THE CABLE SHIP ON REPAIRS. 185 



in the figure, is very useful when traffic has to be worked at 

 the cable-house when cable is put temporarily through by the 

 ship or if land-lines are down. On such occasions three men 

 can do the work, as only one is on at a time. No writer is 

 required, the operator reading and writing the words himself 

 as they come out, thus avoiding sound errors. 



The mirror instrument is provided with a short-circuit 

 piece, P, which is plugged in when sending. This is a better 

 arrangement than a two-way switch for sending and receiving, 

 because the mirror can be proved occasionally with the sending 

 key. 



A reversing switch, R, for reversing the signals received on 

 the mirror, is very convenient. If the signals from the ship 

 are reversed, all that has to be done is to turn the switch the 

 other way. The connections are marked on the diagram, and 

 will be easily understood. Another way of reversing the signals 

 is to twist the tube round in which the mirror is suspended, so 

 reversing the position of the poles of the magnet on the mirror ; 

 but this is not always a speedy way of working, as the controlling 

 magnet and lens may want re-adjusting, Another way is to 

 reverse the wires connected to the mirror instrument ; but with 

 a little practice reversed signals can be read with perfect ease? 

 necessitating no change whatever. 



In the ship's signalling connections there is generally fitted 

 a battery comm-utator for changing the number of cells rapidly, 

 to suit any length or condition of cable ; but, in order to avoid 

 delay, it is advisable to connect a shunt resistance to the mirror 

 instrument, which can be rapidly adjusted to make the signals 

 a readable size directly the ship is observed to be calling. The 

 wire connecting the shunt resistance to the mirror should be 

 disconnected before the ship calls, so that the instrument is in 

 its most sensitive state. The Silvertown Company employ a 

 water resistance device for adjusting the current passing through 

 the mirror instrument. 



Although now entirely supplanted on important lines by the 

 siphon recorder, the mirror instrument as devised by Lord 

 Kelvin is still largely in use. Every station has its speaking 

 mirror to fall back upon in case of one or more of the recorders 

 failing, and its mirror for cable-house use ; while on board ship 

 it is invariably ready as a stand-by in case of failure of the ink 



