SCIENCE AND PRACTICE. 349 



ing 40l)lbs per knot. The diameter of each wire is 0,048" ; 

 that of the strand, 0,146" ; and that of the gutta-percha, 

 0,464". The core was manufactured in knot lengths, and 

 tested, before it left the factory, under a pressure of 600 Ibs. 

 per square inch at a temperature of 75 Fahrenheit. A,t 

 Greenwich, the core was served with hemp, saturated with 

 salt water. The outer covering of 

 the deep-sea portion is formed by ten 

 wires (No. 13, B.W.Gr.) drawn from 

 Webster and Horsfall's homogeneous 

 iron, each surrounded by five yarns 

 of Manilla yarn, laid on spirally 

 with a preservative compound. A 

 section of this portion is shown in Fig. 162. 



Fig. 162. Its total diameter is M27. The shore end 

 portion, a length of 50 miles, of the deep-sea cable is served 

 with an extra thickness of hemp, around which is an outer 

 protection of wire strands. The weight of the deep-sea 

 cable, per knot, in air, is thirty-six hundred- weights, and its 

 breaking strain eight tons. 



The finished cable was subjected to careful tests of its 

 electrical conditions under the superintendence of the elec- 

 trician to the contractors. As the cable left the closing 

 machines it was coiled into tanks of water, and, when the 

 lengths became sufficiently great, was transported to the 

 steam- ship Great Eastern, which was destined to pay it out 

 across the Atlantic. 



The electrical conditions of the cables are unexceptionable, 

 and the complete manner in which every stage of the manu- 

 facture was carried out entitles the hope that, as they have 

 reached the bottom in safety, these lines will last an inde- 

 finitely long time in thoroughly good condition. The 

 employment of so large a vessel as the Great Eastern for 

 cable laying was a courageous experiment, and the result 

 is the most brilliant success of the present century. 



At the present moment there are upwards of 10,000 miles 

 of insulated wire submerged in the form of submarine cables, 

 in daily work, transmitting intelligence across different seas ; 



