152 SUBMAEINE CABLE LAYING AND EEPAIKING. 



from Waterville to Canso (2,161 nauts), and in 1901 a fourth 

 for the same Company between the same stations via the 

 Azores. This vessel has therefore laid 24,017 nautical miles of 

 transatlantic cables. The other cables marked on the map 

 bring this total up to 26,220 nautical miles, these being laid 

 between St. Pierre and Louisburg, Brest and Cornwall, Water- 

 ville and Le Havre, and Waterville and Weston-super-Mare- 

 When at home the '* Faraday" lies in Millwall Docks. 



Tests during Laying. — While the ship is laying cable, con- 

 tinuous attention is given to electrical tests both on board and 

 on shore to prove the continuity of the conductor and the good 

 insulation of the dielectric. The requisite instruments for shore 

 are landed from the ship and set up in the cable-house while the 

 shore-end is being laid, so that all is in readiness as soon as the 

 ship splices on and lavs out to sea. For speaking to the ship, the 

 instruments required are condensers (of about 20 to 100 micro- 

 farads capacity to suit the varying lengths of cable in circuit), 

 signalling key, battery and mirror. For the tests two sensitive 

 galvanometers are required, also high resistance, discharge key, 

 condenser and commutator. A bridge with all connections ready 

 is prepared in case it is necessary to take a test by this means. 



The connections, as arranged in the cable-house and ship's 

 testing-room, are given diagrammatically in Fig. 74, which 

 is the arrangement devised by Mr. Willoughby Smith. The 

 shore does not put on any current for the tests during laying, 

 this coming only from the ship. While paying out, the 

 ship always has one lever of the testing key clamped down, 

 keeping current on the slides and cable, and reverses this at 

 pre-arranged intervals — generally at every hour. On shore the 

 cable is connected to the high resistance and galvanometer, 

 and also to the stop of discharge key, by plugging in the bottom 

 bar of the commutator. This plug is not removed unless the 

 ship signi6es that she wants to speak, when it is taken out and 

 put in the left-hand bar. If a bridge test is required, the plug 

 is put in the right-hand bar. 



The cable is then, during paying out, connected to earth on 

 shore through a very high resistance and sensitive galvano- 

 meter, allowing only an infinitesimally small current to pass, 

 but giving a convenient deflection of the spot of light on the 

 scale. The end of the cable is therefore practically insulated. 



