APPLIANCES FOR COLLECTING PELAGIC ORGANISMS. 
145 
“firing,” for wfien used at uiglit its track could fie distinctly seen several fatlioins 
fielow the surface. On one occasiou, when a school of mackerel was attacked with it 
on a dark night, we could see the mass separate only a few feet in advance and then 
liromptly close again in its rear, and not one was caught. The school was so dense 
that it seemed impossifile to drag so large a net among them without catching one or 
two at least; but after an hour or more of towing in every direction at varying speeds 
from 1 to 8 knots, without the capture of a single specimen, we were impressed with 
the fact that our latest invention was not a success for mackerel fishing. Slight con- 
solation was afforded us at the reflection that as a crab net it would fie immense. 
Surface tow nets attached to the dredge rope were used on board the Challenger 
for intermediate collecting, but a knowledge of the depths at which the specimens 
were secured was still lacking. The same jiractice was followed on board the Fish 
Haiclc until we improved upon it by adopting wing nets, which were attached to each 
end of the trawl beam, and performed the functions of collectors from surface to bot- 
tom, and thence to the surface again. They were like an ordinary tow net with a 
pocket added. The material Avas cheese cloth, and being much finer than any portion 
of the trawl which they accompanied, they usually contained a miscellaneous col- 
lection of small forms, many of which would not have been secured by any other 
method in practice at that time. Of course, we had little knowledge of the depths at 
which the various forms were secured. Such as were common to both wing net and 
surface net were, in a general way, assigned to areas within the influence of sunlight, 
while those found in the wing nets alone were allotted to depths more profound. 
sigsbee’s gravitating trap. 
Prof. Alexander Agassiz long felt the need of some reliable method of ascertaining 
the depth at Avhich specimens were taken, and in 1880 he requested Lieutenant Com- 
mander G. D. Sigsbee, U. S. Navy, to cooperate Avith him in devising the necessary 
apparatus. Referring to this matter, Sigsbee says (Bulletin of the Museum of Com- 
parative Zoology, Cambridge, vol. Vi, pp. 155-6) ; 
It occurred to me tliat by using an apj^aratus in connection with a line and lead, paid out verti- 
cally as in sounding, and by dragging vertically, instead of horizontally, as formerly, there would be 
as much certainty with regard to deiiths as in the old method, and that simple mechauical devices 
could be invented to satisfy the conditions of the work. *■ * * Oar plan is to trap tlie specimens 
by giving to a cylinder, covered with gauze at the upper end and having a Hat valve at the lower end, 
a rapid vertical descent between any two depths as may bo desired, the valve during such descent to 
keep open, but to remain closed during the process of lowering and hauling back with the rope. An 
idea of what it is intended to effect may be stated briedy thus ; Specimens are to be obtained between 
the intermediate depths A and B, the former being the np2>ermost. With the apparatus in position, 
there is at A the cylinder suspended from a friction clamp in such a way that the weight of the cylinder 
and its frame keeps the valve closed; at B, there is a friction buffer. 
Everything being ready, a small weight or messenger is sent down, which on striking the clamp 
disengages the latter and also the cylinder, when messenger, clamp, and cylinder descend by their own 
weight to B, with the valve open during the passage. When the cylinder frame strikes the buffer at 
B, the valve is therefore closed, and is kept closed thereafter by the weight of the messenger, clamp, 
aud cylinder. The friction buffer, which is 4 inches long, may be regulated on board to give as many 
feetof cushioning as desired. * * It is necessary tirst, to regulate the buffer, to cushion the stox>page 
of the falling weights, which are, cylinder aud frame, 33 pounds; clamp, 4 pounds; messenger, 8 
pounds; total, 50 pounds. The adopted a resistance of about 80 pounds (tliis resistance being, of 
course, constant during the whole movement of the buffer), it having been found that a blow of that 
F. C. B. 1894—10 
