222 THE DEPTHS OF THE SEA. [CHAP. v. 



attached directly to the derrick, but to a rope which 

 passed through an eye at the end of the spar, and 

 was fixed to a ' bitt ' on the deck. On a bight of 

 this rope between the block and the ' bitt ' the accu- 

 mulator was lashed. This consists of thirty or forty 

 or more of Hodge's vulcanized india-rubber springs 

 fastened together at the two extremities, and kept 

 free from one another by being passed through 

 holes in two round wooden ends like the heads of 

 churn-staves. The loop of the rope is made long 

 enough to permit the accumulator to stretch to double 

 or treble its length, but it is arrested far within its 

 breaking point. The accumulator is valuable in the 

 first place as indicating roughly the amount of strain 

 upon the line ; and in order that it may do so witli 

 some decree of accuracy it is so arranged as to play 

 along the derrick, which is graduated from trial to the 

 number of cwts. of strain indicated by the greater or 

 less extension of the accumulator ; but its more im- 

 portant function is to take off the suddenness of the 

 strain on the line when the vessel is pitching. The 

 friction of one or two miles of cord in the water is so 

 great as to prevent its yielding freely to a sudden jerk 

 such as that given to the attached end when the 

 vessel rises to a sea, and the line is apt to snap. A 

 letting-go frame like that used on board the ' Hydra,' 

 a board with a slit through which the free end of the 

 sounding machine passed, and which supported the 

 weights while the instrument was being prepared, was 

 fitted under the stern derrick. The sounding instru- 

 ment was the ' Hydra,' weighted with 336 Ibs. The 

 sounding-line was wound amidships just abaft the 

 donkey-engine on a large strong reel, its revolution 



