intended to reduce the effects of Inductive Action. 843 



still more marked; for, although considerable thermometric effects 

 were produced by the two plates of glass enclosed between the 

 tinfoil coatings, yet no appreciable effect could be obtained with 

 the same charge when porous layers were inserted between them. 

 Reasoning upon these results, it occurred to me that, in addi- 

 tion to the advantages before alluded to, to be derived from 

 increasing the thickness of the dielectric and the capacity of the 

 conductor, still further benefit would result by adopting some 

 modification of the foregoing arrangements in relation to the 

 cable. The interposition of porous or fibrous media between 

 the coatings and the jar or glass plate, reduces the effects of the 

 discharge ; and since it is the discharge, more than the charge, 

 which produces the embai-rassment of signals, it appears a fair 

 deduction that any arrangement which will reduce the effect of 

 this discharge, will to the same extent diminish the amount of 

 mischievous influence. 



Four modes of carrying out the conditions of the foregoing 

 experiments with regard to the cable, presented themselves. 



1st. By inserting a porous layer between the dielectric and 

 its inner coating (the wire), which could be done by covering the 

 wire with cotton, silk, or worsted, or any fibrous substance, pre- 

 viously to coating with gutta percha. 



2nd. By putting a fibrous coating of this kind over the gutta- 

 percha covering of a wire already insulated in the ordinary way, 

 taking care, of course, to make this coating impervious to 

 moisture. 



3rd. By inserting the porous or fibrous media between the 

 layers of gutta percha ; or 



4th. By adopting two or more of these processes in conjunc- 

 tion with each other. 



With regard to the first process, I found from actual experi- 

 ment that when the conducting wire was very small, as, for 

 instance, in the Atlantic Cable, the application of a porous cover- 

 ing to it previously to the gutta-percha coating unduly increased 

 its bulk in proportion to its original size, and thereby propor- 

 tionally increased the inner charging surface of the gutta percha. 

 But even under the most unfavourable circumstances, when for 

 the sake of experiment a double coating of fibrous material had 

 been put on, and the inner surface of the gutta-percha increased 

 to nearly three times its original dimensions, whilst the thickness 

 of the gutta-percha coating itself was less, thereby enabling it to 

 take up more than double the amount of static charge, yet the 

 effects of the discharge were no more than from the original 

 surface in contact with the wire; so that if only the same amount 

 of charge had been thrown in, less than half the original effect 

 might have been expected. 



