electrical weir lead wires without cutting into or connecting directly 

 to these wires. This instrument also contains a voltmeter circuit 

 which may be used to measure voltages across the electrode rows of the 

 weir. 



The power consumption of the uniform field barriers is the 

 product of the current in amperes (in the ungrounded line to the weir) 

 and the voltage across the weir. In the incremental field barriers, 

 two power measurements must be made; one of the power supplied to the 

 upstream half of the weir and one of the power supplied to the down- 

 stream half of the weir. The ••upstream" power is the product of the 

 amperes measured in the "A" row of electrodes and the voltage measured 

 between rows "A" and "B". "Downstream" power is determined in a similar 

 manner; it is the product of "C" row amperes and the voltage between 

 rows "B" and "C". The total power input to the weir is then the sum of 

 the "upstream" power and the "downstream" power in watts. Power con- 

 sumption will be found to vary directly with such factors as applied 

 voltage, water level, electrolytic content of the water, and the ratio 

 of water resistivity to stream bottom resistivity. 



Voltage gradients . — Readings of water voltage gradients taken 

 within the energized field of an electrical weir provide the most reli- 

 able measure of its effectiveness, once the blocking or lethal voltage 

 gradient has been established. Voltage gradient measurements at the 

 various experimental sites were made with a high impedance vacuum tube 

 voltmeter, General Radio Model No. 727-A, used in conjunction with a 

 specially designed water voltage gradient probe (Figs. Ik and 1$) . This 

 instrument permits the operator to determine the direction of maximum 

 current flow through the water medium at any point, and in addition, the 

 R.M.S. value of the voltage gradient producing this current flow. The 

 measuring electrodes of the voltage gradient probe are spaced three inches 

 apart; therefore, readings observed on the vacuum tube voltmeter are 

 divided by three to obtain the voltage gradient in volts per inch. This 

 instrument was used extensively to measure voltage gradients produced in 

 each of the various tests that involved changes in voltages, electrode 

 diameter, or electrode spacing. 



In general, between 9 and 20 readings were taken in the test 

 of an electrical weir depending on its type. At the Carp Creek and 

 Hibbards" Creek devices, the most significant locus of voltage gradient 

 measurement was considered to lie at the midpoint of a line perpendicular 

 to both the lateral, ground electrode and the line of suspended electrodes 

 and passing midway between two adjacent suspended electrodes. The aver- 

 age value of three such readings, expressed in volts per inch, constitutes 

 the "arbitrary minimum voltage gradient" subsequently referred to for this 

 type of array. In the multiple-row, suspended electrode systems such as 

 those operated in the Kewaunee River and Squaw Creek locations, the point 



2U 



