162 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



as might have been expected in the most " halistatic " known 

 area of the ocean. 



These hauls were taken miles apart at considerable intervals 

 of time ; the question next arises whether simultaneous or 

 almost simultaneous hauls taken through closely adjacent 

 bodies of water would show a greater degree of uniformity. 

 Hensen made a series of experiments, also discussed by Schufct, 

 in which he hauled the same net twice in rapid succession in 

 as nearly as possible the same body of water, on forty occasions, 

 and eight times in succession once, and found that the average 

 error was about 13 per cent. 



In all such work at sea it is obvious that much depends 

 upon the weather, the conditions under which the ship is 

 working and the care taken in the experiment. With the view 

 of getting further evidence from a new series of data, taken with 

 all possible care under favourable conditions, I carried out a 

 number of similar experiments at Port Erin during several 

 months in spring, summer and autumn of 1920. They con- 

 sisted of a series of four to six " successive " (that is, as nearly 

 as possible simultaneous) vertical hauls taken with the Nansen 

 net of No. 20 silk. On each of the seven occasions (four in April 

 and one each in May, August and September) a day was selected 

 when the weather was favourable and a time when it was 

 known that the tide would not prevent the motor-boat 

 " Eedwing " from maintaining her position on the marks during 

 the twenty to thirty minutes that the experiment occupied. 

 Two localities were used, the one just at the mouth of Port 

 Erin Bay with a depth of 8 fathoms, and the other a good 

 deal further out with a depth of 20 fathoms. The boat was 

 kept approximately stationary in the water, the hauls taken 

 as plumb as possible, and the rate of hauling up was fairly 

 constant at two minutes to 20 fathoms. The catches were 

 emptied from the brass bucket of the net direct into bottles 

 of 5 per cent, formaline, in which they remained until examined 



