Mr. J. N. Hearder on the Atlantic Cable. 33 



would be only one-sixteenth ; and this I believe is very much 

 within the mark, for reasons which I have before stated. 



In applying these principles as a test in the examination of 

 the Atlantic Cable, its construction appears objectionable in many 

 respects. 



I do not here intend to discuss the merits of its mechanical 

 arrangement, such as the propriety or impropriety of coating it 

 externally with wire, or its suitabihty or otherwise for the pur- 

 pose of a deep-sea cable, though I consider that it is far from 

 being the best form that might have been adopted for the pur- 

 pose, since no provision is made to enable each element of which 

 the cable is composed to take its own due proportion of the strain 

 to which the whole might be subjected. I wish to confine my- 

 self more particularly to a consideration of its electrical qualities, 

 which, from the very first, I have unhesitatingly disapproved of, 

 not only pubhcly but privately in frequent friendly discussions 

 with Mr.Whitehouse, the electrician of the Company, with whom, 

 though I have the highest respect for his talents, I happen to 

 differ very widely upon some important fundamental points. 



I shall treat tbe subject in a dispassionate, scientific spirit, and 

 deduce my reasonings from established electrical laws, and not 

 from speculative theory. The first feature, then, which strikes 

 the electrician, is the smallness of the conductor. It is a well- 

 established electrical law, that the resistance which a wire ofi^ers 

 to the passage of the electric current is directly as its length, 

 and inversely as its transverse sectional area, or, in ether words, 

 inversely as its mass. A wire of double the mass, and the same 

 length as another, will conduct twice as well, it being equivalent 

 to two wires laid side by side. A wire of the same thickness, 

 but twice the length of another, will conduct only half as well; 

 therefore if doubling the length reduce the conducting power 

 one-half, it is only requisite to double the mass of the wire 

 which is twice as long, to bring it up to the original standard 

 of conducting power. By parity of reasoning, if a wire of 

 given mass, and 200 miles in length, and possessing a certain 

 amount of conducting power, have its length increased tenfold, 

 its mass must be increased tenfold also, in order to maintain the 

 same conducting power relatively to the electro-motive force of 

 the battery working through it. If, with the increased length, 

 its mass be only increased fivefold, then it will possess double 

 the resistance, and will require a battery-current of twice the 

 intensity to overcome it ; or if the length be increased ten times 

 without increasing the mass at all, then the battery power must 

 be increased ten times, or telegraphic instruments of ten times 

 the amount of susceptibility must be used. The wire of the 

 Atlantic Cable is composed of seven small wires, of No. 22 gauge, 

 Phil. May. S. 4. Vol. 17. No. 111. .hin. 18.59. D 



