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A History of Science, Volume 5(of 5) by Williams

The corpuscles taking the place of the molecules


as the smallest mass able to

have an independent existence. Professor Thompson gave the name corpuscle to these units of negative electricity; they are now more generally termed electrons. "These corpuscles," he says, "are the same however the electrification may have risen or wherever they may be found. Negative electricity in a gas at a low pressure has thus a structure analogous to that of a gas, the corpuscles taking the place of the molecules. The 'negative electric fluid,' to use the old notation, resembles the gaseous fluid with a corpuscular instead of a molecular structure.'" Professor Thompson does not hesitate to declare that we now "know more about 'electric fluid' than we know about such fluids as air or water."*3* The results of his studies lead him, he declares, "to a view of electrification which has a striking resemblance to that of Franklin's _One Fluid Theory of Electricity_. Instead of taking, as Franklin did, the electric fluid to be positive electricity," he says, "we take it to be negative. The 'electric fluid' of Franklin corresponds to an assemblage of corpuscles, negative electrification being a collection of these corpuscles. The transference of electrification from one place to another is effected by the motion of corpuscles from the place where there is a gain of positive electrification to the place where there is a gain of negative. A positively electrified body is one that has lost some of its corpuscles."*4* According to this view, then, electricity is not a form of energy
but a form of matter; or, to be more precise, the electrical corpuscle is the fundamental structure out of which the atom of matter is built. This is a quite different view from that scarcely less recent one which regards electricity as the manifestation of ether strain, but it must be admitted that the corpuscular theory is supported by a marvellous array of experimental evidence, though it can perhaps hardly be claimed that this brings the theory to the plane of demonstration. But all roads of physical science of late years have seemed to lead towards the electron, as will be made further manifest when we consider the phenomena of radio-activity, to which we now turn.

RADIO-ACTIVITY

In 1896, something like a year after the discovery of the X-ray, Niewenglowski reported to the French Academy of Sciences that the well-known chemical compound calcium sulphide, when exposed to sunlight, gave off rays that penetrated black paper. He had made his examinations of this substance, since, like several others, it was known to exhibit strong fluorescent or phosphorescent effects when exposed to the cathode rays, which are known to be closely connected with the X-rays. This discovery was followed very shortly by confirmatory experiments made by Becquerel, Troost, and Arnold, and these were followed in turn by the discovery of Le Bon, made almost simultaneously, that certain bodies when acted upon by sunlight give out radiations which act upon a photographic plate. These manifestations, however, are not the effect of radio-activity, but are probably the effects of short ultra-violet light waves, and are not produced spontaneously by the substances. The radiations, or emanations, of the radio-active substances, on the other hand, are given out spontaneously, pass through substances opaque to ordinary light, such as metal plates, act upon photographic plates, and discharge electrified bodies. The substances uranium, thorium, polonium, radium, and their compounds are radioactive, radium being by far the most active.


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