324 SCIENCE PROGRESS 



can there pick up a positive electron, and without the assistance 

 of atomic energy emerge with its direction reversed, or nearly so, 

 and with a velocity much the same as when it entered. Neither is 

 it easy to imagine an electric field which, prevailing in an atom, 

 can dissolve a doublet, retain the positive and yet not affect the 

 velocity of the negative, which goes on with the speed of the 

 doublet. The part played by the positive component seems a 

 little obscure. 



It must be admitted, however, that Prof. Bragg's theory of 

 the close resemblance between the /? and the 7 rays — the differ- 

 ence being merely one of charge — has several experimental 

 results in its favour. For instance, both (3 and 7 rays produce 

 secondary cathode rays with nearly equal velocities, and it does 

 not seem reasonable that, while in the case of the /3 rays the 

 secondary radiation consists largely of scattered primary, it 

 should, in the case of the 7 rays, be atomic in its immediate 

 origin, as the pulse theory insists. 



In reviewing the subject, the mind recalls two analogues to 

 the present position in the history of physics. First when 

 experiment was needed to discriminate between the undulatory 

 and the Newtonian emission theory of light. And again when, 

 in more recent years, the English and Continental schools were 

 at issue as to the nature of the cathode rays. 



Now, as then, the choice lies between a material particle and 

 an immaterial disturbance, and once more it is for experiment 

 to decide. 



Literature 



Rontgen, Wied. Ann. 64, p. 1, 1898. 



Emission of Rontgen Rays 



RONTGEN, Wiirzburg Stake? scher Verlag. Marz 1896. 



Kaye, Proc. Camb. Phil. Soc, 14, p. 236, 1907 ; Phil. Trans. Roy. Soc. A, 1908. 



Distribution of Intensity about a Rontgen Ray tube 



/Ham., Amer. Assoc. Adv. Science, Chicago, Jan. 1908. 

 \BORDlER, Archives PEcole Medicate, 16, p. 299, April 1908. 



Absorption and Transmission of Rontgen Rays 



Benoist and HuRMUZESCU, Compt. Rend., Fev. 17, 1896. 



BENOIST, Compt. Rend., Jan. 18, 1897 ; Journ. de Phys. (3) 10, p. 653, 1901. 



Walter, Ann. der Phys. 17, p. 561, 1905. 



Adams, Amer. Acad. Arts and Sciences, 42, p. 671, 1907 ; Phil. Mag. 13, p. 576, 



1907; Amer. Assoc. Adv. Science, Jan. 1908 

 Kaye, Proc. Camb. Phil. Soc. 14, p. 236, 1907 ; Phil. Trans. Roy. Soc. A, 1908. 



