!^8 Mr. J. N. Heardev on the Atlantic Cable. 



object of the present paper to examine a few of the pecuharities 

 of svibmarine cables iu general, and tbe Atlantic Cable in par- 

 ticular, together with the electrical appliances employed for the 

 latter, with a view of ascertaining, if possible, the suitability of 

 the means to the end, and thence drawing some practical con- 

 clusions, which it is hoped may serve for future guidance. 



In order to do this, we must take a brief view of the different 

 conditions and functions of atmospheric and subaqueous lines, 

 and the pha;nomena to which they give rise. 



With a freely-insulated atmospheric wire, that is to say, with 

 a wire suspended in the air by insulating supports, after the 

 manner of our ordinary telegraph wires, the study of the pha^- 

 nomena developed in working through it is comparatively 

 simple, and the laws easily deducible. They resolve themselves 

 principally into the relation between the electro-motive force 

 of the battery, and the resistance of the wire through which 

 the current has to pass. I use the term resistance because it 

 is a more significant term than the converse one of conducting 

 power. It M'as formerly the custom to designate metals con- 

 ductors of electricity ; and so they are to a certain extent, but 

 they are all relatively so, and the best conducting of them afford 

 a certain amount of resistance. By the use of suitable instru- 

 ments the relative degrees of conducting power of the various 

 metals, or of different samples of the same metals, or, in other 

 w'ords, their relative resistances to the force of the electric cur- 

 rent, can be accurately determined. 



The Society wiU remember that in the year 1843 I exhibited 

 a magnetometer, which I had invented for determining the 

 relation between the electro-motive force of different voltaic 

 arrangements, and the resistance of conducting wires under 

 various conditions, as well as the influence which these modifi- 

 cations exerted over the development of magnetism in iron. 

 Por this invention I was honoured, in 1844, with the prize silver 

 medal of the Royal Cornwall Polytechnic Society. The engra- 

 ving and description of the instrument will be found in the 

 report of that Society for 1844. In April 1845, I exhibited the 

 instrument at the London Institution ; and an account of it was 

 given in the 'Electrical Magazine,' vol. ii. p. 133. More 

 recently an engraving and description of it have appeared in 

 Dr. Noad's Manual of Electricity. 



The instrument is now before the Society ; and I have intro- 

 duced it this evening because great stress has been of late laid 

 upon the valuable results arrived at by the employment of a 

 magnetometer, to the invention of which Mr. Whitehouse, the 

 electrician of tbe Atlantic Company, has laid claim, and with 

 which, to use his own expression, he weighs the strength of the 



