RADIO-ACTIVITY 199 



gram of radium could furnish If entirely dis- 

 integrated seems to be enough to raise the 

 temperature of about 1.5 x 10^^ grams, or about 

 15,000 tons of water, through one degree centi- 

 grade. We may say that, in mechanical units, 

 the energy available for radiation in one ounce 

 of radium is sufficient to raise a weight of some- 

 thing like five thousand tons one mile high. 



It will now be clear that, on the theory which 

 has been put forward, we are, while investigating 

 a radio-active body, in reality watching the process 

 of the transmutation of matter. Radio-active 

 substances, themselves unstable, may have been 

 formed by the disintegration of parent atoms, 

 which are unknown to us, and, indeed, may now 

 be non-existent on our globe. Radio-activity 

 denoting an unstable state, it is probable that 

 the total amount of it in the world is constantly 

 diminishing, as the atoms of the active elements 

 pass gradually into inactive forms. Perhaps in 

 former ages nearly all matter was intensely radio- 

 active ; and mankind has discovered these phe- 

 nomena only in the last cosmical moments of a 

 few thousand or million years before they cease 

 for ever to manifest their existence in the striking 

 manner which has made radium so remarkable. 



When we trace in this way the creation and 

 evolution of new elements, it is impossible to resist 

 wondering whether the process of change, so far 

 observed to an appreciable extent only in a 

 few radio-active bodies, may not in reality be a 

 general property of matter, though in other cases 

 possessed in such an infinitesimal degree that it 

 almost transcends the delicate means of detection 



