CHAP. VI. | DEEP-SEA DREDGING. OZ 
or two occasions, when an enormous load, once 
nearly a ton, came up in the dredge-bag, it de- 
livered the rope steadily, at a uniform rate of more 
than a foot per second, for the whole summer. 
A. powerful derrick projected over the port bow. 
A large block was suspended at the end of the 
derrick by a rope which, as in the case of the sound- 
ing-lne, was not directly attached to the spar but 
passed through an eye, and was attached to a ‘ bitt’ 
on deck. On a bight of this rope was lashed a 
powerful accumulator, the machine already described 
(p. 222), as of so much use in the management of 
the sounding-line. In dredging from a large vessel 
the ‘accumulator’ is invaluable. From the great 
strength of the springs the dredge is usually drawn 
along without stretching them to any great degree ; 
they become tense and taut, and yield, with a kind 
of slight pulsation, to the rise and fall of the vessel. 
Whenever they run out it is a sure indication that 
either the dredge has caught or the weight in it is 
becoming too great, and that the dredge-rope ought 
to be relieved by a turn of the paddle-wheel or screw. 
Care should be taken not to have the bight of the 
rope to which the accumulator is attached more 
than about twice the length of the unstretched 
springs. Springs in good order ought to stretch to 
much more than double their length ; but it is unsafe 
to try them too far, as a lash from one, if it were to 
give way, would be most serious. When a great 
strain comes upon the rope, it acts first upon the 
accumulator, pulling down the block and stretching 
the elastic bands; and a graduated scale on the 
derrick, against which the accumulator plays, gives 
