CHAP, vi.] DEEP-SEA DREDGING. 



247 



or two occasions when an enormous load, once 

 nearly a ton, came up in the dredge-Lag, 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-line, 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. Prom 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 unst retched 

 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 Avere 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 der 

 rick, against which the accumulator plays, gives in 



