Cady — On the Energy of the Cathode Rays. 7 



The cathode-current is here only about 1/30 as intense as in 

 Tables II and III, hence the value of i V/Q is also much 

 smaller. The extremely small value of i V/Q when the charge 

 is negative is explained as follows : owing to the conductivity 

 of the path of the rays, a weak current finds its way from the 

 battery used in charging the thermo-element, along this path 

 to the anode. This current is opposed to the cathode-current, 

 thereby reducing the apparent value of the ratio i V/Q. When 

 the thermo-element is positively charged, the ratio is on the 

 other hand greatly increased. 



Measurements similar to the above, made at a pressure of 

 # 012 mm , showed that charging the thermo-element no longer 

 had any influence upon the value of the ratio. These obser- 

 vations on the conductivity of the cathode rays agree well with 

 those of Starke* and Thomson. f 



The attempt was also made to intercept the disturbing cur- 

 rent by means of a grating of several line wires laid over the 

 opening of the Faraday cylinder. This was, however, of no 

 practical assistance, as even at high pressures the effect was 

 very slight. 



The results that have been given show that the observed 

 value of iY/Q was in general too large. The disturbing cur- 

 rent was at times greater than the cathode-current itself, but 

 it was impossible to measure directly its absolute value. It 

 therefore remained to establish the lower limit of the ratio. 

 For this purpose a series of 46 observations was selected, hav- 

 ing a range of pressure from 0*01 to 0'05 mm , of potential from 

 2400 to 5400 volts, and of cathode-'current from 40-10 -7 to 

 - 23 - 10" 7 amp. When arranged in order of decreasing 

 cathode-current, the values of iV/Q showed great irregulari- 

 ties, since the order was without regard to pressure and other 

 conditions. Still a distinct drift in the ratio was evident, espe- 

 cially when the observations were divided into five groups and 

 the average values taken : 



ressure. 



rlO 7 Amp. 



iV/Q 



0-041 



19-6 



1-32 



0035 



7-41 



0-97 



0-026 



4-29 



0-85 



0-033 



2-02 



0-84 



0-023 



0-49 



0-83 



From this it is evident that when the cathode-current 

 decreases to the fortieth part of its original value, the ratio i V/Q 

 is changed by only 38 per cent. This at least makes it seem 



* H. Starke, Wied. Ana., lxvi, p. 52, 1899. 



f J. J. Thomson, Phil. Mag , xliv, p. 293, 1897. 



