TO4 



THE SCIENTIFIC PAPERS OF 



TABLE II. 



SPECIFIC INDUCTION OF GUTTA PERCHA AND INDIA KUBBER. ALONE 

 AND COMBINED. 



lu the above Table, columns 1 to 5 inclusive give the description 



of the cable tested ; R is the outer radius and rthe inner radius of the 



p 

 insulating covering ; expresses the ratio ; column G, the tension, 



r 



column 7, the deflection observed ; and column 8, the specific 

 induction. It will be observed that the fall of insulation, with 

 the increase of temperature, is the more apparent and rapid, 

 the greater the proportion of gutta percha in the combination. 

 Thus, the specific resistance of the special gutta percha decreases 

 from 9-11 at 50 Fahr. to 1-50 at 80 Fahr., or to about one- 

 sixth of its original Value ; while the combination of two coat- 

 ings of india rubber and only one of gutta percha (No. 5), has, 

 under the same circumstances, only gone down to about one-third 

 of its insulation at 50 Fahr. On pure india rubber (No. 6) the 

 effect of temperature is still less. It was also found, that the 

 inductive capacity of the combined india rubber and gutta percha 

 wire is not greater than that of pure india rubber covered wire, that 

 of gutta percha being equal to 1, that of the combination being 

 about 0'7. It may further be remarked, that vulcanized india 

 rubber, although some of its qualities are in favour of its applica- 

 tion as an insulator for submarine cables, still cannot be recom- 

 mended as being well suited for that purpose, both from its tendency 

 to injure the conductor, by giving off a portion of its sulphur, and 

 converting its surface into a sulphuret, and also from the danger 



