32 THE SCIENTIFIC PAPERS OF 



of the sheathing, which is necessarily a retarding cause, and 

 is, moreover, productive of a disturbing extra current, may be 

 neutralised. 



In calculating the time required for an electric current to 

 traverse a cable of given length and proportion, it may be received 

 as an experimental datum to start from, that it reached the distance 

 of 1,000 miles in one second, in a cable consisting of No. 1 6 

 copper wire coated with gutta-percha to the thickness of fV^s of 

 its diameter, a proportion most generally adopted. The discharge 

 of the same cable would occupy practically about two seconds, and 

 these times go on increasing in the ratio of the square of the 

 length of the conductor, in as far as the retardation by electric 

 charge is concerned, and in the simple proportion of losses by 

 leakage, voltaic induction, and magnetisation, the result being a 

 mean between the two ratios. 



With these facts before us, it would have been impossible to 

 work an electric telegraph across the Atlantic or Indian oceans, 

 with anything approaching a commercial result, and the idea must 

 have been abandoned, but for Faraday's timely discovery that 

 several electric waves may co-exist, following each other in a long 

 cable, whereby the number of impulses to be transmitted in a given 

 time may be greatly increased. 



A difficulty experienced in carrying this method of working into 

 effect, is the partial merging of the separate waves into an almost 

 uniform electric charge of the conductor, which causes the receiving 

 instrument to be permanently affected. This difficulty, has, how- 

 ever, been removed by a return to Gauss and Weber's method of 

 working, in sending always two opposite currents in succession, 

 whereby not only the effective value of each wave is doubled, but 

 accumulation of electric charge is entirely prevented, because the 

 two opposite waves, in emerging, destroy each other. This method 

 of working would, however, not be complete without a return also 

 to the same description of current which Gauss and Weber 

 employed. It has, indeed, been shown above, that currents of 

 high electric force do not travel any faster through submerged con- 

 ductors than feeble currents, but the advantages of the former are 

 that each electric wave represents a larger accumulation of force, 

 and travels consequently to a greater distance before it has so far 

 dispersed as to be no longer capable of producing an effect upon 



