraday, in his Researches in
Electricity, a work of most extraordinary merit, being one of the most perfect
examples of fine inductive philosophy which we possess in the English
language:—
“All bodies conduct electricity in the same manner from metals to lacs and
gases, but in very different degrees.
“Conducting power is in some bodies powerfully increased by heat, and in
others diminished, yet without one perceiving any accompanying essential
electrical difference, either in the bodies, or in the change occasioned by the
electricity conducted.
“A numerous class of bodies insulating electricity of low intensity, when solid,
conduct it very freely when fluid, and are then decomposed by it.
“But there are many fluid bodies which do not sensibly conduct electricity of
this low intensity; there are some which conduct it and are not decomposed; nor
is fluidity essential to decomposition.
“There are but two bodies (sulphuret of silver and fluoride of lead) which,
insulating a voltaic current when solid, and conducting it when fluid, are not
decomposed in the latter case.
“There is no strict electrical distinction of conduction which can as yet be drawn
between bodies supposed to be elementary, and those known to be compounds.”
[138] Faraday’s Speculation on the Nature of Matter, already referred to.

[139] Experimental Researches: by Dr. Faraday. Chemical Decomposition, p.
151.
[140] Karsten; Poggendorff’s Annalen, vol. lvii.
[141] Traité Expérimental de l’Électricité et du Magnétisme: Becquerel, 1834,
Priestley’s Introduction to Electricity. On Electricity in Equilibrium: Dr. Young’s
Lectures.
[142] Faraday’s Experimental Researches on Electricity. This philosopher has
shown, by the most conclusive experiments, “that the electricity which
decomposes, and that which is evolved by the decomposition of, a certain
quantity of matter, are alike. What an enormous quantity of electricity, therefore,
is required for the decomposition of a single grain of water! We have already
seen that it must be in quantity sufficient to sustain a platinum wire 1/104 of an
inch in thickness, red hot, in contact with the air, for three minutes and three
quarters. It would appear that 800,000 charges of a Leyden battery, charged by
thirty turns of a very large and powerful plate machine, in full action—a quantity
sufficient, if passed at once through the head of a rat or cat, to have killed it as
by a flash of lightning—are necessary to supply electricity sufficient to
decompose a single grain of water; or, if I am right, to equal the quantity of
electricity which is naturally associated with the elements of that grain of water,
endowing them with their mutual chemical affinity.”
[143] Experimental Researches: Faraday.
[144] The appearance of acid and alkaline matter, in water acted on by a current
of electricity, at the opposite electrified metallic surfaces, was observed in the
first chemical experiments made with the column of Volta—(see Nicholson’s
Journal, vol. iv. p. 183, and vol. iv. p. 261, for Mr. Cruickshank’s Experiments;
and Annales de Chimie, tom. xxxvii. p. 233, for those of M. Desormes): On
some Chemical Agencies in Electricity: by Sir Humphry Davy.—Philosophical
Transactions for 1807. The various theories of electro-chemical decomposition
are carefully stated by Faraday, in his fifth series of Experimental Researches on
Electricity, in which he thus states his own views:—“It appears to me that the
effect is produced by an internal corpuscular action exerted according to the
direction of the electric current, and that it is due to a force either superadded to
or giving direction to the ordinary chemical affinity of the bodies present. The
body under decomposition may be considered as a mass of acting particles, all
those which are included in the course of the electric current contributing to the
final effect; and it is because the ordinary chemical affinity is relieved,
weakened, or partly neutralized by the influence of the electric current in one
direction parallel to the course of the latter, and strengthened or added to in the
opposite direction, that the combining particles have a tendency to pass in
opposite courses.”
[145] “This capital discovery (chemical decomposition of electricity) appears to
have been made in the first instance by Messrs. Nicholson and Carlisle, who
observed the decomposition of water so produced. It was speedily followed up
by the still more important one of Berzelius and Hisinger, who ascertained it as a
general law, that, in all the decompositions so effected, the acids and oxygen
become transferred and accumulated around the positive, and hydrogen, metals,
and alkalies around the negative, pole of a voltaic circuit; being transferred in an
invisible, and, as it were, a latent or torpid state, by the action of the electric

current, through considerable spaces, and even through large quantities of water
or other liquids, again to reappear with all their properties at their appropriate
resting-places.”—Discourse on the Study of Natural Philosophy: by Sir John
Herschel, Bart., F.R.S.
[146] Numerous beautiful illustrations of this fact will be found in Becquerel’s
Traité Expérimental de l’Électricité et du Magnétisme.
[147] See Le Feu élémentaire of l’Abbé Nollet; Leçons de Physique, tom. vi. p.
252; Du Pouvoir thermo-électrique, by M. Becquerel—Annales de Chimie, vol.
xli. p. 353; also a Memoir by Nobili, Bibliothèque Universelle, vol. xxxvii. p.
15; Experimental Contributions towards the theory of Thermo-Electricity by Mr.
J. Prideaux—Philosophical Magazine, vol. iii., Third Series; On the Thermo-
Magnetism of Homogeneous Bodies, with illustrative experiments, by Mr.
William Sturgeon—Philosophical Magazine, vol. x. p. 1–116, New Series. Botto
made magnets and obtained chemical decomposition. Antinori produced the
spark. Mr. Watkins heated a wire in Harris’s Thermo-Electrometer.
[148] A very ingenious application of the knowledge of this fact was suggested
by Mr. Solly, by which the heat of a furnace could be constantly registered at a
very considerable distance from it. See Description of an Electric Thermometer:
by E. Solly, Jun., Esq. Philosophical Magazine, vol. xx. p. 391. New Series.
[149] Humboldt; Personal Narrative, Chap. xvii.—Annales de Chimie, vol. xiv.
p. 15.
[150] Experimental Researches on Electricity. Series xv. Consult Sir Humphry
Davy: An Account of some Experiments on the Torpedo.—Philosophical
Transactions, 1829, p. 15. John Davy, M.D., F.R.S.: An Account of some
Experiments and Observations on the Torpedo, ibid., 1832, p. 259; and the same
author’s Observations on the Torpedo, with an Account of some Additional
Experiments on its Electricity; and Matteucci, Bibliothèque Universelle, 1837,
vol. xii. p. 174.
[151] On Lightning Conductors, by Sir William Snow Harris; Observations on
the Action of Lightning Conductors, by W. Snow Harris, Esq., F.R.S.—London
Electrical Society’s Transactions. Numerous valuable papers On Electricity, by
Sir William Harris, will be found in the Philosophical Transactions.
[152] Adopting, to a certain extent, this view, Faraday, in his Electrical
Nomenclature, proposed for the word pole to substitute anode (ανω, upwards,
and ὁδος, a way), the way which the sun rises; and cathode (κατα, downwards,
and ὁδος, a way), the way which the sun sets. The hypothesis belongs essentially
to Ampère. Objections to the Theories severally of Franklin, Dufay, and Ampère,
with an Effort to Explain Electrical Phenomena by Statical or Undulatory
Polarisation, by Robert Hare, M.D., Pennsylvania, will well repay an attentive
perusal.
[153] Inquiry into the Laws of the Vital Functions.—Philosophical Transactions,
1815, 1822; Some Observations relating to the Functions of Digestion, ibid.,
1829: On the Powers on which the Functions of Life in the more perfect animals
depend, and on the manner in which they are associated in the production of
their more complicated results, by A. P. W. Philip, M.D., F.R.S., L. and E.—The
following extract from the last-quoted of Dr. Philip’s Memoirs, will give a
general view of the conclusions of that eminent physiologist:—“With respect to

the nature of the powers of the living animal which we have been considering,
the sensorial and muscular powers, and the powers peculiar to living blood, we
have found belong to the living animal alone, all their peculiar properties being
the properties of life. The functions of life may be divided into two classes, those
which are affected by the properties of this principle alone, and those, by far the
most numerous class, which result from the co-operation of these properties with
those of the principles which operate in inanimate nature. The nervous power we
have found to be a modification of one of the latter principles, because it can
exist in other textures than those to which it belongs in the living animal, and we
can substitute for it one of those principles without disturbing the functions of
life.
“Late discoveries have been gradually evincing how far more extensive than was
supposed, even a few years ago, is the dominion of electricity. Magnetism,
chemical affinity, and (I believe from the facts stated in the foregoing paper, it
will be impossible to avoid the conclusion) the nervous influence, the leading
power in the vital functions of the animal frame, properly so called, appear all of
them to be modifications of this apparently universal agent; for I may add we
have already some glimpses of its still more extensive dominion.”
Refer to Dr. Reid’s papers.
[154] Electro-physiological Researches: by Signor Carlo Matteucci; Phil. Trans.
1845, p. 293, and subsequent years.
[155] Electro-Biology: by Alfred Smee, Esq.
[156] Observations of Electric Currents in Vegetable Structures: by Golding
Bird, Esq., F.L.S.; Magazine of Natural History, vol. x. p. 240. In this paper Dr.
Bird remarks that his experiments lead to the conclusion that vegetables cannot
become so charged with electricity as to afford a spark; that electrical currents of
feeble tension are always circulating in vegetable tissues; and that electrical
currents are developed during germination from chemical action.
[157] On Mineral Veins: by Robert Were Fox, Esq.; Fourth Report of the Royal
Cornwall Polytechnic Society. On the Electro-magnetic Properties of
Metalliferous Veins in the mines of Cornwall: by Robert W. Fox, Esq.; Phil.
Trans. 1830, p. 399.
[158] Experiments and Observations on the Electricity of Mineral Veins: by
Robert Hunt and John Phillips; Reports of the Royal Cornwall Polytechnic
Society for 1841–42. On the Electricity of Mineral Veins: by Mr. John Arthur
Phillips; Ibid., 1843.
[159] In the lead lodes of Lagylas and Frongoch, electrical currents were
detected by Mr. Fox, but none in those of South Mold and Milwr, in Flintshire:
Cornwall Geological Transactions, vol. iv. In the lead veins of Coldberry and
Skeers, in Teasdale, Durham, the currents detected were very feeble: Reports of
the Bristol Association, 1838. Von Strombeck could detect no electric currents in
the veins worked in the clay slate near Saint Goar, on the Rhine: Archiv. für
Mineralogie, Geognosie, &c., von Dr. C. J. B Karsten, 1833. Professor Reich,
however, obtained very decided results at Frisch Glück, Neue Hoffnung, Gottlob,
and in other mineral veins in the mining districts of Saxony: Edinburgh New
Philosophical Journal, vol. xxviii. 1839. The irregularities are all to be explained
by the presence or absence of chemical excitation.

[160] This was remarkably the case at Huel Sparnon, near Redruth, where the
cobalt was discovered between two portions of a dislocated lode; and the same
was observed by Mr. Percival Johnson in a small mine worked for nickel, near
St. Austell.
[161] On the process used for obtaining artificial veins in clay: by T. B. Jordan;
Sixth Annual Report of the Royal Cornwall Polytechnic Society. See also my
memoir, already referred to, in the Memoirs of the Geological Survey and
Museum of Practical Geology, vol. i.
[162] See Becquerel, Traité Experimental de l’Electricité, &c. Electrical
Experiments on the formation of Artificial Crystals: by Andrew Crosse, Esq.;
British Association Reports, vol. v., 1836. The lamination of clay and other
substances is described in my memoir referred to, Note p. 226.
[163] Report on the Geology of Cornwall, Devon, and West Somerset, by Sir
Henry T. De la Beche: Theoretical observations on the formation and filling of
Mineral Veins and Common Faults, p. 349.
[164] The following analyses of waters from deep mines were made by me in
1840, and, with many others, published in the Reports of the Royal Cornwall
Polytechnic Society.
Consolidated Mines, Gwennap, Cornwall. In 1,000 grains of water.
Muriate of soda 1·5
Sulphate of lime ·5
Sulphate of iron ·15
Sulphate of copper 1·25
Silica ·15
Alumina ·3
——
Total 3·7

United Mines, Gwennap.
Muriate of soda 1·10
Muriate of lime ·15
Sulphate of soda ·50
Sulphate of lime 1·5
Sulphate of iron ·75
Alumina ·5
Silica ·15
——
Total 4·65

Great St. George.
Muriate of soda 1·35
Sulphate of lime ·74