38 THE SCIENTIFIC PAPERS OF 



that for long lines of telegraphic communication a better insulator 

 than gutta-percha could be found, which combined a great degree 

 of insulation with plasticity, toughness, and strength to resist the 

 ordinary accidents to which telegraphs were subjected. It had 

 been remarked by Professor Faraday that various specimens of 

 gutta-percha differed in conducting power, as also in durability. 

 Doubtless very considerable steps in the improvement of the elec- 

 tric telegraph would be effected if they could with certainty 

 produce gutta-percha of a quality giving it a greater power of 

 insulation. Another important point was what was the best form 

 of power to be used for the transmission of the electric current. 

 That must necessarily differ according to the uses to which the 

 instruments were put. A different power was required for short 

 distances to that which would be suitable for long distances, such 

 as the Atlantic telegraph. One advantage of magneto-electric 

 power, as opposed to that of the battery, was that the apparatus 

 was always ready and only required small mechanical power to 

 work it. It has been found to answer well for short distances, 

 and, with regard to its applicability to long lines, no doubt some 

 opinions would be given that evening. There had of late been 

 many improvements in the means of inducing electricity of high 

 power ; for instance, the Ruhmkorff coil, by means of which a 

 great increase in the power of the current had been produced ; 

 and thus immense intensity was obtained with a comparatively 

 small battery. It was stated that in order to obtain sufficient 

 intensity to work a length of telegraph such as the Atlantic cable, 

 they would require 500 Daniell's cells, whilst with the Kuhmkorff 

 coil it was probable they would be able to obtain sufficient inten- 

 sity with a much smaller number. Another important point was 

 the occasional rupture of the copper wire in submarine cables. 

 It was argued that by having the outer iron sheathing of a twisted 

 or spiral form, whilst the wires of the inner core were straight, 

 there was a greater power of stretching in the outer than in the 

 inner wires, and he did not know how far the breakages that had 

 taken place were due to that circumstance. He thought, how- 

 ever, it was very desirable to have the whole cable so constructed 

 that the stretching of the wires, if any, should be uniform, and 

 that one part of the cable should not stretch in a greater degree 

 than the other. 



