348 THE ELECTRIC TELEGRAPH. 



merged with success between Bona and Bizerta, and 

 worked very satisfactorily. 



At the date of the first Atlantic cable the mechanical 

 department was far ahead of the electrical. The cable was 

 successfully laid mechanically good, but electrically bad. 

 At the present day the electrical department has made great 

 progress towards perfection. A striking proof of this is that 

 cables now rarely or never breakdown through electrical faults. 

 To remedy the rapid oxidation of the iron- wires in sea-water, 

 experiments have been made, although on no very extended 

 scale, to tar the cable as it passed out of the ship. Subse- 

 quently Messrs. Bright and Clark patented their method of 

 covering the finished cable with a bituminous compound, 

 which should preserve the iron by excluding entirely the 

 sea-water. In the development of the same idea, Messrs. 

 Siemens have made a cable based on more scientific principles. 

 It consists in covering the iron wires with hemp, and the hemp 

 with zinc, in such a way as to form a large iron- zinc element. 

 Zinc is electro-positive in regard to iron, and is, therefore, 

 dissolved, while the iron, forming the negative element, is 

 left undisturbed. So long as the zinc lasts the iron must 

 remain intact ; but the zinc in oxidising forms upon itself an 

 insoluble crust, which preserves it for an indefinite time, so 

 that a cable so constructed must last for years. 



72. The most recent and unconditionally the most im- 

 portant cables at present are those which have been laid 

 over the route of the old Atlantic line. This great under- 

 taking comes at the right moment, in every respect, to 

 realisation, when both the electrical and mechanical depart- 

 ments have arrived at comparative perfection. 



The cable was manufactured by the Telegraph Construction 

 and Maintenance Company an incorporation of the firms of 

 Messrs. Glass, Elliott, and Co., of Greenwich, and the Gutta- 

 percha Company, of Wharf Road. The core was made by the 

 Wharf Road branch. It consists of seven No. 18 gauge 

 copper wires, twisted into a spiral, weighing 300 Ibs. per 

 knot, covered with four coats of gutta-percha, between which 

 are intervening thin layers of Chatterton's compound, weigh- 



