in Gases to the Contact Potential Series. 389 
discharge-tube. A hard rubber disk, D, studded with brass 
rivets C, and fixed to the circular plate, served to complete 
Fig. 1. Fig. 2. 
G aS 
the {electric cireuit from F through the metal collar and 
attached spring-brush B to the tinfoil strip leading to its 
corresponding electrode E. By this device all electrodes, 
with the exception of the one in use, were isolated from the 
Phil. Mag. 8. 6. Vol. 8. No. 45. Sept. 1904. 21 
