The Evolution of the Sciences 



and just criticisms, but chemists, almost without 

 exception, look upon it as the screen on which the 

 more general properties of matter group them- 

 selves; it gives a precise form, too precise and 

 simple, perhaps, to the indisputable interdepend- 

 ence of all the elements. 



Modern chemistry, as we have seen, while 

 admitting the conception of elements, noted 

 among them correlations, which suggested the 

 possibility of transmutations; but the means 

 at its disposal were insufficient to realise this. x 



The discovery of the radio-active bodies sup- 

 plied the necessary lever. These bodies, uranium, 

 thorium, radium, actinium, are a marvellous and 

 to all appearance inexhaustible source of energy. 

 Radium in particular, the best known of all, emits 

 incessantly light, heat and three kinds of radia- 

 tion, which have been designated by the letters, 

 a } ft, y. The a rays, according to Rutherford, are 

 formed by molecules of helium, a gas four times 

 denser than hydrogen, with a positive electric 

 charge, and animated with a moderate speed. 



1 In 1900, Fittica, Professor at the University of Marburg, 

 thought he had succeeded in transforming phosphorus into 

 arsenic. But like all those of his predecessors his attempt ulti- 

 mately failed. 



72 



