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LXIV. On Electric Conduction, and the possibility of curing the 

 retardation of Electric Waves in Submarine Telegraph Lines. 

 By John James Waterston, Esq.* 



IN the September Number of the Philosophical Magazine I 

 endeavoured to show that the thermal action in the metallic 

 part of the voltaic circuit took place on the surface only, and not 

 through the substance of the conductor. I took for granted 

 that there was no question as to this being the case in the con- 

 duction of common electricity, since all are agreed that, as charge, 

 it exists only on the external surface of conducting-matter. 



It appears I have been too hasty in assuming this to be an 

 established point. In the evidence before the committee on the 

 Atlantic cable, an experienced electrician holds that common 

 electricity is conducted through the substance of the wire, the 

 same as galvanic (Report, Appendix II. p. 327, § 208) ; and this 

 is more distinctly affirmed in a class-book on chemical physics, 

 which there is little doubt represents what is generally held and 

 taught by professors. 



At p. 459, § 276, of Dr. Miller's ( Chemical Physics/ the 

 process of conduction is described in the following words : — " In 

 all cases where electricity is in motion, whether it be exerted by 

 chemical action as in the voltaic pile, or by friction as in the 

 common electrical machine, the force is conveyed by the entire 

 thickness of the conductor ; the charge is not confined to the sur- 

 face, as occurs when the power is stationary, and produces effects 

 by induction only."" This is a distinct statement • but the evi- 

 dence upon which so important a point may be supposed to rest 

 is not given, nor is any reference made to where it may be 

 found. A little further on (p. 461) a figure is given of the ap- 

 paratus used by M. E. Becquerel in measuring the conducting- 

 power of wires of different metals for voltaic electricity. If by 

 means of such an apparatus we find that an iron wire plated with 

 copper conducts the same as a copper wire of the same diameter, 

 and that a copper wire plated with tin conducts no better than a tin 

 wire of the same diameter, we may at once conclude by such cru- 

 cial experiment that voltaic electric conduction is a surface phe- 

 nomenon ; and e. g. in designing a submarine telegraph-cable 

 with its strength in the core, we may be convinced of the pro- 

 priety of rather having a steel wire coated with copper than, as 

 in Allan's system, a copper central wire with steel wires enclo- 

 sing it. 



That common electric conduction is a surface phenomenon 

 may, I think, be held to be a direct consequence of its existing 



* Communicated by the Author. 



