400 THE ELECTRIC TELEGRAPH. 



then the point of the disc (which makes one revolution 

 per hour) gets beyond the contact-spring,, and the disc turns 

 without meeting with another contact for twenty-four 

 minutes, during which time, therefore, the cable end is in- 

 sulated and the ship measures the dielectric resistance. At 

 twenty- eight minutes past a point of the disc touches a metal 

 spring connected directly with earth, and the ship is enabled 

 to measure copper resistance. This contact is also of only 

 four minutes' duration ; and then succeeds an insulation of 

 the cable end, as before, for another space of twenty-four 

 minutes, giving the ship, in all, forty-eight minutes in each 

 hour for insulation measurements. At fifty-six minutes past, 

 the disc or land end of the cable makes contact with a spring, 

 leading to the measuring-board at the station ; and, during 

 the succeeding four minutes, the operator there measures in- 

 sulation resistance, those on board taking care to insulate the 

 ship end in time to let the land-station make the necessary 

 observations, and, at the full hour, to put the end to the 

 Morse apparatus on board, that the land -station can com- 

 municate his result in the four minutes during which he is 

 allowed to speak. 



Very recently, Mr* Willoughty Smith, Electrician to the' 

 Gutta-percha "Works, suggested a method by which, during 

 the submersion of a cable, its insulation resistance could be 

 measured on board the ship, and simultaneously an indication 

 of insulation be given at the land end. In addition to this, 

 without entirely disturbing the continuance of these tests, 

 messages can be passed backwards and forwards. In the 

 event of a fault occurring in a cable, it is always of great 

 importance to be able to communicate the results of measure- 

 ments made on shore, where the instruments are steadier and 

 more delicate, *and of necessity the results more to be de- 

 pended upon, to the electrician on board the ship, who uses 

 the data for calculating the distance of the fault, in order 

 that he may judge what steps are expedient to be taken for 

 recovering it ; and such a communication may be delayed for 

 a considerable time, when every moment is precious, when 

 a system of clockwork such as that just described is us ad. 



