222 THE DEPTHS OF THE SEA. [cHAP. Vv. 
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 with 
some degree 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 
important 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 lbs. The 
sounding-line was wound amidships just abaft the 
donkey-engine on a large strong reel, its revolution 
