WORK OF HENRI BECQUEREL BROCA. 781 



the cathode rays as shown by Sir W. Crookes and Edmond Becquerel. 

 He compared the chemical jDhenomena produced by the cathode raj'S 

 and those which the Curies had observed wuth the action of radium 

 upon glass. 



It was but a step to Becquerel's examination of the effect of the 

 magnetic field upon the emanation. Giesel, Meyer, and Schweidler 

 had already obtained some results along that line, but they were 

 imknown to Becquerel. Becquerel's observations, when completed, 

 w^ere more profound, more fertile than those of his predecessors. He 

 observed the important fact that the radiation, deviated like the 

 cathode rays by the magnetic field, suffers a dispersion. This showed 

 that the emanation is composed of electrons having different veloci- 

 ties. At the same time, working with an electrometric method, the 

 Curies showed that in the emanation from radium there is an unde- 

 viated part much more absorbed than the other mys, thus giving a 

 new distinction between the a and ft ra3^s of Rutherford. Polonium 

 according to Becquerel gives only the nondeviable rays. But at 

 the same time Villard showed that in the nondeviable bundle there 

 exists, besides the very absorbable a rays, a set, extremely transmissi- 

 ble, which he called the " y rays," and which are identical with the 

 Rontgen or X rays. 



The remarkable studies of J. J. Thomson on the cathode rays re- 

 corded that from the trajectories of the electrons in a known magnetic 



field we may determine the quantity — , where m is the mass of the 



electron charged with a quantity of electricity e, and having the ve- 

 locity V. The trajectory of the rays discharged normal to the field 



should be a circle whose radius R = 77-, where H is the intensitv of 



He 

 the field. It was necessary to see if the radium raj^s gave trajectories 



whose radius equaled —^ analogous to cathode ravs. Exj^eriments 

 e 



showed this to be true and that all the preparations of radium or its 

 salts gave the same kinds of rays. It served also to show that the dis- 

 persion in the magnetic field could serve for the study of the pene- 

 trability of the various emanations, for the more deviable the more 

 penetrating are the rays. The images obtained by placing various 

 screens separating a photographic plate from a morsel of radium in 

 the bottom of a lead trough, and all placed in a magnetic field, al- 

 lowed, by means of the images upon the plate, a determination of the 

 limits to which the emanations penetrated the screens. Moreover, 

 the radii of curvature were easily calculated. Knowing the field H, 

 the products RH could be easily deduced. These products, equal to 



— , la}^ between 637 for copper and 3082 for lead. Admitting veloci- 



e 

 ties analogous to those of the cathode rays, the values, — , could be ap- 



e 



