WOEK OF HENRI BECQUEKEL BROCA. 783 



To Becquerel it seemed due to an augmentation of the mass, to Ruth- 

 erford to a diminution of the velocity. 



Becquerel found that polonium gives rays that are identical with 

 the a rays of radium. An exhaustive study of uranium, even in 

 vacuo, disclosed no a rays, but it was found to emit very deviable (3 

 rays — that is, rays of small velocity. 



The beginning of these studies had shown the existence of second- 

 ary rays produced by the bombardment of another body by the 

 Becquerel rays. Further study showed that all radium rays do not 

 possess this property. The most rapid corpuscles traverse aluminum 

 and suffer no modification. Those for Avhich RH=3.43G are the first 

 to suffer change and produce the secondar^^ rays after passing through 

 the aluminum. AMien liH< 1.500 they are completel}^ absorbed by 

 the aluminum and give no emission. The secondary rays are deviated 

 like the j^rimary in an electric field. 



It was these secondary rays which produced the intense impression 

 on the photographic plates of Becquerel. The very penetrating 

 emanation traversed the lead, producing the secondary rays which 

 then affected the plate. These rays produce the augmentation of the 

 impression along the screen hit by the Becquerel rays. These experi- 

 ments remade with polonium showed that in time the secondary rays 

 due to mica indicate a much more penetrating emanation than that 

 ordinarily noted from polonium. 



Becquerel studied the transformation of white into red phosphorus 

 under the influence of these emanations and showed that the slightly 

 penetrating rays produced the essential part of the action. The a 

 rays could not be tried because of the necessity of protecting the 

 radium. 



The fertile success of the ionization theory made it interesting to 

 see whether analogous phenomena took place in solid dielectrics. J. J. 

 Thomson showed that it occurred with the X rays. Becquerel 

 showed that liquid or solid paraffin became conducting under the 

 action of the rays. That the action continued constant in the same 

 apparatus during a year indicated that it took place even when the 

 paraffin had reached its permanent state. 



At the time of these discoveries the Curies were bringing to notice 

 induced radio-activity, and Rutherford, the emanation of radium 

 with its curious properties, the exhaustion of the solution which gave 

 the emanation, and the recovery of the radio-activity after a certain 

 time. Thorium had an emanation of its own. None could be isolated 

 from uranium, and j^et Becquerel showed that certain ])henomena 

 appeared to indicate one. Sir W. Crookes showed that by fractional 

 crystallization of the nitrate of uranium in ether the foreign matter 

 became reactive, the nitrate less and less so. He attributed this to a 

 new body which he called uranium-X. Becquerel showed that these 



