CHAPTER III. 

 DISCOVERY OF RADIO-ACTIVE ELEMENTS. 



Radio-activity, a new property of matter, had been dis- 

 covered, but whence its source? "The metal uranium it- 

 self," you say, " since it gives off the rays." Yes; but still a 

 doubt a little, tiny doubt remained. Was it not possible 

 that the power of emitting rays, the radio-activity, was due 

 to some small jimpurity present in the uranium? That doubt 

 was the key which" unlocked the door to a roomful of other 

 discoveries. 



It arose in the minds of two investigators who had been 

 interested observers of Becquerel's work, M. Pierre Curie, 

 Professor of Physics in the School of Physics and Industrial 

 Chemistry at Paris, and Madame Sklodowski Curie, his wife. 

 They resolved to investigate the ray-emitting power of pitch- 

 blende, the parent substance from which all uranium is ex- 

 tracted. To their gratification they discovered that selected 

 specimens of pitchblende possessed a radio-activity four 

 times greater than metallic uranium itself (Figs. 23 and 34). 

 Nature never insults us by caprice, and, consequently, we find 

 the Curies saying: "It becomes then very probable that if 

 pitchblende has so strong an activity it is because the min- 

 eral contains, in small quantities, a substance wonderfully 

 radio-active, different from uranium or any of the simple 

 bodies actually known. 



" We proposed to ourselves to extract this substance from 

 pitchblende and we have ; in fact, been able to prove that it 

 (90) 



