452 SCIENCE. [Vou. ILl., No. 62. 
the interior of the trawl, would have passed through 
the meshes of the net, were caught by the long threads 
of the tangles. hv it 
That the strain on the drag-line may be eased, a 
wire rope (P, fig. 9) is made fast to the end of the 
beam, and, after passing over a block, is connected 
with a spring balance or ‘accumulator,’ A, made of 
disks of rubber, and attached to the mast. Da 
The size of the trawl used depends upon the depth 
to be reached and upon the weather. As a general 
rule, it may be said that in good weather a trawl 
of three metres length is used to explore a depth of 
thirty-six hundred metres. Beyond this depth, a 
three-metre trawl] cannot be used. Lower than three 
thousand metres, the additional burden is a hundred 
and eighty-eight kilograms. 
When every thing is ready for the lowering of the. 
trawl, the machines are freed, and at first the net is 
allowed to fall by its own weight and that of the cable 4 
which holds it; but after a little time the rapidity 
becomes too great, and must be regulated by the : 
brakes. During the descent, the ship is «held with . 
the wind at the stern, or at least on the side, with 
its fore and mizen sail set. It must have a speed 
of at least two knots; and if with the wind alone 
it cannot make so much, its rate must be increased 
by steaming. Commandant Parfait discovered that 
this speed of two or three knots was absolutely 
necessary, if the cable were to be always taut. If 
this tension was not maintained, the cable descend- 
ed more quickly than the trawl, rolled itself up on 
the bottom, and the net dropped on the bundle thus 
formed. In this case the cable became tangled, and 
kinks were formed in great numbers throughout its 
length. A register on the windlass (fig. 6), around 
which the cable passes before running into the water, , 
indicates the moment when the net should reach the 
bottom. When this is reached, the full force of the 
brakes is applied, and the cable firmly held in place. 
To insure the drawing of the trawl] along the bot- 
tom, it is necessary to unroll a length of the cable 
greater than the depth of the sea. To a depth of 
six hundred metres, twice the length is paid out: 
deeper than this, five or six hundred metres more 
than sufficient to reach the bottom are run off. 
While the trawl is dragging, the ship is kept in such 
a position that it slowly drifts sideways. The time 
during which the trawl is left on the bottom varies 
greatly with the depth. In deep dredging it is 
dragged three-quarters of an hour, at times even sev- 
eral hours. When the trawl rises from the water, 
it is drawn upon the deck, and placed as seen in 
fig. 11. In order to obtain the animals enclosed in the 
thick, sticky mire often brought up in the trawl, 
the latter must be sifted very carefully. For this 
purpose a set of metallic frames, placed one upon 
the other, and raised on balls, is used. By simply 
giving these frames a backward and forward motion 
while water is showered into the mud, the smallest 
animals are obtained without receiving any injury. 
We have endeavored to show this operation in fig. 
i. 
Besides the sounding and dredging apparatus, 
’, 
9, 
‘ 
0 
© 
M\ 
\) 
XX 
() 
‘ 
WX 
‘V 
Mt 
i et 
9 
‘) 
7 
: 
" 
) 
Qn! 
\ 
ae 
ESSE S SOS 
SOS SOS SSS 
BS OCSSS SS SoS Ss 
Fre. 10.— The trawl. 
