energy from the enclosures or from surrounding bodies; or, if not made up, it can produce the ordinary well-known effects of 'cold.' But to the motion of the internal parts of an atom the ideas of heat and temperature do not apply. The atom, if it lose energy, must lose what is to it an essential ingredient; and hence this inevitable radiating power of the constituents of an atom seemed to constitute a difficulty, for it suggested that an atom of matter was not really a permanent and eternal thing, but that it contained within itself the seeds of its own decay and ultimate dissipation into the separate electrons of which it was composed. The process might indeed be exceedingly slow, the radiation loss might be almost imperceptible, but, in so far as an atom is composed of revolving electrons, it is inevitable that radiation of energy must go on from it, and that this must in the long run have some perceptible degenerative result.
10. That result has quite recently, I believe, been experimentally discovered, and is a part of the phenomenon known as 'radio-activity.'
So now we come to the most remarkable and probably the most interesting step of all.
The phenomenon of spontaneous radio-activity, discovered first by Becquerel in uranium and thorium, and greatly extended by the brilliant chemical researches of M. and Mme. Curie which resulted in the discovery of radium, was at first supposed to consist in the emission of a sort of X-rays or ether pulses; and was subsequently assumed to consist chiefly in the bodily emission of electrons, which were shot off from the
