Two experiments (C and D of table 11) were performed using 

 fresh mineral oil floating on the mercuryj and an on-fraction 

 of O„083o At Oo5 amps, 12 out of 18 trials with three ahole- 

 hole were positiveo At 1 anps 21 out of 26 trials (81 percent) 

 were positive « The latter results are comparable with those 

 obtained by Morgan at 3 asaps with an on -fraction of Oo25 

 Ctable 12 -D), Unfortunately m the present experiments there 

 is no guarantee that the on-^fraction was maintained exactly 

 at O0O835 nor that the current was maintained exactly at loO 

 anpsc However, the results indicate an additional saving of 

 power by further reduction of the on-fractiono 



DISCUSSION 



The regression of minimal current for total (or near- 

 total) response on on-fraction is shown in figure 21 for both 

 Morgan's results and those of the writero The present results j 

 although meager^ indicate the continuance of the downward 

 trendo They shoiLLd be checked with more fish and better equip- 

 ment ;, and extended to include still smaller on-fractionso 



It may be noted that at 2 anps average current and IS 

 ropoSoj the on-period is Ool^l/l^ " OoOl seconds^ or 10 milli- 

 secondso It is interesting to note that according to Houston 

 (19U9)j DTo Konrad Kreutzer of Germany apparently used an on- 

 period of about 2 milliseconds, with a frequency which varied 

 (2 to 20 r,p,s„) depending on the natural wriggling frequency 

 of the particular fish. The present results are therefore in 

 agreement with those of Kreutzer in indicating the desirability 

 of using a short on-fraction„ It will be interesting to deter- 

 mine if 2 milliseconds is the optimum value for positive 

 attraction at minimal current o The present results do not 

 agree with those of the Cooperative California Sardine Research 

 program (Anon 19$0)j in which greater response was found with 

 a longer on-fractiono 



It seems useless to conduct further experiments with the 

 present apparatus., Rather j efforts should be made to invent 

 or perfect an interrupter which is rapid in action^ free from 

 arcings and provides an adjustment for varying the "on~off" 

 ratio. This might be electronic or mechanicals, Both have 

 been used by Kreutzer (Anono 1951) hut in his work the elec- 

 tronic switch was to be replaced by an inpulse switchj developed 

 by Siemens Werke of Germanyj wPd-ch "is quite compact^ is com~ 

 pletely mechanicalj and is said to have an accuracy of l/lOOjOOO 

 of a secondo" 



81 



