1879.] Electrical Insulation in High Vacua, 349' 



plate of mica was longer and wider than the gold leaves, and was con- 

 nected with a small piece of iron wire, capable of moving up and 



Fig. 2. 



down a tube sealed into the top of the bulb. By means of an outside 

 magnet the mica plate could thus be lowered between the gold leaves 

 or raised out of their way, as desired. The tube was exhausted to 

 about the millionth of an atmosphere, the mica plate being held quite 

 above the leaves. One side of the bulb was then heated, and the 



Fig. 3. 



