70 THE ATLANTIC. (CHAP. L 
beneath, with the beam above them. A second bag, or “ pock- 
et,” open at the bottom, hangs in the outer net, reaching about 
three-fourths of its length, and acts as a valve, preventing the 
washing out of its contents; and about a yard of the narrow 
extremity of the net is lined with “ bread-bag,” to give a chance 
of bringing up small things and a small sample of the bottom. 
The trawl is suspended by a bridle of rope, which is made fast 
to the runner at each end of the beam, and then continued down 
on each side and fastened to the end of the trawl-bag. The 
trawl is usually sent down with the additional weight of three 
14-lb. hand-leads, and, as in the case of the dredge, weights to 
about a hundred-weight and a half are slipped to a “toggle” 
400 to 500 fathoms before it on the line. 
The tow-net has been constantly worked during the cruise ; 
and Mr. Murray, who has taken charge of this department, has 
latterly got most remarkable results from using the tow-net just 
as we use a dredge, pulled along by the drift of the ship with a 
weight a few fathoms in advance, at different depths, down to 
100 fathoms. Mr. Murray finds that frequently, when scarcely 
any thing is to be found on the surface, all the pelagic animals 
which congregate there under favorable circumstances are to be 
met with at different depths below; and on more than one oc- 
easion he has taken animal forms with the deep tow-net which 
he has never seen on the surface. The tow-net used is of the 
ordinary form: a stout iron ring, a foot or eighteen inches in 
diameter, and a conical bag, three to four feet deep, of muslin, 
of bunting, or sometimes of “ bread-bag.” 
The Challenger is provided with a steam-pinnace, which is an 
invaluable adjunct for dredging and sounding in shallow water 
and ina smooth sea. She is a life-boat 36 feet in length, with 
two pairs of engines, one pair for propelling her, and another 
for heaving in the dredge-line. The propelling engines are a 
pair of high-pressure, direct-acting, vertical engines of six horse- 
power (nominal), with a horizontal tubular boiler, and a discon- 
