the Corpuscular Hypothesis of the 7 and X Rays. 387 



plate *, but very many more are found on the side of: the 

 plate from which the 7 rays emerge than on the side through 

 which they enter. In fact experiment shows that their dis- 

 tribution is just such as should be found it', when they are 

 first formed, they simply prolong the line of motion of the 

 7 rays, and if their subsequent movements are due to the usual 

 scattering which ft rays undergo. Cookseyt has shown 

 that the same lack of symmetry is to be found in the cathode 

 radiation which is caused by X rays. 



It is also found that the speed of the ft ray, which is caused 

 by a 7 ray, is independent of the nature of the atom in which 

 it originates, but is directly connected with the quality of 

 the 7 ray. Again the parallel effect is to be observed with 

 X rays, as is evident from the work of Dorn, Lines, and 

 others, who have made it clear that the speed of the cathode 

 rays which originate when X rays fall upon atoms depends 

 rather on the nature or quality of the X rays than on the 

 kind of atom. But the most accurate and complete proof's 

 of these principles have been recently given by Beatty J and 

 by Sadler §. 



These facts are of fundamental importance when we come 

 to discuss the source from which the /3-ray energy is drawn. 

 If it comes from the atom, as was first supposed, we have a 

 trigger effect : the 7 ray is to be considered as precipitating 

 an explosion ||. But if this were the case we should expect 

 (1) that the direction of motion of the shot, viz. the ft ray, 

 would have no connexion with the direction of motion of the 

 7 ray which merely pulled the trigger of the gun ; (2) that 

 the speed of the ft ray would not depend on the quality 

 of the ray, but on some property of the atom corresponding 

 to the charge in the gun. The actual conditions are exactly 

 the reverse. If we examine the alternative hypothesis, viz. 

 that the energy of the ft ray is brought to it by the 7 ray, and the 

 atom is merely the cause of a transference of energy, we find 

 a perfectly satisfactory explanation. The momentum of the 

 electron is a persistence of the momentum of the y ray, and 

 its energy is derived from the ray ; the electron, therefore, 

 continues the line of flight of the 7 ray with a speed which 

 has nothing to do with the atom to which the transformation 

 is due, and depends entirely on the quality of the 7 ray. 



* Brasrg and Madsen, Trans. Ilov. Soc. of South Australia, Jan. and 

 May 1908 ; also Phil. Mag. May and Dec. 1908. 

 t < Nature/ April 2, 19J8. 

 X Proc. Camb. Phil. Soc. vol. xv. pt. v. p. 416. 

 § Phil. Mag. March 1910. 



|| ' Conduction of Electricity through Gases, 1 2nd ed. p. 320. 



2 U 2 



