-S7A' WILLIAM -SVA'.J/AA'.s, l-.R.S. 15 



ought to be of the best conducting material, such as copper. 

 The conductor constituted the weight to be carried, and should, 

 therefore, be as light as possible, consistent with the highest 

 conducting power ; and, to insure its continuity, it should be 

 relieved from strain by the external coating. He thought that 

 the newly-discovered metal, aluminium, might be used, with ad- 

 vantage, in deep-sea cables, as it was nearly equal in conducting 

 power, and was only one-third the weight of copper. If the pro- 

 posal to substitute an iron conductor should ever be adopted, it 

 would be found that the retardation by lateral induction, which 

 was the great impediment to the successful working of long sub- 

 marine communications, would be much increased, and would 

 eventually become practically insurmountable. After the con- 

 ductor was determined upon, there came the consideration of the 

 insulator, the thickness of which ought to be increased with the 

 length of the cable, in order to keep down the retardation by 

 lateral induction. The insulated conductor, if composed of copper 

 and gutta-percha, was always specifically heavier than water, and 

 it was the outer covering which must give strength to the fabric. 

 If the outer coating was of soft material, such as caoutchouc or 

 gutta-percha, there was no strength to resist the action of the 

 brake, and the coating would be torn away from the wire within 

 it. Therefore the outer coating should be of hard material, and 

 of great strength, so as to resist the longitudinal strains during 

 the process of submerging, but it should add as little as possible 

 to the weight. He thought that no material fulfilled these con- 

 ditions so well as soft steel. A thin steel wire covering would 

 produce a cable of the least weight, and capable of suspension in 

 the greatest depth. Nor would it be more expensive than the iron 

 coating, if power of suspension was taken as the basis of the 

 calculation. 



