To face page' 136, 



FIG. 37. Observer's Table. At left, the window, lever for raising shields, and water ther- 

 mometers ; on table at left is the rheostat, above it the valves for controlling cooling 

 water, and in the center of table the mercury switch. Incidental electrical connec- 

 tions and instruments are shown on right of table. The galvanometer scale is imme- 

 diately above table. 



