THE CABLE SHIP ON REPAIRS. 



189 



and the size of signals can by this means be regulated or the 

 signals reversed. 



When both coils are used the sensibility is considerably in- 

 creased, and the instrument in this state is of great use when 

 speaking through a faulty portion of cable, when the signals in 

 the ordinary course are weak and it is not desirable to increase 

 the battery power. On the other hand, by the use of the 

 auxiliary coil alone the instrument is rendered very dead-beat. 

 This device has been found of great service on board 

 ship. A glass window is shown in the illustration for 

 increasing the dead-beatness by air damping, but this 

 is not necessary in the ordinary use of the instrument. 



Fig. 97. 



Water damping has also been used from time to time with 

 considerable success. Fig. 97 shows the usual form of closed 

 tube and interior. 



To a light brass frame, with a disc, D, rigidly fixed at one 

 end. is fixed a spring, S, and a sliding piece, P. The lower end 

 of the silk suspension is attached to the end of the spring, and 

 its upper end is passed over a projection on the disc and 

 attached to the pin A. This pin has a screw-threaded shank, 

 which passes through a clear hole in the sliding piece P, and its 

 position can be regulated by a nut on the shank of the pin 

 without twisting the silk. This provides one means of adjust- 

 ment, while the sliding piece P can be shifted so as to regulate 

 the tension on the silk to any required extent, and is iinally 

 fastened in position by the set screw. The spring engages in a 



