380 SUBMABINE CABLE LAYING AND REPAIKING. 



rected by beading the lead wire or wires on the coil frame in a 

 direction to counterbalance the difference in weight. The 

 cradle board is made 4ft. long by 1ft. wide, of lin. board, with 

 a pair of guides Sin. long at one end to hold the scale base 

 steady ; the galvanometer being heavy needs no similar pro- 

 vision. Under the board two longitudinal stiffening pieces lin. 

 thick are fixed to prevent any yielding when lifted or tilted. 



It is not only the perfect balance obtained in this instru- 

 ment against rolling of the ship which renders it of such value 

 on board, but also the length of time it retains the balance and 

 the great facility of re-balancing the moving coil should the 

 original balance from any cause be put out. It is mainly due 

 to the excellence of balance that the coil is so very little, if at 

 all, affected by the vibration of moving machinery. Where 

 the vibration of the propeller, picking-up gear, or other ship's 

 machinery is so excessive as to affect the stability, this can be 

 overcome by placing a thick felt pad under the base of the 

 instrument. 



Universal Shunt. — This mode of shunting, devised by Messrs. 

 W. E. Ayrton, F.E.S., and T. Mather, was described by them 

 in a Paper before the Institution of Electrical Eogineers, in 

 March, 1894, entitled, "A Universal Shunt Box for Galvano- 

 meters." The galvanometer is permanently shunted by a high 

 resistance, which reduces its maximum sensitiveness slightly, 

 but not so as to be any disadvantage in the usual cable tests. 

 On the other hand, there is the advantage of constant damp- 

 ing on the galvanometer. With ordinary shunts the damping 

 is altered every time the shunt is adjusted, while the universal 

 shunt provides a path of fixed resistance for the induced cur- 

 rents, so that the galvanometer is always damped to the same 

 degree whatever its condition of sensitiveness. 



The universal shunt box in its original form had fixed sub- 

 divisions, giving multiplying powers of 10, 100, and 1,000, 

 which could be plugged in as required. In its present form the 

 high resistance permanently across the galvanometer is generally 

 divided Into a number of parts, over whioh a contact arm or 

 slider may be moved to vary the amount of shunt, as in Fig. 

 225. In position 3 where the slider ia at the extreme right 

 (marked 10,000), the galvanometer is in its most sensitive 



