the Method of its Transmission. 103 



Plates 1*30 cm. apart. 



JEo+E,. 



E -E r 



Alternations 

 per sec. 



P- 



K. 



75 



50 



57 



•17 



1-7 



152 



101 



57 



•27 



1-25 



225 



150 



57 



•38 



1-17 



300 



200 



57 



•44 



1-24 



The value o£ K is given in cms. per sec. for a potential- 

 gradient of 1 volt per cm. 



For the last example, since the carrier travelled over a dis- 

 tance greater than 1*30 cm. during each half alternation, a 

 modified form of the equation was necessary to calculate the 

 velocity. 



The value 1*6 cm. per second for 50 volts is too high for 

 the reasons explained above. 



E +E t . 



E — E r 



273 



207 



300 



200 



Plates 2 cms. apart. 







Alternations 



P- 



K. 



per sec. 





44 



•37 



1-47 



53 



•286 



1-45 



An average value of the velocity from a large number of 

 alternations for different distances, voltages, and speed of 

 alternations was about 13 cm. per see. for atmospheric 

 pressure and temperature. 



This velocity is not very different from the velocity of the 

 positive ion produced by Rontgen or Becquerel rays. The 

 most accurate determination of this velocity by Zeleny* gave 

 a value of 1*37 cm. per sec. for dry air. 



§ 5. Increase of Excited Radiations with Time. 



In the course of these experiments a remarkable effect was 

 observed. It was found that a plate which has been exposed 

 a short time in the presence of thoria emanation, after being- 

 removed, gradually increased in radioactive power for several 

 hours. The amount of increase varied with the time of 

 exposure to the emanation, but in short exposures it increased 

 to three or four times its initial value. For exposures of 

 several hours the effect is not so marked, and is difficult to 

 detect after a day's exposure. 



The following tables illustrate the results obtained. 



* Phil. Trans. Roy. Soc. (1900). 



