372 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
angle at which it is to be towed, enter Table II, Bowditch Navigator, and find the 
length of rope required to maintain the net at the proper depth and steam ahead 
slowly, veering gently until the predetermined scope and angle are attained. The 
latter can then be maintained with sufficient accuracy by frequent observations with 
the dredging quadrant and properly regulating the speed. 
A correction, to be subtracted from the figures taken from Table II, Bowditch, will 
be reijuired for the catenary curve, as the sinker and the net being afioat at an inter- 
mediate depth will sink more rapidly than the rope which is being dragged laterally 
from 150 to 200 feet per minute through the water. It is quite impossible to give 
an invariable rule for making this correction. It may be said, however, that the angle 
of 40° has usually been adhered to on board the Albatross, which involves a speed of 
2 knots per hour, ai)prosimately. Under these conditions a deduction of 8 fathoms 
per 100 fathoms in depth may be made up to 500 fathoms; 9 fathoms iier 100 between 
500 and 1,000 fathoms; and 10 fathoms per 100 between 1,000 and 2,000 fathoms. 
This approximate rule is applicable to the stated conditions only, but will serve as 
a general guide until the explorer learns from experience the corrections required by 
his own methods and apparatus. 
ILLUSTRATIVE EXAMPLE. 
Depth at which the net is to he towed 500 fathoms 
Angle of the tow rope 40° 
Length of rope required, Table II, Bowditch (550 fathoms 
Correction for catenary curve, 8 fathoms per 100 fathoms depth — 40 fathoms 
Length of tow rope required 610 fathoms 
To recover the net, having towed it a sufficient length of time, stop the engines 
and back slowly until the tow rope hangs vertically, reeling in sufficient rope to main- 
tain the net at a uniform depth; send the messenger down and release the weights by 
reversing the tumbler, when they will exert a sudden and sufficient force on the ends 
of the drawstring to securely close the lower jiart of the net. 
The messenger sinks at the rate of 100 to 110 fathoms per minute, and its impact 
can usually be felt by grasping the rope, but this method is not always reliable, hence 
it is advisable to use time intervals, allowing the safe limit of 100 fathoms per minute. 
Having closed the lower bag, steam slowly ahead and reel in at the rate of 25 to 
28 fathoms a minute until the net is on board. The upper iiortion from the mouth to 
the drawstring remaining open, will usually be found to contain an assortment of 
specimens collected on the way up. 
A few turns of a lashing should be taken around the net immediately below the 
drawstring as soon as possible after the apparatus reaches the deck and while it is 
hanging vertically by the tow rope, to avoid the possibility of opening communication 
with upper and lower compartments by the accidental slackening of the drawstring. 
This done, the frame should be lowered gently on deck, the lashing removed from 
the tail of the net and the parts turned back, leaving the inner or silk gauze lining 
exposed; remove its lashing, carefully open the bag over a iian of prepared sea water 
which has been carefully strained to remove any surface forms it might have contained, 
and finally rinse the net in it to remove minute specimens adhering to its sides or 
lodged in the numerous folds. 
The contents of the lower bag secured, the drawstring is removed, the upper bag 
turned inside out into a tub of water, and the specimens secured by thorough rinsing, 
after which the lashing is taken off and the net carefully washed, usually by towing 
