to the bombardment of the α particles expelled from these substances. It has already been pointed out (section 136) that it is difficult to imagine any mechanism, either internal or external, whereby such enormous velocity can suddenly be impressed upon the α particles. We are forced to the conclusion that the α particle did not suddenly acquire this energy of motion, but was initially in rapid motion in the atom, and for some reason, was suddenly released with the velocity which it previously possessed in its orbit.
The strongest evidence against the hypothesis of absorption of external energy is that such a theory ignores the fact, that, whenever radio-activity is observed, it is always accompanied by some change which can be detected by the appearance of new products having chemical properties distinct from those of the original substances. This leads to some form of "chemical" theory, and other results show that the change is atomic and not molecular.
256. Theory of radio-active change. The processes occurring
in the radio-elements are of a character quite distinct from any
previously observed in chemistry. Although it has been shown
that the radio-activity is due to the spontaneous and continuous
production of new types of active matter, the laws which control
this production are different from the laws of ordinary chemical
reactions. It has not been found possible in any way to alter
either the rate at which the matter is produced or its rate of
change when produced. Temperature, which is such an important
factor in altering the rate of chemical reactions, is, in these cases,
almost entirely without influence. In addition, no ordinary
chemical change is known which is accompanied by the expulsion
of charged atoms with great velocity. It has been suggested
by Armstrong and Lowry[1] that radio-activity may be an
exaggerated form of fluorescence or phosphorescence with a very
slow rate of decay. But no form of phosphorescence has yet been
shown to be accompanied by radiations of the character of those
emitted by the radio-elements. Whatever hypothesis is put
forward to explain radio-activity must account not only for the
production of a series of active products, which differ in chemical
- ↑ Armstrong and Lowry, Proc. Roy. Soc. 1903. Chem. News, 88, p. 89, 1903.
