74 THE KINGDOM OF MAN 



particular sample of uranium salt has shown no sign of 

 diminution since this discovery. The emission of pene- 

 trating rays by uranium was soon found to be independent 

 of its phosphorescence. Phosphorescent bodies, as such, 

 do not emit penetrating rays. Uranium compounds, 

 whether phosphorescent or not, emit and continue to 

 emit, these penetrating rays, capable of passing through 

 black paper and in a less degree through metallic copper. 

 They do not derive this property from the action of 

 light or any other treatment. The emission of these 

 rays discovered by Becquerel is a new property of 

 matter. It is called ' radio-activity,' and the rays are 

 called Becquerel rays. 



From this discovery by Becquerel to the detection and 

 separation of the new element radium is an easy step in 

 thought, though one of enormous labour and difficulty 

 in practice. Professor Pierre Curie (whose name I can- 

 not mention without expressing the grief caused to all 

 men of science by the sad accident by which his life 

 was taken) and his wife, Madame Sklodowski Curie, in- 

 cited by Becquerel's discovery, examined the ore called 

 pitch-blende which is worked in mines in Bohemia and 

 is found also in Cornwall. It is the ore from which all 

 commercial uranium is extracted. The Curies found 

 that pitch-blende has a radio-activity four times more 

 powerful than that of metallic uranium itself. They at 

 once conceived the idea that the radio-activity of the 

 uranium salts examined by Becquerel is due not to the 

 uranium itself, but to another element present with it 

 in variable quantities. This proved to be in part true. 

 The refuse of the first processes by which in the manu- 

 facturer's works the uranium is extracted from its ore, 

 pitch-blende, was found to contain four times more of 

 the radio-active matter than does the pure uranium. 



