.S/A' WILLIAM SI I-.. Ml: 'A'-S, 1>\R.S. 1 05 



arising from tin- amount of licat which it is necessary to employ 

 during tin- manufacturing process. 



On the other hand, notwithstanding the comparatively high 

 insnlaiini: property of india rubber, its low inductive capacity, and 

 its power to resist heat, its gradual dissolution in sea water is a 

 circumstance which alone renders it inadmissible as an insulator of 

 submarine telegraph wires, unless it is securely enclosed in another 

 waterproof medium, Gutta percha appears in eveiy respect well 

 suited for such an outer covering, being itself sufficiently insulating 

 to improve by its presence the insulation, and still more the loss 

 by induction of the covered wire ; applying itself closely to the 

 india. rubber ; being susceptible of forming secure joints; and 

 of resisting the sea water perfectly. 



The mechanical problem of forming a sound india rubber and 

 gutta percha covered wire, presented considerable difficulty. It 

 appeared to the author desirable that the india rubber should be 

 brought upon the wire without the application of heat, or solvents, 

 both of which often entail a gradual decomposition of that material,, 

 particularly when it i> exposed to atmospheric influence, in contact 

 with copper, or other metallic surfaces. Dr. Miller, in his Report 

 to the Joint Committee on the Construction of Submarine Tele- 

 graph Cables,* states that the liquefaction of india rubber is the 

 result of a process of oxidation ; from which it may be inferred 

 that the effect cannot take place where oxygen is entirely excluded. 

 I r was important, moreover, that the india rubber covered wire 

 should be perfectly cylindrical, or it could not be covered properly 

 with gutta percha in the die. Taking advantage of a peculiar pro- 

 j>erty of iiidia rubber cohering perfectly where two fresh cut sur- 

 faces are brought together, under considerable pressure, the author 

 lias constructed a machine, by which any number of coverings of 

 india rubber can be applied, in joining strips with longitudinal 

 joints, tightly upon the wire, care being taken that the joints of 

 consecutive coatings are at right angles to each other. 



Wires, and strands of wires, so covered with india rubber and 

 gutta percha, with and without intermediate layers of Chatterton's 

 compound, have been under trial under various circumstances, 

 exposed to the atmosphere, to water, or the moisture of the ground, 

 for nearly two years, without betraying any signs of gradual 



* Vide Appendix No. 4 to the above Report. 



