19:2:i] The Search for the Ultimate Atom 37 



over a good many years. In 1883 he began the study of the nature 

 and constitution of the rare earths. From his studies of the spectra 

 of yttrium he concluded that there was an actual splitting up of 

 the yttrium into more elementary substances, also he formulated the 

 hypothesis that all the elements have resulted from a primary sub- 

 stance which he termed protyle. 



Not only directly but also indirectly was the Crookes tube a 

 potent factor in the establishment of the electronic theory. It was 

 while working with a Crookes tube in 1895 that Roentgen discovered 

 the X-rays which have been so efficient as an aid in establishing this 

 theory. Becquerel was impressed with the similarity in appearance 

 of the phosphorescence produced by X-rays on the glass of the 

 vacuum tube and the phosphorescence produced in some ordinary 

 substances by sunlight. 



He thought that possibly these would emit radiations similar to 

 X-rays. Prompted by this idea, in 1896 a few months after the 

 discovery of X-rays he placed several substances wrapped in paper 

 beneath a photographic plate. Of these the only one that acted on 

 the plate was a salt of uranium. He subsequently found that this 

 property of affecting a photographic plate was common to all the 

 salts of uranium and that it was possessed by the element itself. 

 Moreover, he found that this action was a spontaneous one, that it 

 made no difference whether uranium and its compounds were ex- 

 posed to sunlight or kept wholly in the dark. This was the begin- 

 ning of radioactivity and the study of radioactive substance. In 

 this study there have been numerous investigators. Becquerel ex- 

 tended his studies further and later found the ratio of — for the 



m 



beta (/8) rays of radium and also their velocity. The ratio of — 

 he found practically the same as that previously determined by J. J. 

 Thomson for cathode rays. He found, however, that they had vary- 

 ing velocities some moving much faster than others. These dif- 

 ferences in the velocities of the beta (/?) rays furnished Kaufmann 

 an opportunity to test the electromagnetic theory of mass — that the 

 mass of an electron is due, wholly or in part, to the fact that the 

 electric charge is in motion. The findings of Kaufmann were entirely 

 in harmony with the theory, since — decreased as the speed in- 

 creased. 



