120 



BULLETIN OF THE BUEEAU OF FISHERIES 



not have any effect. A very accurate record was kept of the fish killed during this 

 test. The hatchery attendants were instructed not to remove any dead fish from 

 pond No. 12 without having them properly recorded. For the entire period of 11 days 

 (this includes August 17, the first day of the test, which was eliminated from the 

 10-day continuous run by a short circuit in the temporary alternating-current supply 



VAKMTION OF MINIMUM VOLTAGE. GRADIENT WITH ELECTRODE SPACING 



FOR 



PARALLEL CYLINDRICAL ELECTRODES 



IMMERSED IN WATER OF ANY UNIFORM RESISTIVITY 



VOLTAGE ONE VOLT TO NEUTRAL OR TWO VOLTS BETWEEN ELECTRODES 



VOLTAGE GRADIENT MIDWAY BETWEEN E LECTRODES ALONG LINE OF CENTERS 



ffi VOLTASt GRADIE.NT MIDWAY eETWEEn JglNCH STAMOARO PIPE ELECTR0BE3 



1 „ .... 



2 m n h •• 



3 .> .. •• " 

 _6. 



FlQ. 15 



Une on August 18), from August 17 to August 27, inclusive, 29 fish were killed by the 

 electric screen, or less than 0.2 per cent of the 15,000 fish in pond No. 12 — a neghgible 

 number. The maximum number of fish killed in one 24-hour day was six; on two 

 days no fish were killed; and the average number killed per day for the 11-day period 

 was 2.64. By the use of larger-diameter electrodes (thereby obtaming a more uni- 

 form voltage gradient) even this small number of fish killed could have been reduced. 



