82 THE SCIENTIFIC PAPERS OF 



cause. If the Rangoon cable, while in its heated condition, had 

 been tested on board the Queen Victoria, with the most accurate 

 galvanometer, it would have been pronounced more perfect than 

 any other cable hitherto sent out, because the Red Sea cable gave, 

 at ordinary temperatures, only 22 millions of units, and the Atlantic 

 cable, when reduced to the same sectional area, only 7 or 8 millions 

 of units ; whereas the Rangoon cable did not fall below 61 millions. 

 Yet if the heating had been allowed to continue only a few days 

 longer, it was absolutely certain that the gutta-percha would have 

 been softened, and the copper conductor would have sunk in the 

 insulating medium. 



A great desire was generally manifested for some improvement 

 upon the present construction of cables ; and he believed there 

 was great room for amelioration. An iron cable, without an 

 external covering to protect it against the action of the water, 

 should never be adopted. So far from the iron being an element 

 of strength, it became an element of actual weakness, when the 

 cable required to be raised for repairs. It had frequently been 

 observed, that the iron was oxidized, and in certain parts, rapidly 

 destroyed ; and if the ground was uneven, the cable would even 

 then break by its own weight, between the points of support. 

 But the outer covering should not be of hemp, for there had been 

 cases of hemp-covered cables having been completely -destroyed by 

 marine animals. As to the cause of the generation of heat in the 

 Rangoon cable, his own impression had been, that it was due to 

 the fermentation of the hemp covering ; he was bound, however, 

 to add, that, in Professor Miller's opinion, it arose simply from 

 the rusting of the iron. His own view was founded upon his- 

 observations that the resistance thermometers between the coils in 

 contact with the iron, exhibited a less temperature than would 

 follow from the resistance of the copper of the cable itself ; show- 

 ing that the core of the cable was 5 hotter than the spaces 

 between the iron covering. It might be, that both causes had 

 been active in producing the rapid increase of heat which had 

 been observed. 



The most important part, perhaps, of the cable was the insu- 

 lating medium, for which many new substances^had been proposed, 

 each possessing some degree of merit. The great disadvantages 

 attending the use of gutta-percha were, that it was readily softened 



