We saw at the very beginning of this little book that, from time immemorial, something corresponding to Atoms were regarded as the ultimate “building stones” of the universe--tiny particles, incapable of diversion, beyond which it was impossible to go. Beginning with Epicurus and Democritus, this idea took scientific form; it was held by many philosophers throughout the ages; it formed the basis of Dalton’s atomic theory, and was assumed by the Periodic Law. It was not until the last years of the preceding century that this idea was called into question. The discovery of _radium_, by the Curies, caused a sensation in the scientific world. How account for the phenomena observed? Radium seemed to give off energy continuously, without losing any; heat was constantly being radiated without lessening the original amount. Had the secret of perpetual motion been discovered? What was happening? The discovery of other radio-active elements only tended to increase the problem, instead of solving it. Here was some new property of matter, hitherto unsuspected, going on before the eyes of chemists, which they could not understand or explain. INTRA-ATOMIC ENERGY Professor E. Rutherford, of M’Gill University, Canada, was among the first to propose a new and startling theory. He said: Suppose that the atoms are _not_ indivisible? Suppose that they are capable of being split-up into something still smaller and finer? If the atoms themselves are being disintegrated, immense quantities of energy would probably be available--“intra-atomic energy”--which would account for the results obtained. It is true that we should no longer have our stable atoms; they would vanish and be represented by something else. And that “something” would no longer be matter, in the sense that we now understand it; but we could account for the observed facts (radio-activity, etc.), and we can then endeavor to discover what atoms are resolved into later on. This theory was soon proved to be true; atoms were shown to be divisible, and capable of being split-up into something still smaller, which were no longer “matter” in the old sense. Matter, in short, had technically disappeared, and had been resolved into its component parts. This being so, the question at once arose: Of what is matter (the atom) composed? THE THEORY OF MATTER Without going into great detail, or attempting to trace the history of the various discoveries which led up to it, it may now be stated definitely that matter is built-up of _electricity_. For the proof of this, the scientific world has to thank Sir J. J. Thomson, who first popularized this view in his book “Electricity and Matter.” He was closely seconded by Sir Oliver Lodge, Sir William Crookes, and many other eminent scientists. On this view, matter totally disappears, as such; it becomes super-sensible; it is resolved into energy. Electricity and the ether somehow are responsible for matter, but just _how_ was not at the time understood.