Page:Popular Science Monthly Volume 63.djvu/297

Rh The final definite establishment of the fact that these flying particles are not atoms of matter, but are bits chipped off the atoms, fractions of an atom as it were, the same identical kind of bits being chipped off every kind of chemical atom, their mass always about one thousandth of that of a hydrogen atom, and moving under favorable circumstances with something not much less than the speed of light, is due to the researches of Professor J. J. Thomson and his coadjutors in the Cavendish Laboratory, Cambridge, and represents a, long series of measurements devised and executed with consummate skill.

I have no time to go into detail concerning these important and elaborate and most interesting investigations. Suffice it to say that portions of them are due to your own Wykeham professor of physics. Professor Townsend, working in conjunction and collaboration with others, under the leadership of Professor J. J. Thomson; and that this whole series of Cavendish Laboratory researches may be said to constitute the high-water mark of the world's experimental physics during the beginning of this century.

5. I must not dwell upon the properties and powers of electrons, nor upon the experimental means by which these measurements were made, for it is far too large a subject. I must exhibit a few diagrams, and briefly summarize a few main facts.

Electrons have been shown to be shot off from any negatively charged body, especially from negatively electrified metals, when exposed to ultra-violet light.

When shot into a mass of air they ionize that air for a time, and render it electrolytically conducting; also of course they can discharge positively electrified bodies themselves, and can thus be most readily detected in small numbers.

Electrons in orbital motion have been shown to constitute the mechanism by which atoms are able to radiate light; and a great mass of semi-astronomical facts concerning these orbits and their perturbations have been obtained by immersing the source of light in a strong magnetic field, and observing the minute but very definite changes of spectra thereby produced: a branch of science with which the names of H. A. Lorentz, of Leyden, and Zeeman, of Amsterdam, will be inseparably associated.

In all these and other ways the electron has become a familiar object. It constitutes the ionic charge of matter. Multiples of it, but no fractions, are possible. Its mass, its charge and its speed have been frequently measured by different processes, and always with consistent results. It is the most definite and fundamental and simple unit which we know of in nature.

It has thus displaced the so-called atom of matter from its fundamental place of indivisibility. The atom of matter has been shown