74 THE SCIENTIFIC PAPERS Of 



copper by degrees into a serpentine curve. These difficulties had 

 at present caused failures to a greater or less extent in all sub- 

 marine cables constructed with gutta-percha. But in the process 

 now described it was expected that the chances of failure through 

 defects of manufacture would be much diminished, as there was 

 less liability to accidental imperfections in the work, and the 

 durability of the cable was not affected by the temperature to 

 which it was exposed. 



The Chairman asked what would be the difference in cost per 

 mile between the new cable and one covered with gutta-percha. 



Mr. Siemens replied that for equal efficiency, or the same speed 

 of speaking, the new cable would be the cheapest, because a 

 thinner coating of india-rubber would be sufficient to produce an 

 equal insulating effect ; but if estimated by weight, a gutta-percha 

 cable would be the cheapest on account of the greater cost of 

 india-rubber. The first cost of the cable was, however, a secon- 

 dary question, the great object being to obtain a cable that 

 could be depended upon for a number of years. In a gutta-percha 

 cable, if the covering were thin at any one place, then each suc- 

 cessive current passing along the wire produced an alteration, 

 since the gutta-percha conducted at the leak by decomposition of 

 the water contained in its substance ; and this action gradually 

 disintegrated its substance and destroyed its insulating power at 

 that part, so that the electric current soon made its escape there. 



The Chairman asked how long the new cable would last at 

 work. 



Mr. Siemens replied that there was not one of the new cables 

 laid at present, and it required that several hundred miles should 

 have been down for some years in order to show practically its 

 durability in work ; but some miles had been made and tested 

 with very satisfactory results, and there was good reason for 

 expecting this construction of cable would prove far more durable 

 than those hitherto laid. 



