THE ENERGY OF RADIUM 17 



combustion of the same weight of coal, the source 

 of energy on which the world, in so far as it is 

 modern, subsists. 



Whence arises such a stream still flowing in this 

 world of ancient lineage, from a material extracted 

 from minerals found in rocks, many of them coeval 

 with the beginning of geological time? Tracked to 

 earth, the clue to the great secret, for which a 

 thousand telescopes might have swept the sky for 

 ever and in vain, lay in a scrap of matter, dowered 

 with something of the same inexhaustible radiance 

 that hitherto has been the sole prerogative of the 

 distant stars and sun. 



The solution of these problems followed the proof 

 that the energy of radioactive substances was evolved 

 in new kinds of change, which are distinguished from 

 those studied in chemistry in two ways. In the 

 first place they are more fundamental, and concern 

 a plane in the complexity of matter hitherto not 

 penetrated. It is the unit of matter, indivisible in 

 chemical changes, the atom of the radioactive 

 element, which in radioactive changes subdivides or 

 disintegrates. Secondly, per unit weight of matter 

 changing, energy of the order of a million times 

 greater than in any previously known change is 

 given out. 



Just as chemical changes, the disruption and 

 formation of molecules and the rearrangement of 

 the component atoms out of which they are built 

 such changes as the explosion of dynamite or 

 gunpowder occur with far greater corresponding 

 changes of energy than physical changes, like the 

 change of state in the vaporisation of water or con- 

 densation of steam, so with these new changes, which 

 are concerned with the inner architecture of atoms. 

 All material processes studied hitherto have been con- 

 cerned solely with the external relationships of atoms. 



