

On the Velocity of Secondary Cathode Bays. 203- 



several thousand volts, Fiirchtbauer * observed, that for 

 positive rays with velocity 2100 to 4500 volts the velocities 

 of most of the 8 rays from a metallic plate were between 

 27 and oO volts, and were independent of the velocity of 

 the primary rays. He found that this was also true when 

 the positive rays were replaced by cathode rays with velo- 

 cities of 1920-4400 volts. He used a magnetic field to 

 determine the velocity of the 8 rays. Campbell f found 

 that the initial velocity of the 8 rays was less than 40 volts, 

 and was nearly independent of the velocity and the nature 

 of the high-speed primary rays — which may be a or j3 par- 

 ticles, — and also of the nature of the metals which emitted 

 the 8 rays. Bumstead J, however, showed that the 8 rays 

 produced by a rays from polonium have velocities which 

 range from to 2000 volts. He pointed out the existence 

 of tertiary rays which were prod need by the 8 rays and had 

 generally slow velocities, and he made use of a plan to 

 eliminate them. Campbell § suggested that the uniform 

 nature of these 8 rays from metals may be due to the ioni- 

 zation of a gaseous layer condensed on the surface of the 

 metals, and not to the ionization of the metals themselves. 



So far as I know, there are not many direct experiments 

 on the nature of the secondary cathode rays ejected from 

 the gaseous molecules themselves. Sir J. J. Thomson II 

 measured the velocity of secondary cathode rays ejected by 

 slow cathode rays. He used a retarding electric field, and 

 determined the maximum velocity possessed by those secon- 

 dary rays whose velocities were sufficiently high to produce 

 an appreciable effect upon the luminosity of the residual 

 gases. Potential differences up to 1500 volts were applied 

 to a Wehnelt cathode. He found the maximum velocity of 

 the secondary rays to be about 40 volts, and that the energy 

 of the rays was independent of the energy of the primary 

 ravs and of the nature of the atom emitting- them. 



The present investigation was undertaken with a view to 

 determine the distribution of velocities of the secondary 

 cathode rays produced from gases by high-speed cathode 

 rays, and to find some relations between this distribution 

 and the speed of the primary rays and nature of the gaseous 

 atom. 



* Fiirchtbauer, Phys. Zeits. vii. p. 748 (1906). 



t Campbell, Phil. Mag. xxii. p. 276 (1911), xxiv.p. 529 (1912), xxiv. 

 p. 783(1912). 



X Bumstead, Phil. Mag. xxvi. p. 233 (1913). 



§ Campbell, Phil. Mag. xxviii. p. 286 (1914). 



|i J.' J. Thomson, Camb. Phil. Soc. xiv. p. 541 (1908). 



