542 Prof. J. J. Thomson on the Charge of Electricity 



In the preceding investigation we have assumed that the 

 nuclei producing the cloud are those which cause the con- 

 ductivity, and are produced by the rays ; there is, however, 

 a small cloud produced even when no rays are on ; if we 

 assume that the nuclei which produce this cloud are still 

 active when the rays are on, it follows that in the preceding 

 investigation we have over-estimated the number of ions 

 engaged in carrying the current by the number of nuclei 

 present when the rays are not passing through the gas. As 

 the cloud fell three times faster when the rays were not on 

 than it did when the rays were on, the number of nuclei 

 when the rays are not on is to the number when the rays 

 are on as 1 is to 3*, or as 1 : 5*2 ; hence 1/5*2 of the nuclei 

 are not engaged in carrying the current, so that to get the 

 charge on the ions we must increase the value just given in the 

 ratio of 1 + 1/5*2 to 1 ; this makes 



e=7*4xl0- 10 . 



The results of other experiments on air are given in the 

 following table : — 



Expansion. 



Temp. 



Current 



through 



gas. 



Kate of fall 

 of cloud. 



e 



uncorrected for 



nuclei present 



without rajs. 



e 

 corrected. 



1-36 



16 



•243 E 



•09 



6-7 XlO- 10 



7'6 



1-36 



16 



•133 E 



•147 



64 



7-2 



1-38 



16 



•143 E 



•156 



73 



8-4 



1-36 



16 



•196 E 



•104 



6-3 



7-4 



1-36 



16 



•115 E 



■125 



5-0 



6-0 



The mean of these values and the one previously obtained 

 is 



e—l'Z x 10~ 10 electrostatic units. 



Another correction has to be made to allow for the conduc- 

 tivity of the walls of the vessel A due to the film of moisture 

 with which it is coated. Though the walls are insulated from 

 the aluminium plate at the top of the vessel, and there is no 

 leak between them when the rays are not passing through the 

 glass, the conductivity of the glass when the rays are on 

 causes the current to travel partly from the aluminium plate 

 and along the walls of the vessel instead of wholly through 

 the air as has been assumed in the calculations. To estimate 



