SCIENCE AND PRACTICE. 347 



spheres, by Reid's method, and had at that temperature and 

 pressure an average resistance of insulation of over 600 

 millions per knot. 



The core was covered at the cable factory of Messrs. 

 Siemens Brothers, at Charlton, with a laminous sheating, 

 patented by Mr. C. W. Siemens. It was passed 

 through a series of three machines in close suc- 

 cession. In going through the hollow spindle of 

 the first machine, a close spiral covering of fine 

 hemp strings was applied in such a way that the 

 strain upon each of the strings was nearly equal. 

 This strain was adjusted by friction springs at 

 the sides of the bobbins containing the hemp. 

 The second machine, similar in construction to 

 the first, supplied a second covering of hemp, 

 wound in the opposite direction to the first. 

 Finally, the third machine covered the rope, 

 spirally, with four strips of sheet copper, under a 

 moderate pressure. By an ingeniously constructed 

 covering tool, these strips were made to overlap 

 each other nearly half their breadth, by which 

 the copper covering became about twice the thick- 

 ness of the sheet. Fig. 161 shows a perspective 

 view and section of a piece of this cable. 



The cable was laid completely from the Douane 

 at Ain-el-Turck, on the north coast of Africa, 

 to the harbour of Carthagena, on the south Fl &- 16L 

 coast of Spain, but broke about ten miles from the Spanish 

 coast, soon after its submersion. During the time it lasted 

 the resistance of its insulation was over a thousand millions 

 per knot, and the speed with which it could be worked quite 

 equal to that which the telegraphists had attained. The rup- 

 ture occurred over the sudden fall which runs east and west 

 along the Mediterranean, and on which the Toulon -Algiers 

 cable parted some years before. This experiment will pro- 

 bably be the last to lay down a cable over this dangerous 

 bottom. 



A cable of the same construction was subsequently sub- 



