PIERCE. — CRYSTAL RECTIFIERS FOR ELECTRIC CURRENTS. 327 



potential current through the tube was supplied by Professor Trow- 

 bridge's 40,000 volt storage battery, which he kindly placed at my 

 disposal. Usually only 20,000 volts of the battery were employed, 

 and this was controlled by means of a running-water rheostat in series 

 with the battery and the tube. 



TABLE III. 



Current- Voltage Values for the Molybdenite Rectifier. 



Larger Currents. 



The cathode beam in the tube produced a luminescent spot on the 

 fluorescent screen at 0. The -electromagnets, through which the cur- 

 rent to be oscillographed was sent, were placed above and below the 

 Braun's tube at MM. Therefore the deflection of the spot was in a 

 horizontal line perpendicular to the plane of the Figure. The photo- 

 graph of the moving luminescent spot was taken on a sheet of bromide 



