The average current may be varied by changing the resist- 

 ance of the electrodes, by varying the source voltage and thus 

 the average interrupted voltage ^ or by both„ Morgan was able 

 to maintain the source CV]_) at 220 volts with increasing 

 average current (l) by decreasing the resistance of the elec- 

 trodeso This is illustrated by the following empirical deter- 

 minations wMch were made with his apparatus (delivering only 

 210 volts at the time)^ using tube-encased carbon electrodes, 

 the exposed surface of which was varied^ and using an on- 

 fraction of Oo25 at 15 r»p.SoS 



V-L(volts) iCamps) V2Cvolts) R - Ir-Jl (ohms) 



The increase m average current was accomplished by 

 decreasing the resistance of the electrodes (increasing 

 their area of exposure), without materially changing either 

 the source or the interrupted voltage, Ihe calculated resist- 

 ance R is mainly that of the electrodes R-, and Rp, 



To demonstrate that the same result could be obtained by 

 varying both the source voltage and the resistance of the 

 electrodes, empirical determinations of V]_ and V^ were made 

 at a constant average current (I) of 3 ampSs and therefore 

 at a constant voltage (Vj) across the electrodes of 0o9ii 

 volts o The resistance or the electrodes was gradually- 

 decreased by changing from small tube-encased carbon rods, 

 to small carbon rods not encased, to large carbon rods 

 wholly immersed, and finally to plates of galvanized iron 

 partially and wholly immersed. In each casej, the source 

 voltage (Vj.) was adjusted to give an average current (l) of 

 3 amps with an on-fraction of 0,25 at l5 ropoS.s 



V^Cvolts) VgCvolts) R ^ Vg/I (ohms) 



210 52 17,3 



160 38 16 



110 21 7 



95 16.5 5o5 



85 12 k 



Since in each of the above determinations j the current 

 (3 am.ps) and the calculated voltage across the electrodes 

 (0,91; volts) remained the same^ the response of fish in the 

 tank should be identicalo If low source voltage is a 

 desirable feature, attempts should be made to procure non- 



73 



