due to temporary exposure to <y rays. 127 



and at neither speed, was there any certain indication that the 

 ionization in the first cylinder was greater when the disc was in 

 motion than when it was at rest. A false positive result was 

 sometimes obtained owing to the aluminium leaf becoming slightly 

 torn near the edge of the window, and allowing ionized air to 

 enter from outside, a greater quantity when the air was in motion 

 than when it was at rest. This difficulty, however, was easily 

 overcome by care in making the window. A second difficulty was 

 that the rotation of the disc, notwithstanding its independent 

 support, had a tendency to disturb the balance slightly, probably 

 by causing a slight motion of the compensating cylinder. This 

 effect however usually persisted when the next observation was 

 taken with the disc at rest, as will be seen from some readings 

 which are given below as examples. The results quoted are a 

 fair sample of the measurements which were taken under favour- 

 able conditions ; there were many others which were vitiated by 

 disturbing causes of one sort or another. The numbers give the 

 potential in volts acquired by the gold leaf in 10 minutes. 





Copper. 



Slow speed. 





Disc at rest 





Disc in motion 



(1) 



0-095 





— 



(2) 



— 





0-08 



(3) 



0-067 





— 





Lead. 



Slow 



speed. 





Disc at rest 





Disc in motion 



(1) 



0-22 





— 



(2) 



— 





0-28 



(3) 



0-26 





— 



W 



— 





0-32 



(5) 



0-28 





— 





Tin. 



Slow 



speed. 





Disc at rest 





Disc in motion 



(1) 



0-08 





— 



(2) 



— 





0-21 



(3) 



0-23 





— 



(4) 



— 





0-33 



(5) 



0-40 





— 



BLOTTrNG-PAPER SOAKED IN 



Uranium Nitrate. Slow speed. 





Disc at rest 





Disc in motion 



(1) 



0-03 





— 



(2) 



— 





0-07 



(3) 



0-09 





— 



