functions, viz. to record a larger or smaller number of isolated or seemingly isolated facts, and to give us some clear idea of a connection between these facts so that we may be able to deduce them one from another and predict new facts that may be discovered by means of new experiments suggested by the theory. Secondly, we must consider that a theory, like a tree, is to be judged by its fruits, and that an unproductive or worn out theory, like an unfruitful tree, must be cast into the fire. It is important that we do not forget this, for the hypothesis that is the subject of this article is as yet incomplete. Its fruits have still to be gathered and tested. There is much which suggests that in due course the electric theory of matter may prove as fruitful as the atomic theory of the nineteenth century, but the electric theory to-day, like the atomic theory a century ago, is still imperfect, still upon its trial. If I may compare it to a tool, we may say that at present we have not the finished tool, but only a rough casting from which, perhaps, a finished tool may be constructed before long.

I need hardly say that it is important my readers should have a clear idea what it is the electric theory of matter has to explain. Perhaps we shall best discover how we stand on this point if we ask ourselves the question, What is matter? What are the isolated facts about matter which this theory must co-ordinate? Now, this question is very difficult to answer. Most of us know a good deal about the surface differences which distinguish the myriad forms in which matter presents itself to us, but our real knowledge of its nature and constitution is slight indeed. According to J. S. Mill, matter is the permanent possibility of sensations.' According to W. K. Clifford it is a mental picture in which mindstuff is the thing represented,' while 'mind-stuff is constituted by feelings which can exist by themselves, without forming parts of a consciousness, but are also woven into the complex form of human minds.' For our present purpose, however, speculations like these retain only an historic importance. For us, as the late Professor P. G. Tait has expressed it, the universe, including matter, has an objective existence, and we become aware of it by the aid of our senses, and, since the evidence of the senses often misleads, we endeavour to sift the mixture of truth from error gained through the use of our senses by the exercise of the reason, for example, by forming theories such as the atomic theory of Dalton and the electric theory of the new physics.

According to the electric theory, matter in all its forms consists, as I have said, of systems of electric charges. This idea is the outcome of the work of the atomists, Dalton and his colleagues, on the one hand, and of the work of Faraday and his great successors on the other. Broadly speaking, we may say that Dalton reinvented atoms for the use of the chemists, that the physicists, with Professor J. J. Thomson at their head, discovered the existence of particles, called electrons, even smaller than atoms, and that authors of the electric theory hope to establish the nature of the electron, and to discover the relation of the electron to the atom.

It is not necessary to dwell for long on the atomic molecular theory, for this has already been fully discussed in the CORNHILL.' It will be sufficient if we remember that according to chemists matter exists in the form of a limited number of elements, about eighty of these elements being known to us, and that each of these elements occurs in the form of characteristic minute unbreakable particles called atoms. I suppose that in modern times few investigators have really believed of any given atom that it would exist for ever, or that it had existed in the past from all eternity. But undoubtedly some of the greatest masters of the modern school, e.g. Clerk Maxwell, have held there is reason to believe that in the atoms of the chemists' we have something which has existed either from eternity, or at least from times anterior to the existing order of nature'; or, to put the point more explicitly, if I may quote Clerk Maxwell' once more, that the creation of an atom is an operation of a kind which is not, so far as we are aware, going on on earth or in the sun or in the stars, either now or since these bodies began to be formed,' and must be referred to the epoch of the establishment of the existing order of nature.

The facts before Clerk Maxwell when he wrote the above words gave him no reason for suspecting that possibly chemical atoms might now and then undergo disintegration under our noses. But to-day, though we are as incompetent as ever to create an atom out of nothing, we are no longer quite convinced that atoms are the smallest particles of matter. This does not mean that the molecular atomic theory is used up and ready for the scrap-heap, for the idea of the atom is as necessary and as useful But atoms no longer seem to us, as to Newton, to be

as ever.

1 See The New Physics and Chemistry, 'On Weighing Atoms.'
2 See 'Atom,' by Clerk Maxwell, Encl. Brit. 9th ed.

solid, massy, hard, impenetrable, indivisible portions of matter. On the contrary, it has become conceivable that they may consist of constellations of much smaller particles; that they may be built up, that is, of parts and possess in each case a definite structure which sooner or later we may hope to understand.

Although, as I have said, we need not dwell for long on the properties of matter, there are two or three points which we must keep in our minds. First, we must remember that every particle of matter great and small exhibits what is known as 'attraction of gravitation'; secondly, that every particle exhibits, also, a kind of passivity or dogged perseverance, called inertia, in virtue of which every body perseveres in its state of rest or of uniform motion in a straight line unless it is compelled by some force to change that state.' This, as you will see, implies that if at any time a particle of matter of sensible mass should cease to be subject to attraction of gravitation, or should lose its inertia, we should have to regard it as destroyed.

The idea that matter in general may be electrical in its origin recommends itself to many minds all the more because it seems to afford us a stepping stone from which we may proceed towards the attainment of a clear idea of a simple material universe composed of a single primitive matter analogous to that which Prout imagined to be the basis of the chemical elements. It is founded upon that view of electricity which regards the latter as possessing an atomic constitution, and regards a certain quantity of electricity as an indivisible unit, as a sort of atom of electricity, a quantity which can only be increased by adding other units to it, like adding bricks to a wall, but which cannot be divided or diminished by any means yet at our disposal.

I suppose every one has seen the well-known and beautiful luminous glow of a vacuum tube. This glow is produced by connecting the poles of an electrical machine to two wires melted into the two ends of a glass tube, and exhausting the tube moderately by means of an air pump. If a vacuum tube in the state in which it gives this glow be further exhausted, its luminosity gradually disappears, breaking up into discs which grow fewer and fewer as the exhaustion proceeds, until at last, if the exhaustion is pushed far enough, no light is seen except a glowing phosphorescence on the surface of the glass, like that which you see when watching experiments with Röntgen ray tubes. It was inside vacuum tubes when highly exhausted that Professor J. J. Thomson recognised,

in 1897, particles far smaller than hydrogen atoms and charged with negative electricity.

If you obtain a glass tube such as I have described, provided at its two ends with two platinum wires sealed into the glass so that the joints are perfectly air-tight, exhaust it by means of an airpump until only about one part in a million of the air originally present in the tube remains there, connect the wires to an electrical machine, and then make suitable experiments, you will discover that though the tube does not become luminous like an ordinary vacuum tube, yet it seems to contain something which possesses some very remarkable properties. For example, if before exhausting the tube you have placed inside it, in front of the cathode and at a convenient distance, a piece of platinum foil, a diamond, or a ruby, and then start the machine, the platinum will soon get hot, as a piece of metal does when you hammer it-if the exhaustion has not been carried too far it may become red hot-whilst the diamond or ruby will become phosphorescent or self-luminous, giving out light rays more or less as a flint does when struck upon steel, except that in the former case the luminosity is not intermittent like a spark from flint and steel, but persists as long as the electric machine is maintained in action. Even if you put no solid object in the tube, somewhat similar phenomena present themselves; for in this case the glass of the tube over a considerable area opposite the cathode glows brightly when the electric machine is in action, and soon becomes hot, as if it were being bombarded violently by something thrown off by the cathode, these effects being accompanied, as I should explain, by the production of Röntgen rays, and occasionally, if one is not careful, by the melting of the glass of the tube.

I think every one will agree that the above phenomena decidedly suggest, as they did to Sir William Crookes when he first observed them, the idea that though the tube is so nearly empty, since only a very minute fraction of the original air remains inside it, streams of something are being driven from the cathode through the tube; that the cathode under the influence of the electric machine creates, in fact, a sort of wind inside the tube-a wind more or less like other winds, but probably exceeding other winds greatly in its velocity, since no wind we are acquainted with outside a vacuum tube is sufficiently violent to melt glass or to raise particles of metal to a red heat.

The idea that streams of invisible particles are thrown off from

1

the cathode of the Crookes vacuum tube has been confirmed by other experiments. Thus if we vary the construction of a vacuum tube by placing the anode not opposite the cathode, as described above, but in other positions, we discover that though both a cathode and an anode are required it is not necessary to place the anode at that part of the tube on which we wish the supposed bombardment to fall; for, place the anode where we may, we find in every case that the radiation flies from the cathode in straight lines, like bullets from a gun, refusing to turn corners except under the influence of a magnet. It may be arrested by some obstacle such as a stone or a small windmill, in which case it will work the windmill as an aerial wind might do. On the other hand, when obstacles are placed in the path of the radiations shadows are formed as if the radiation were unable to pass through the obstacle. The power of obstacles to arrest the rays probably is not perfect, for it is found that cathode rays can, to some extent, escape from a vacuum tube if they fall upon a window made of a very thin sheet of a metal such as aluminium. But though the rays insist on moving in straight lines and refuse to turn corners, if a small beam of cathode rays be thrown on a sheet of card coated with some phosphorescent paint, the luminous spot produced where the beam falls on the paint can readily be moved from one point to another by bringing a powerful magnet to bear upon the beam on its road to the screen. This seems to show that cathode rays can be waved about by the magnet. Remember what you see when you watch the rays of a searchlight cast from a ship which is feeling its way on an unknown coast, and recall how they reveal themselves chiefly by the illumination they produce when they fall on an adjacent object, on a ship, on the shore, or on the sea, and you will have some idea of the effects produced by a magnet on a beam of cathode rays inside a Crookes tube. The little spot of light will play about upon the screen, now here, now there, as you move the magnet, making it plain that the invisible cathode beam which produces the light is moving about in the tube much as we see the rays of a searchlight beam move in the sky at night-time. Now, this power of the magnet upon cathode rays is not only useful because it gives us a means of controlling the movements of the cathode rays, but also because it gives us a very strong hint about the nature of the rays themselves.

It must be remembered that the two wires fused into the vacuum tube are known as the anode and cathode respectively.