voltage (maintained by Morgan at 220 volts) may be varied 

 between limits (about ^0 to 250 vclts) by means of a rheostat 

 in series with the generator field coilso The voltmeter (V-j_) 

 measures the source voltage „ The voltmeter (V^) measures 

 the voltage after interruption, an average value which is a 

 fraction (approximately the on-fraction) of the source or 

 peak voltage It also measures the voltage at, but not between., 

 the electrodes if it may be assumed that the resistance of the 

 rever sing-polarity switch and the lead wires to the electrodes 

 is negligibleo The ammeter (A), which may be placed anywhere 

 in the circuit, measures the average interrupted current (I), 

 which again is a fraction (approximately the on-fraction) jf 

 the source or peak current,, Ihe interrupter is a motcr-driven 

 disk which may be changed to give the desired "on-off" ratio o 

 The electrodes have unknown resistances (R^ and Rp) wluchj, 

 with tube-encased carbon electrodes, vary with the extent oi 

 exposure to seavrater and the extent of polarizing by gas 

 bubbles which are generated during a current flow, Ihe 

 electrodes are immersed at either end of the tank of seawater, 

 Ihe seawater has a resistance (R3) which may be calculated 

 roughly as ,p 



R3 ^ k ~-^ Oo0^23 -^Y" " 0,3138 ohms J 



where k is the specific resistance of seawater at a chlorinity 

 of 19 PoPofflo and a temperature of 2.5° Co, L is the length of 

 the water column (feet) and Ar., is its area (square feet). 

 The apparatus and hook-up described above are identical with 

 those used by Morgan^ except for the insertion of the voltmeter 

 (V2) across the line after interruption o 



Of the various voltage measurements which might be made^, 

 the average voltage (V^) across the electrodes is the only one 

 of importance from the point of view of the reaction of the 

 fisho This cannot be measured directly without a special volt- 

 meter, but it may be calculated according to Ohm's Laws 



V3 ^ I'>R3 



knowing the average current (l) and the resistance of the 

 column of seawater (Rj) = "^^^s the following values may be 

 obtaineds 



I (amps) V3 (volts) 



1 o7^ 



2 O06J 



3 0.9h 

 h lo26 

 5 lo57 



etco 



7? 



