produced from a Gas by High-Speed Cathode Rays. 215 



metallic gauzes, and might cause them to emit /3 rays with 

 very high speed of the same order as that of the primary 

 cathode rays. To test whether the residual currents are due 

 to these fS rays the following experiments were made. 



The innermost gauze Y 1 was covered with a thin celluloid 

 film of a thickness of about 0*0015 mm. (0*2 nag. per sq. cm.), 

 and the current to the electrometer was measured, taking 



Vi=-12, V 2 =-2, V 3 =- 12- v volts. 



V. 



Deflexion 

 cm./20 sec. 



v. 



Deflexion 

 cni./20 sec. 



volts. 

 



1-4 



volts. 

 400 



1-35 



10 



1-35 



600 



1-3 



40 



1-8 



1000 



1-4 



200 



1-35 



2000 



1-35 



The currents are thus practically constant through a wide 

 range of the potential differences up to 2000 volts. Next, 

 the same film was applied to the outermost gauze V 3 , and 

 the currents disappeared. 



According to Lenard's * law of absorption-density, we can 

 assume that the absorption coefficient of celluloid (density 

 1*35 gr./cm. 3 ) for cathode rays is nearly equal to that of 

 paper (density 1*30 gr./cm. 3 ), which is 2690 cm. -1 * for 

 fi rays with a speed of 30,000 volts. Then, by the law of 

 inverse fourth power of velocity f , the coefficient of celluloid 

 for cathode rays with a speed of 10,000 volts (which is the 

 average velocity of the primary cathode rays used in my 

 -experiments) is 2690 x3 4 cm. -1 . Hence the intensity I of 

 the cathode rays of 10,000 volts is reduced to the value I on 

 •emergence from the celluloid film, where 



I = V"AS = j^-33. 



Therefore, with this film we can practically stop all the 

 cathode rays with the velocity of 10,000 volts. The film, 

 however, can be easily penetrated by Rontgen rays, even by 

 those which have a hardness corresponding to 500 volts, as 

 the experiment of E. Laird J showed. Hence the residual 

 currents cannot be attributed to the secondary cathode 

 rays produced by the primary rays or the scattering of the 

 primary rays themselves ; but they are most probably due 



* Lenard, Wied. Ann. lvi. p. 255 (1895). 



t J. J. Thomson, ' Conduction of Electricity through Gases,' p. 379, 

 1906. 



% E. Laird, Ann. d. Phys. xlvi. p. 605 (1915). 



