RONTGEN RAYS 323 



the velocity which the original cathode ray owed to the electric 

 intensity in the discharge tube. The heat energy, of course, 

 may be derived wholly from those encounters in which the ray 

 is merely absorbed, and in which the conditions do not favour 

 a transformation of the ray, with a transfer of energy without 

 any degradation. 



As both primary and secondary cathode rays are hetero- 

 geneous, it may be, however, that a secondary ray may owe its 

 velocity to an X ray generated by a slightly faster primary 

 cathode ray, the small difference in the energies being that lost 

 in the two transfers. Thus the mean speed of the secondary 

 beam of rays would be a little lower than that of the primary, 

 but the difference might not be marked. 



In the discontinuous pulse theory, one has to assume that 

 the whole of the energy of the primary cathode ray goes into 

 a single energy bundle, which in its turn liberates one, and 

 only one, electron, to which it gives up all its energy. Other- 

 wise we cannot, without calling in the aid of atomic energy, 

 provide for the almost equal velocities of the primary and 

 secondary cathode rays. 



It may be noticed that the pulse theory demands that the 

 thickness of the pulse or the size of the bundle must not be 

 greater than the diameter of a corpuscle ; if it is thicker, only 

 a portion of the energy of the cathode particle is converted into 

 radiant or pulse energy. Now other considerations indicate a 

 value for a diameter of the corpuscle of about io~ 13 cm. Apropos 

 of this we may record the calculations of Wien (1907) and Stark 

 (1908), who, working on extensions of Planck's theory of radia- 

 tion, and supposing that no energy is degraded in a primary 

 or secondary transformation, derive values of 6*8 x io -9 and 

 6 x io~ <J cm. respectively for the thickness of a pulse. 



An ether pulse must accompany an alteration in the motion 

 of a charged particle, if the change is sufficiently sudden. Wien 

 (1905) and van der Waals, jun. (1907), calculate that if the 

 whole of the energy of a cathode ray is to be transformed into 

 pulse energy, it must be completely stopped in a space of about 

 io -10 cm. Thus these different calculations are based on assump- 

 tions and data which yield values of more nearly atomic than 

 corpuscular dimensions. 



As regards the neutral pair theory, it is difficult to understand 

 the mechanism by which a cathode ray entering an anticathode 



