844 Mr. J. N. Hearder on a New Form of Telegraph Cable. 



Since, however, according to the experiments with the glass 

 plates, the porous material was equally effective on the outside, 

 or between two plates, it would appear that the most eligible 

 situation for the fibrous layer in the cable, would be either 

 between the coatings of gutta percha or externally to them; and 

 I doubt not that in either of these situations it would act with 

 the cable, as with the glass plates, in materially reducing the 

 effects of the discharge. 



There are also other considerations of a mechanical character 

 which render these modifications of the arrangement preferable. 

 I venture then to recommend, with considerable confidence, the 

 adoption of this plan as a simple and efficient mode of greatly 

 reducing — I will not go so far as to say entirely obviating — 

 the embarrassing influences of the residual discharge. 



In a word, a cable constructed upon the principles here laid 

 down will possess the following electrical quahfieations, viz. — 



Its conductor will be of ample dimensions, thereby reducing 

 the tendency to produce static induction. 



The dielectric or insulating coating will also, by its increased 

 thickness, not only improve the insulation, but have a diminished 

 capacity for taking up inductive charge; and, lastly, the insertion 

 of the fibrous substance will go very far to obviate the mis- 

 chievous effect of any amount of charge that may be taken up, 

 since by analogous arrangements we find that from 80 to 90 per 

 cent, of this influence may be intercepted. 



I caunot close this paper without alluding to the mechanical 

 advantages also possessed by this form of cable. It is well known 

 that when the gutta-percha coating of a cable is subjected to 

 great strain, small fissures, before imperceptible, gradually 

 become apparent from the separation of surfaces between which 

 there was previously a want of perfect cohesion, although without 

 this strain the cohesion might have been sufficient for electrical 

 insulation, and the fissures might not have been formed. I have 

 no doubt that the Atlantic cable has suffered in this manner, ~ 

 since it had no provision for preventing the gutta percha from 

 stretching. 



Propositions have lately been made to form the core in such 

 a manner as to take all the strain; but independently of the most 

 serious electrical objections to a conductor compounded of iron 

 and copper, I venture to predict that whenever such a cable shall 

 be subjected to the strain of passing over pulleys, the gutta- 

 percha coating will separate into pieces and slide over its in- 

 cluded conductor. The interposition, however, of flax or hemp 

 strand, which is a very eligible material, and which may be either 

 braided on or laid on in a veiy long twist between the layers of 

 gutta percha and incorporated with them, will communicate such , 



