

from Faraday to J'. J. Thomson. 409 



indefinite time after the substance had been removed from the 

 sunlight, and after the luminosity which properly constitutes 

 phosphorescence had died away ; and he was thus led to con- 

 clude that the activity was spontaneous and permanent. It 

 was soon found that those salts of uranium which do not 

 phosphoresce e.g., the uranous salts, and the metal itself, all 

 emit the rays ; and it became evident that what Becquerel had 

 discovered was a radically new physical property, possessed by 

 the element uranium in all its chemical compounds. 



Attempts were now made to trace this activity in other 

 substances. In 1898 it was recognized in thorium and its 

 compounds;* and in the same year P. Curie and Madame 

 Sklodowska Curie announced to the French Academy the 

 separation from the mineral pitchblende of two new highly 

 active elements, to which they gave the names of poloniumf and 

 radium.}: A host of workers was soon engaged in studying the 

 properties of the Becquerel rays. The discoverer himself had 

 shown in 1896 that these rays, like the X- and cathode rays, 

 impart conductivity to gases. It was found in 1899 by 

 Kutherfordll that the rays from uranium are not all of the same 

 kind, biit that at least two distinct types are present ; one of 

 these, to which he gave the name a-rays, is readily absorbed ; 

 while another, which he named /3-radiation, has a greater 

 penetrating power. It was then shown by Giesel, Becquerel, and 

 others, that part of the radiation is deflected by a magnetic field,1T 

 and part is not.** After this Monsieur and Madame Curieft 

 found that the deviable rays carry negative electric charges, 



* By Schmidt, Ann. d. Phys., Ixv (1898), p. 141 ; and by Ma.iame Curie, 

 Comptes Rendus, cxxvi (1898), p. 1101. 



t Comptes Rendus, cxxvii (1898), p. 175. % Ibid., cxxvii (1898), p. 1215. 



Ibid., cxxii (1896), p. 559. || Phil. Mag. (5), xlvii (1899), p. 109. 



H Giesel, Ann. d. Phys. Ixix (1899), p. 834 (working with polonium); 

 Becquerel, Comptes Rendus, cxxix (1899), p. 996 (working with radium) ; 

 Meyer andv. Schweidler, Phys. Zeitschr. i (1899), p. 113 (working with polonium 

 and radium). 



** Bc-cquerel, Comptes Rendus, cxxix (1889), p. 1205); cx\x (1900), pp. 206, 

 372. Curie, ibid, exxx (1900), p. 73. 



ft Comptes Rendus, cxxx (1900), p. 647. 



