After we have reached the point of the utmost divisibility of matter in the atom, we are called upon to go still further and divide the indivisible. The electrons, of which the atom is composed, are one hundred thousand times smaller, and two thousand times lighter than the smallest particle hitherto recognized, namely, the hydrogen atom. A French physicist conceives of the electrons as rushing about in the interior of the atom like swarms of gnats whirling about in the dome of a cathedral. The smallest particle of dust that we can recognize in the air is millions of times larger than the atom, and millions of millions of times larger than the electron. Yet science avers that the manifestations of energy which we call light, radiant heat, magnetism, and electricity, all come from the activities of the electrons. Sir J. J. Thomson conceives of a free electron as dashing about from one atom to another at a speed so great as to change its location forty million times a second. In the electron we have matter dematerialized; the electron is not a material particle. Hence the step to the electric constitution of matter is an easy one. In the last analysis we have pure disembodied energy. "With many of the feelings of an air-man," says Soddy, "who has left behind for the first time the solid ground beneath him," we make this plunge into the demonstrable verities of the newest physics; matter in the old sense—gross matter—fades away. To the three states in which we have always known it, the solid, the liquid, and the gaseous, we must add a fourth, the ethereal—the state of matter which Sir Oliver Lodge thinks borders on, or is identical with, what we call the spiritual, and which affords the key to all the occult phenomena of life and mind.
As we have said, no human eye has ever seen, or will see, an atom; only the mind's eye, or the imagination, sees atoms and molecules, yet the atomic theory of matter rests upon the sure foundation of experimental science. Both the chemist and the physicist are as convinced of the existence of these atoms as they are of the objects we see and touch. The theory "is a necessity to explain the experimental facts of chemical composition." "Through metaphysics first," says Soddy, "then through alchemy and chemistry, through physical and astronomical spectroscopy, lastly through radio-activity, science has slowly groped its way to the atom." The physicists make definite statements about these hypothetical bodies all based upon definite chemical phenomena. Thus Clerk Maxwell assumes that they are spherical, that the spheres are hard and elastic like billiard-balls, that they collide and glance off from one another in the same way, that is, that they collide at their surfaces and not at their centres.
Only two of our senses make us acquainted with matter in a state which may be said to approach the atomic—smell and taste. Odors are material emanations, and represent a division of matter into inconceivably small particles. What are the perfumes we smell but emanations, flying atoms or electrons, radiating in all directions, and continuing for a shorter or longer time without any appreciable diminution in bulk or weight of the substances that give them off? How many millions or trillions of times does the rose divide its heart in the perfume it sheds so freely upon the air? The odor of the musk of certain animals lingers under certain conditions for years. The imagination is baffled in trying to conceive of the number and minuteness of the particles which the fox leaves of itself in the snow where its foot was imprinted—so palpable that the scent of a hound can seize upon them hours after the fox has passed! The all but infinite divisibility of matter is proved by every odor that the breeze brings us from field and wood, and by the delicate flavors that the tongue detects in the food we eat and drink. But these emanations and solutions that affect our senses probably do not represent a chemical division of matter; when we smell an apple or a flower, we probably get a real fragment of the apple, or of the flower, and not one or more of its chemical constituents represented by atoms or electrons. A chemical analysis of odors, if it were possible, would probably show the elements in the same state of combination as the substances from which the odors emanated.
The physicists herd these ultimate particles of matter about; they have a regular circus with them; they make them go through films and screens; they guide them through openings; they count them as their tiny flash is seen on a sensitized plate; they weigh them; they reckon their velocity. The alpha-rays from radio-active substances are swarms of tiny meteors flying at the incredible speed of twelve thousand miles a second, while the meteors of the midnight sky fly at the speed of only forty miles a second. Those alpha particles are helium atoms. They are much larger than beta particles, and have less penetrative power. Sir J. J. Thomson has devised a method by which he has been able to photograph the atoms. The photographic plate upon which their flight is recorded suggests a shower of shooting stars. Oxygen is found to be made up of atoms of several different forms.
III
The "free path" of molecules, both in liquids and in gases, is so minute as to be beyond the reach of the most powerful microscope. This free path in liquids is a zigzag course, owing to the perpetual collisions with other molecules. The molecular behavior of liquids differs from that of gases only in what is called surface tension. Liquids have a skin, a peculiar stress of the surface molecules; gases do not, but tend to dissipate and fill all space. A drop of water remains intact till vaporization sets in; then it too becomes more and more diffused.
When two substances combine chemically, more or less heat is evolved. When the combination is effected slowly, as in an animal's body, heat is slowly evolved. When the combustion is rapid, as in actual fire, heat is rapidly evolved. The same phenomenon may reach the eye as light, and the hand as heat, though different senses get two different impressions of the same thing. So a mechanical disturbance may reach the ear as sound, and be so interpreted, and reach the hand as motion in matter. In combustion, the oxygen combines rapidly with the carbon, giving out heat and light and carbon dioxide, but why it does so admits of no explanation. Herein again is where life differs from fire; we can describe combustion in terms of chemistry, but after we have described life in the same terms something—and this something is the main thing—remains untouched.
The facts of radio-activity alone demonstrate the truth of the atomic theory. The beta rays, or emanations from radium, penetrating one foot of solid iron are very convincing. And this may go on for hundreds of years without any appreciable diminution of size or weight of the radio-active substance. "A gram of such substance," says Sir Oliver Lodge, "might lose a few thousand of atoms a second, and yet we could not detect the loss if we continued to weigh it for a century." The volatile essences of organic bodies which we detect in odors and flavors, are not potent like the radium emanations. We can confine them and control them, but we cannot control the rays of radio-active matter any more than we can confine a spirit. We can separate the three different kinds of rays—the alpha, the beta, and the gamma—by magnetic devices, but we cannot cork them up and isolate them, as we can musk and the attar of roses.
And these emanations are taking place more or less continuously all about us and we know it not. In fact, we are at all times subjected to a molecular bombardment of which we never dream; minute projectiles, indivisible points of matter, are shot out at us in the form of electrons from glowing metals, from lighted candles, and from other noiseless and unsuspected batteries at a speed of tens of thousands of miles a second, and we are none the wiser for it. Indeed, if we could see or feel or be made aware of it, in what a different world we should find ourselves! How many million-or billion-fold our sense of sight and touch would have to be increased to bring this about! We live in a world of collisions, disruptions, and hurtling missiles of which our senses give us not the slightest evidence, and it is well that they do not. There is a tremendous activity in the air we breathe, in the water we drink, in the food we eat, and in the soil we walk upon, which, if magnified till our senses could take it in, would probably drive us mad. It is in this interior world of molecular activity, this world of electric vibrations and oscillations, that the many transformations of energy take place. This is the hiding-place of the lightning, of the electrons which moulded together make the thunderbolt. What an underworld of mystery and power it is! In it slumbers all the might and menace of the storm, the power that rends the earth and shakes the heavens. With the mind's eye one can see the indivisible atoms giving up their electrons, see the invisible hosts, in numbers beyond the power of mathematics to compute, being summoned and marshalled by some mysterious commander and hurled in terrible fiery phalanxes across the battlefield of the storm.
The physicist describes the atom and talks about it as if it were "a tangible body which one could hold in his hand like a baseball." "An atom," Sir Oliver Lodge says, "consists of a globular mass of positive electricity with minute negative electrons embedded in it." He speaks of the spherical form of the atom, and of its outer surface, of its centre, and of its passing through other atoms, and of the electrons that revolve around its centre as planets around a sun. The electron, one hundred thousand times smaller than an atom, yet has surface, and that surface is a dimpled and corrugated sheet—like the cover of a mattress. What a flight of the scientific imagination is that!