242 Electrical Insulation in High Vacua . [March, 
top of the bulb. By means of an outside magnet the mica 
plate could thus be lowered between the gold leaves or raised 
Fig. 2- 
out of their way, as desired. The tube was exhausted to 
about the millionth of an atmosphere, the mica plate being 
Fig. 3. 
held quite above the leaves. One side of the bulb was then 
heated, and the leaves permanently charged by means of the 
