248 THE HISTORY OF SCIENCE 



radium and in determining the atomic weight of the 

 new element. There is (according to Soddy) about 

 one part of radium in five million parts of the best 

 pitchblende, but the new element is about one mil- 

 lion times more radioactive than uranium. It was 

 calculated by M. Curie that the energy of one gram 

 of radium would suffice to lift a weight of five hun- 

 dred tons to a height of one mile. After discussing 

 the bearing of the discovery of radioactivity on the 

 threatened exhaustion of the coal supply Soddy 

 writes enthusiastically : " But the recognition of the 

 boundless and inexhaustible energy of Nature (and 

 the intellectual gratification it affords) brightens the 

 whole outlook of the twentieth century." The ele- 

 ment yields spontaneously radium emanation without 

 any apparent diminution of its own mass. In 1899 

 Debierne discovered, also in the highly complex 

 pitchblende, actinium, which has proved considerably 

 less radioactive than radium. During these investi- 

 gations M. and Mme. Curie, M. Becquerel, and those 

 associated with them were influenced by the hypoth- 

 esis that radioactivity is an atomic property of radio- 

 active substances. This hypothesis came to definite 

 expression in 1899 and again in 1902 through Mme. 

 Curie. 



In the latter year the physicist E. Rutherford and 

 the chemist F. Soddy, while investigating the radio- 

 activity of thorium in the laboratories of McGill 

 University, Montreal, were forced to recognize that 

 thorium continuously gives rise to new kinds of ra- 

 dioactive matter differing from itself in chemical 

 properties, in stability, and in radiant energy. They 

 concurred in the view held by all the most prominent 



