Page:Modern Views on Matter.djvu/26

 18 diminution or cessation. There is every reason to believe that a minute scrap of radium, scarcely perceptible to the eye, may go on emitting these energetic projectiles for hundreds of years.

11. At first sight the fact that it is merely atoms of matter which are being flung off by most radio-active substances, and that ethereal and other effects are subsidiary to this emission of substance, seems to lessen the interest attaching to the phenomenon, reducing it to something of merely chemical importance, and suggesting a resemblance to scent or other volatilization from solid bodies. But Professor Rutherford, with great skill, succeeded in determining approximately the atomic weight of the utterly imperceptible amount of substance thrown off as well as its speed and found that it was not by any means the radio-active substance itself which was evaporating, but something quite different.

Plainly if an elementary form of matter is found to be throwing off another substance, it becomes imperative to inquire what that substance is, and what it is that is left behind. Now the atomic weight of radium, or of thorium or uranium, or of any known strongly radio-active substance, is very high, in each case over 200 times the atomic weight of hydrogen, whereas the atomic weight of the substance flung off appears to be more nearly of the order 1 or 2; in other words, the substance thrown off is more likely to be either hydrogen or helium than it is likely to be radium. (It is just possible, as Rutherford and Soddy suggest, that the inert chemical elements are bye-products of radio-activity.)