CHEMICAL ELEMENTS AND ATOMS URBAIN 203 



dump the ideas which these discoveries have rendered obsolete. We 

 are indeed fortunate in having witnessed such great events. 



I was especially privileged, for with my own eyes I saw the ele- 

 ment radium born. Pierre Curie was my teacher, and gave me the 

 incomparable honor of his confidence and friendship. I have seen 

 Mme. Curie working like a man with great masses of pitchblende. 

 I saw the first separation of the bromides of barium and radium ; I 

 saw the radiferous crystals shining in the darkness before the spec- 

 trum of radium had been observed. Every Sunday I went with 

 Langevin, Perrin, Debierne, Cotton, and Sagnac into the modest 

 home of Curie which then changed into a kind of intimate academy. 

 There the master with his customary simplicity told his ideas and 

 was as willing to discuss ours. What great problems we debated. 

 The behavior of radium brought into question ideas which had be- 

 come classic. The continuous delivery of energy from radium con- 

 tradicted our fundamental scientific notions. Must we renounce the 

 principle of the conservation of energy, for we then thought that 

 vadium remained unchanged? Were we to admit that radium con- 

 tinuously set free energy without the loss of any part of itself? 

 Does its substance vanish in radiation? And if energy and matter 

 are but different aspects of a same invariant must we give up the 

 principle of the conservation of matter, that great principle of 

 Lavoisier which we have considered the corner stone of chemical 

 science ? 



Pierre Curie desired to avoid destroying such fertile principles. 

 He leaned toward an interpretation which while respecting the 

 work of the past, yet might account for the future. In the end, 

 radium became for him — an hypothesis which has been recently 

 revived by J. Perrin — not a generator but a transformer of energy. 

 This element held captive a yet unknown form of energy and meta- 

 morphosed it in the a, ;8, and y rays. But when Curie, with M"me. 

 Curie, discovered the so-called radioactive deposits, which he called 

 " induced radioactivity," it was evident that radium itself must 

 undergo change. 



When Curie found that radium continuously set free heat we 

 were forced to believe in the failure of the conservation of energy. 

 When his little electroscope automatically charged and discharged 

 itself in the presence of radium, producing work at a constant tem- 

 perature, we had to believe in the failure of Carnot's principle. 

 If we rejected the spontaneous transformation of radium into other 

 elements, we became party to the bankruptcy of thermodynamics. 

 But the emanation (radon), which had the characteristics of a new 

 chemical element, was evidently generated from radium. This ema- 

 nation disappeared spontaneously, little by little, to appear as radio- 



