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.

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.