346 THE ELECTRIC TELEGRAPH. 



This conductor was made by placing the four segmental 

 pieces in a tube and drawing the whole down as a solid wire. 

 The diameter of the wire so drawn is 0,111 inch ; its weight 

 225 Ibs. per knot. The conductor is insulated with four 

 coatings of gutta-percha and compound to the thickness of 

 0,380 inches, weighing 275 Ibs. per knot. The core was 

 served with the best Russian hemp, saturated in salt water. 

 The outer covering consists of twelve No. 7, B.W.G., galva- 

 nised iron wires, covered with two coatings of hemp and a 

 bituminous compound consisting of 34 parts of mineral pitch, 

 56 of silica, and 10 of tar. The cable was covered with this 

 mixture by means of an elevator driven by the closing 

 machine, so arranged that whenever the machine stopped 

 the elevator was also stopped, and no compound was poured 

 over the cable until the machine started again. In this way 

 the core was guarded against exposure to heat for any length 

 of time at one spot. 



The total length of cable laid down is a little over 1,150 

 knots in the following four sections : Kurrachee to G wader, 

 246 knots ; Gwader to Mussendom, 357'3 knots ; Mussen- 

 dom to Bushire, 392'7 knots ; and Bushire to Fao, 154-2 

 knots. 



The electrical conditions of the cable are good : its insula- 

 tion resistance, at 75 Fahr., being about three times as 

 great as the standard contracted for by the Gutta-percha 

 Company. 



71. Of more recent date still is the little cable laid in 

 1864, between Carthagena and Oran, by Messrs. Siemens ; 

 in point of length comparatively insignificant ; but em- 

 bracing a totally novel construction, and many points which 

 entitle it to a place here. 



The core was manufactured by the Gutta-percha Com- 

 pany, and did them infinite credit for excellent workmanship 

 and materials. It consisted of a strand of three copper 

 wires, weighing 72 Ibs. per knot, covered with three coats of 

 gutta-percha, alternated with as many coats of compound, 

 weighing 144 Ibs. per knot. Each separate knot was tested, 

 at a temperature of 24 C., under a pressure of 300 atmo- 



