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Popular Science Monthly/Volume 34/December 1888/Atomic Worlds and their Motions


THIS formidable title will doubtless lead many of my readers to apprehend that I am now going to inflict upon them one of those abstruse and profound disquisitions on molecular physics which are very learned and very incomprehensible. But I do not propose to do anything of the kind. I have no desire to go into mathematics, or to weary them with a more or less tedious recapitulation of the gradual development, from crude beginnings, of our present science of molecular dynamics, by going back to the earliest conceptions of atoms by the Greek philosophers, or even to the time of Dalton and Bernouilli.

I merely desire to explain, in as popular a language as the subject permits, in how far the researches of men like Helmholtz and Sir William Thomson have modified our ideas of the ultimate composition of matter. There will be nothing offered that is absolutely original except certain deductions of my own which, in my opinion, necessarily flow from the assumption that matter is composed of indivisible and indestructible particles. I have reason to believe that these deductions will be received with interest and that they will throw light on and explain many things which may have puzzled those not intimately acquainted with the subject.

It may, indeed, be presumed that a popular exposition of the present state of the science of molecular physics will be appreciated. Everybody has heard of and knows something about the atomic hypothesis, yet there are few who have been able to follow the more recent researches and speculations of the foremost inquirers in this difficult department, because they have been communicated to the world in a manner in which they can only be understood by mathematicians of the highest order. Such masterminds are necessary, and it was perhaps fortunate for mankind that they have hitherto confined themselves more or less exclusively to original research, and not frittered away their time by writing popular works; but it is the duty of humbler intellects to interpret their revelations, and give them the widest possible dissemination.

There is, in my opinion, no subject, outside of mathematics, however intricate or abstruse in some of its aspects, which can not be explained in the ordinary language of the people. What can be clearly imagined can also be clearly expressed; or we might as well carry science and philosophy back to the time of Duns Scotus, when it was considered the greatest triumph of learning to sophisticate so profoundly, and hedge around with arguments an obvious absurdity that no ordinary intellect could refute it.

I would also like to observe that in the manner in which I shall here endeavor to place this subject before my readers I have been largely influenced by the perusal of a recent work on molecular dynamics by Lasswitz, a German physicist and philosopher, little known as yet in this country, a profound thinker. To this work, which can not fail to make a great impression on all cultured minds, I am indebted for many of the similes which I intend to make use of. Some of these similes may appear fanciful or extravagant, but a little reflection will show their fitness and value in the interpretation of some of the more difficult problems with which we are here confronted.

Let us imagine ourselves, on a cold and clear winter night, suddenly transferred from this greatest and noisiest of American cities, hundreds of miles away, into the stillness of the country, or into the depth of some solitary forest.

Nothing around us seems to stir; we are far from the roar of cities; above us the silence of the stars, beneath us a soft carpet of snow; not a sound to be heard, not a breath of wind stirring the branches.

And yet we know that all this is an illusion! Those bright points of light on the dark firmament are solar systems, whirling through space two hundred times faster than a cannon-ball, and under our feet the delicate snow-crystals are groups of atoms, which tremble with billions of vibrations every second.

The outer forms of the little snow-stars appear to us fixed and rigid like those of the bright constellations above. But from their surfaces a pale light enters our eyes, acts on the retina, and excites the optic nerve—an infallible proof that there is something active even in these—and we know of only one kind of activity in this universe, namely, that of motion.

The particles of which the snow-crystals are composed are not closely joined or cemented to each other like the stones in a wall. They are perpetually acting and reacting on the bodies which surround them, through the medium of an exceedingly fine substance which we term world-ether. It is the bearer of the movements, the effects or modifications of which we know as light, heat, electricity, chemical affinity, etc.; it also keeps the particles of the snow-crystals separate, maintains them in a state of mutual equilibrium, and regulates their vibrations. These vibrations we term the "mechanical cause of heat," because we are aware that every increase of temperature is represented by an increase in the rapidity of the vibrations.

These minute particles, of which, as we know, all bodies consist, are called molecules. In solids, as, for instance, the snow-crystals, they are arranged in a certain fixed order, and their vibration is limited to a given space. Now, let the sun shine on the snow.

The sun is a vast center of activity. From every point of its surface an enormous number of impulses are continually acting on the atoms of the surrounding ether, which are sent through space in every direction, with lightning-like rapidity. The number of these impulses has been estimated at from four to eight hundred billions per second. They give rise to a wave-like motion which traverses about two hundred thousand miles of space per second, and requires eight minutes to reach our earth.

If these ether-waves happen to come into contact with our optic nerve, we experience the sensation of light; if they impinge upon our skin, we feel warmth; if they strike the snow, they set its molecules, as well as the ether between them, into a livelier state of motion. The vibration of the molecules increases in violence, and the result is an increase in temperature in the snow. The particles have to move further away from each other, as their vibrations require more space—we say the heat expands the bodies. At length the vibrations become so energetic that the fixed order in which the particles are arranged can no longer be maintained. They begin to collide and interfere with each other; the whole artificial edifice of the crystal collapses. The molecules can not regain their equilibrium—the snow has changed into water.

In liquids the molecules move about in all directions, yet none of them can voluntarily separate itself from the main body. Just as in a vessel, completely filled with live eels, each individual fish may wriggle and move about among the others, yet it can not detach itself or swim away from them. The liquid particles are not yet sufficiently potent or energetic to overcome the pressure exerted upon them by their surroundings. Above the water, even in the open vessel, they have to encounter the pressure of the atmosphere, the molecules of which keep up a constant and vigorous bombardment against the liquid particles, forcing them down. Still, this can not prevent that here and there a favorably situated water-molecule pushes itself between the air-molecules; the water evaporates. Now, if the temperature is heightened—that is, if the vibrations of the water-molecules increase to such an extent that they can hold their own against the pressure of the air—then a condition of things is brought about familiar to us under the name of boiling. The water-particles shoot about very rapidly; they are no longer crowded together, they force their way through the air-molecules and disperse—the water evaporates; we have no longer liquid but gaseous water.

In gases—as, for instance, the air, carbonic acid, etc.—the molecules are in a state of vibration so violent that they fly about with marvelous rapidity in all directions.

Now, we are in possession of information—of pretty accurate information—respecting these molecule-movements. The researches of men like the late Prof. Kingdon Clifford, Prof. Helmholtz, and, above all, Sir William Thomson—one of the ablest physicists and beyond comparison the greatest living mathematician as well as one of the subtlest thinkers the world has ever produced—the researches of men like these have thrown quite a flood of light on this important and highly interesting subject. Nor is our information merely confined to molecular movements and vibrations; the dimensions of the molecules themselves have been approximately ascertained, because, from known facts of pressure, friction, and heat-conducting capacity, very reliable conclusions can and have been drawn.

The air which surrounds us is a chaos of innumerable minute solid bodies, flying rapidly about in all directions. Our skin is perpetually bombarded by them, and it is this bombardment which causes us to experience atmospheric resistance or pressure. These air-molecules, if closely packed (without any intervening space), would only fill about 13000 of the space taken up by the air as it is. They rush about in this void with the quickness of rifle-bullets. Every point of our skin is struck by at least five thousand millions of these little bullets every second. Their number is so great that every cubic inch of air contains no less than twenty-one trillions of them, and the same is true of all gases. They are so small that they are utterly beyond our powers of perception.

The smallest object which the best and most powerful combination of lenses, as now produced, would still enable us to recognize, requires a diameter of at least 14000000 of an inch, but of oxygen-molecules three hundred could be placed side by side before they would cover that minute distance. Still smaller are the molecules of hydrogen.

Now, in order to get a clear idea of this air which we inhale, of this hail-storm of little worlds which we perpetually encounter without apparent discomfort, let us resort to a little arithmetic and imagination—not the imagination of the poet and romancer, which delights in pictures of the fanciful and ideal, without taking much account of facts, but the healthy imagination of the scientist, which moves among the sternest of all realities, and which, if rightly exercised, becomes a potent factor in the elucidation of truth.

In this glass of water I observe a little air-bubble. It has a diameter of perhaps one thirtieth of an inch. Let us magnify this tiny bubble ten million times; let us imagine it ten million times larger than it is now, but first let us retire to a safe distance; for, the moment we touch it with our magic wand, it becomes a globe eight miles in diameter. In this globe fifty thousand billion little bullets, of the size of No. 6 shot, are flying about in all directions with the quickness of rifle-balls. Whenever one of these molecules, these shot-grains, comes in contact with another (and this happens about eighty million times every second), it is deflected from its course and takes another direction, but without the slightest loss of its original speed.

It may be asked. How can we manage to exist amid such a torrent of projectiles? we ought to be instantly annihilated. But we have forgotten to apply the same magnification-scale to our own persons. Let us do so, and we become giants seven thousand geographical miles in height. One of our feet would more than cover the distance from Chicago to New York, and with the other we could conveniently step across the Atlantic to Europe. Let the whole atmosphere be magnified in the same proportion, and it will be understood why the hail of little bullets perpetually bombarding our skin would not inconvenience us, for that skin would have a thickness of from six to eight miles. The bombardment would produce no other sensation than we now experience when a gentle breath of air fans our cheeks.

The picture which I have here presented is by no means the product of a mere fantastic flight of imagination, but a conclusion strictly warranted by mathematical facts, and necessary for the interpretation of the physical phenomena of nature.

But chemistry has to go yet one step further, in order to explain and render intelligible the phenomena of combination and affinity. We are driven to the conclusion that molecules are not the ultimate particles of matter, but are built up of still smaller bodies, the atoms. Thus, for instance, in a molecule of water we have two atoms of hydrogen united to one of oxygen, and all chemical processes have their source in the fact that the atoms of two or more molecules of different substances detach themselves and reunite again in a different fashion.

Now, in order to obtain a better idea of the manner in which the atoms are grouped in a molecule, we must look upon the latter as a duster, the various parts of which are combined by a well-regulated movement into a harmonious system. "We may well resort, for comparison, to a process within our observation, though on a far grander scale, which is admirably adapted for illustration. Let us look to our planetary system.

The planets, with the sun, represent a stable system, just as the atoms of a molecule represent such a one. In the case of our solar system, the mass of the planets, compared with that of the central body, is, of course, very insignificant. A far closer resemblance to our molecules is therefore presented by those systems of the stellar world in which two or more large bodies, of nearly the same size, revolve around their common center of gravity.

This parallel between atoms and planets, molecules and solar systems, opens before us a new and startling perspective. It affords us a glance into that unfathomable abyss which hides the mysteries of time and space, and holds in its dark recesses the very secrets of existence.

Astronomical science has shown that our sun, with the majority of the fixed stars visible to us, constitutes a great star-cluster, the diameter of which must be estimated by hundreds, if not thousands, of billions of miles. Of such star-clusters there exist a great many, which, in their turn again, form a still grander system, to which we also belong, and the boundaries of which are indicated by the outermost limits of the milky way.

How many of such galaxies may be hidden in the vastnesses beyond, in the bosom of infinite space, we will never know, for the light can only reach us from limited distances. Whatever may be beyond that very farthest nebula, the pale light of which has taken fifteen thousand years to reach us, is concealed from us forever.

But, as here in an outward and ever-enlarging scale, so in the molecules and atoms downward, and ever diminishing in size, we find system after system inclosed one in the other, like the ivory balls in a Chinese puzzle, downward, ever downward, and there is no end! We shall never be able to exhaust the possibilities of minuteness. The atoms of elements may consist of ether-atoms; indeed, the very elements themselves may not be elements in the true sense at all, but compound bodies, as has, indeed, been very long suspected.

Now, let us once more take our magic wand; let us imagine one of these tiny atoms enlarged to the size of this globe, of this earth, on which we live. A magnification of one trillion diameters would more than suffice. It would now, with its companion-atoms, represent a planetary system, and the molecules in a gas would stand in about the same relationship to each other as the fixed' stars over us, which pursue their unknown courses; the little air-bubble in the glass of water becomes a star-cluster like the one in which our sun is situated. The circle of little bubbles around the margin of this glass would represent such a gathering of star-clusters as we now see before us in the milky way.

The galaxy in a glass of water! On what does the glass rest in which our starry firmament has gathered? Who will take it to his lips? We know not; we can not see beyond our tiny bubble, and the mere fact of being able to understand that we never can hope to look beyond it presupposes a great deal of understanding.

It will be worth our while to have a look around on our enlarged atom. We live on this planet of ours, but what entitles us to draw a line or fix a limit as to the possible or impossible in this endless, this infinite series of worlds with which we are here confronted? If we could descend on to one of these atoms, our bodies diminished in proportion, might we not, would we not, find there another earth grouped with its companion-atoms into a stellar system of perhaps wondrous regularity? That world in which a conscious being exists is determined by the kind of this consciousness, and by the character of the impressions which it is capable of receiving. We can not well think of perceptions other than our own, because we can not go beyond the limit of our own selves, but we can well imagine a world in which sensations like ours may succeed each other in far greater rapidity.

We can imagine a creature which in one second, during which we only receive at the utmost ten different impressions, is organized to receive thousands, millions, or billions. That means that in one thousandth, one millionth, or one billionth of the time we live, it experiences the same number of things as we do from the cradle to the grave. Its measure of time, compared with ours, would be infinitely smaller.

Such a being could live on an atom just as conveniently as we live on this planet of ours. If, for instance, the quickness of its sensations were to ours as one thousand trillions is to one, it would experience in the time of one light-vibration—that is, in one five hundred billionth of a second—as much as we in eight months. The atom on which it lived would be its world; the molecule to which the latter belonged, its solar system; and by the revolution of atoms it could count its days and years. Above him, our atom-citizen would see other similar and far-distant worlds; for, the molecules, perhaps all belonging to one tiny air-bubble, would form the star-cluster of his firmament.

A magnification of ten thousand trillion diameters would enlarge the little air-bubble to the dimensions of our entire stellar system, the star-cluster of which the limits are the outermost regions of the milky way. But, great as the host of our stars may appear to us, the firmament of our atom-inhabitant would be still more densely crowded; for while we, with the aid of our best telescopes, can not see more than about twenty million stars, the little air-bubble would harbor at least fifty thousand billions.

Now, you might object that, to an atom-inhabitant, the molecules of a gas could not possibly appear as the fixed stars do to us, inasmuch as these molecules experience, on an average, about eighty million collisions in every second. However, it must not be forgotten that we have reduced the time of life and observation of our atom-inhabitant to one thousand trillionth that of our own. During this brief moment the relative positions of the visible molecules—to him far-distant suns—will appear just as unaltered, and their courses or orbits to the atom-astronomers just as linear, as those of our fixed stars appear to us.

What is the short space of time, the trifling moment, that we know of the life-history of the earth, compared with the eternities which must elapse before two fixed stars approach sufficiently close to render a collision inevitable? Our records of human history read back only a few thousand years, and of the age of our planet we only know that it must be measured by thousands of centuries. Of the courses of the fixed stars we know absolutely nothing; we only infer from certain data that their average velocity is about a hundred times greater than that of our molecules.

Thus the atom-inhabitants are about as wise as we are. The life of the entire human race, so far as our historical records are concerned, would, if condensed to one thousand trillionth, occupy about the one thousand millionth part of a second—less than one twentieth of the time which elapses, on an average, before the collision of two gas-molecules—time enough for thousands and tens of thousands of generations of living beings to rise, flourish, and decay, before a perceptible alteration of their starry firmament can be recorded.

It remains to fancy to picture further how those atom-inhabitants imagine their world as the only world civilized and blessed by divine ordaining, for they know as little of other worlds as we do. Millions of their years may pass—by thousands the rise and fall of their nations, the dynasties of their rulers, the triumphs of their philosophers and poets may be recorded—before the water-glass with the little air-bubble, in which their planet is merely the tiniest atom, is seized by human hands, and billions of worlds are drawn in by human lips.

What an endless vista of life is here presented to us! Not enough that the vast space which surrounds us is peopled by innumerable worlds like ours, but within the latter new worlds are presented in the atoms, which in their turn again may harbor others still smaller, and so on in infinite succession.

And now the same step upward! Let us regard our earth as an atom, our solar system as a molecule. Of what larger body may it, with all the galaxies and star-clusters, constitute a particle? What a giant-world may that be, what creatures may inhabit it? Our universe, encircled by its galaxy of myriad suns, is it but a stray bubble floating on some mighty ocean of that greater world? This stellar system of ours, does it perhaps, in that giant-world, represent a molecule in some complicated organic structure—a nerve-cell in a giant organism, perhaps a brain-particle in the head of a Titan, whose feet rest on ground in the abysmal distances of space?

That Titan would have a height, if his body were proportional to ours, equal to a billion Sirius-distances! What thoughts, what sensations may move him, when, in his brain-cells, our suns clash in stupendous conflict and meet their doom in universal conflagration! And those Titans, whose bodies, whose terra firma is composed of veritable oceans of star-clusters, what a starry world may they behold above them! On the atoms now vibrating in our own brains, in the blood coursing through our veins, the destinies of nations may be fulfilled, destinies on the planets, which again are but the atoms of a higher world, destinies on the giant-worlds, and none of the beings is aware of the existence of the others; each has the solid ground beneath him, and above him the silence of the stars.

Therefore, if this thought should make us feel uneasy—the thought that this cherished world of ours is but an atom in a giant-world—let us take consolation in this: the giants are in no way better situated than we are in reference to the dwarfs which inhabit the world of atoms. Stars above them, the ground beneath them, that is their world as it is ours. That we just happen to exist on the earth is a matter of comparative indifference. No matter where we might be, our astronomers would always investigate the starry firmament, our chemists and physicists would divide bodies into molecules and atoms. Everywhere the suns as the atoms would pursue their courses in obedience to the same laws, everywhere two sides in the triangle would be greater than the third, and everywhere twice two seconds would make four. That is the law for the giants and the dwarfs, the law beyond which we shall never be able to rise.