4 IV. F. Holmaii 



other terminal of the condenser, C, were connected to earth. 

 Both the electrometer and the arc system were enclosed in 

 grounded metal cases. Spurious effects were corrected for in 

 all cases by taking observations with the electrode simply 

 screened from the light, other conditions remaining the same. 



The electrode chamber is shown in vertical section and plan in 

 figures 2 and 3. It was designed for testing several metals suc- 

 cessivelv. These were in form of disks, E, mounted on the face of 



a circular glass plate which could be rotated at will about a sup- 

 porting axis of brass by means of the ground joint, D, and key,, 

 K. The electrical connections were made through /, the supjx^rt- 

 ing axis, and the spring brush, B, to the contact, 5. connected by 

 tin-foil strips (placed under the plate) to the cathode, E. The con- 

 nection with the fixed aluminium anode was made through its sup- 

 porting arm, H, and the wire, L. In order to use the metals, E^ 



12S 



