CHAP. XVIII.] DEEP-SEA SOUNDINGS 393 



It being impracticable to regulate the speed of the engine by 

 hand according to the heave of the ship, in order to obviate 

 the sudden and excessive strains on the wire so caused, an 

 ingenious mechanical arrangement has been fitted to machines 

 of recent pattern, by which frictional discs, geared by cog- 

 wheels and capable of adjustment, are interposed on the axle 

 connecting the grooved wheel actuated by the hemp swifter 

 and the revolving drum carrjdng the wire. 



By this arrangement the latter can be controlled as desired, 

 both in speed and direction of motion, by means of a lever 

 regulating a strap on the frictional discs, which may be set 

 by experiment to act at any given tension of the wire. As the 

 tension approaches this limit, the velocity of revolution of the 

 drum is automatically checked ; and if the tension further 

 increases, the motion of the drum is actually reversed, thus 

 causing the wire to run out, until the tension is relieved 

 sufficiently to allow the frictional discs again to act in the 

 direction of heaving in. 



The drum may be stopped instantly by moving the lever in 

 the proper direction to throw the apparatus out of gear. 



The large machine is represented in Fig. 78, but further 

 detailed description will not be given, as the type may be further 

 altered. 



The wire used is galvanised steel wire of 20-gauge. It is wire, 

 supplied on drums in 5,000-fathom lengths, which are some- 

 times in one piece, but often have a splice in them. The 

 drums are in hermetically-sealed tins. Though galvanised, 

 the wire requires looking after. The galvanising process is 

 not perfect, and it may be thin in some places, and even actually 

 bare spots may occur. The wire should therefore be passed 

 through an oily rag as often as possible, and oily cloths kept on 

 the machine to protect the outer layers from damp air. After 

 a long sounding cruise it is probably safer to condemn the wire 

 on the machine. 



A fortnight's continuous use is about the limit to the trust- 

 worthiness of any kind of wire ; no amount of care wiU. prevent 

 it from becoming brittle ; and directly it can be snapped by 

 twisting in the hand, it should be condemned and passed on to 

 the boat's machines. A magnifying-glass will assist in ex- 

 amining its condition. 



