64 THE ATLANTIC. [ CHAP. I. 
rectly fastened to the ring at the end of the arms, but is made 
fast to one of the end-bars of the dredge-frame, and is stopped 
to the ring by a single strand of bolt-rope. If the dredge get 
caught on a rock—a rare occurrence fortunately in deep water 
—the stop carries away, the direction of the strain on the dredge 
is altered, and it probably relieves itself and comes up end up- 
ward. In deep water, a 28-lb. deep-sea lead is usually hung from 
the centre of the tangle-bar, with four tangles on each side. 
It is altogether a new experiment to dredge and to take 
deep-sea observations from so large a ship, and it seems to pre- 
sent some special difficulties, or, at all events, to require great 
management. The weight of the ship is so great that there 
can be no “give and take” between her and the dredge, such 
as we have in smaller vessels. If there be any way on, the im- 
pulse to the dredge is irresistible, and it seems to tend to jerk 
it off the ground. The roll of the ship, her height above the 
water, her want of flexibility of movement compared with the 
vessels which had been previously employed for the purpose, 
raised new questions as to the method of working. 
Dredging and sounding are carried on in the Challenger 
from the main yard-arm. A strong pendant is attached by a 
hook to the cap of the mainmast, and by a tackle to the yard- 
arm (Fig. 17). A compound arrangement of fifty-five to sev- 
enty of Hodge’s patent accumulators is hung to the pendant, 
and beneath it a block, through which the dredge-rope passes. 
The donkey-engines for hoisting the dredging and sounding 
gear are placed at the foot of the mainmast on the port side. 
They consist of a pair of direct-acting, high-pressure, horizontal 
engines, collectively of eighteen horse-power nominal. Instead 
of a connecting-rod to each, a guide is fixed to the end of the 
piston -rod, with a brass block working up and down the slot 
of the guide. The crank-axles run through the centre of the 
blocks, and the movable block, obtaining a backward and for- 
ward motion from the piston-rod, acts on the crank as a con- 
