136 



THE UNIVERSITY OF OKLAHOMA 



of the current in one direction but not in the other. If a 110-volt 

 direct current be sent through such a cell making the aUnninum 

 plate the cathode there is practically no resistance offered by the 

 cell but when the aluminum plate is made the anode an entirely 

 different result is obtained. At the instant the circuit is closed — 

 if it is a fresh-cell and there is little resistance in the circuit — the 

 current rushes through with a strength of several amperes but 

 drops to a fractional part of an ampere in three or four seconds. 

 With the dropping of the current there is a simultaneous rush of 

 the voltage from less than 10 volts up to a value near 80, and 'n 



Figure 8 



less than a minute it reaches aim.o.-t 110 which is practically the 

 same voltage it would show on open circuit. 



This phenomenon was first observed by Wheatstone about sev- 

 enty years ago but no use was made of it until approximately fifty 

 years later when PoUak and Groetz, each working independently, 

 conceived the idea of using it to convert an alternating current into 

 a direct current. With a single cell one alternation is eliminated 



