36 Ml'. J. N. Hearder on the Atlantic Cable. 



when passing between tlieir terminals, and sufficient, 1 should 

 consider, to destroy life in an instant, was so reduced when pas- 

 sing through 2500 miles of the Atlantic Cable, that I could just 

 perceive a slight throb in my tongue whilst allowing the shock 

 to pass througli it. 



An attempt was made to obviate the embarrassment arising 

 from the action of the residual charge, by reversing the currents, 

 and upon the following principle : viz., that as the passage of a 

 positive current through the wire charged the internal surface of 

 the gutta percha positively, giving rise to a residual discharge 

 of positive electricity from the wire after the passage of the cur- 

 rent itself, so it was thought that the transmission of a negative 

 current after the positive, instead of another current of the same 

 character, might have the effect of assisting, as it were, in more 

 rapidly exhausting the residual positive charge, and disincumber- 

 ing the succeeding negative current of disturbing influences. This 

 plan partially succeeded, but only partially, since the time saved 

 in the transmission of consecutive signals was but little. It was 

 found, practically, that when these reversals were repeated quicker 

 than at certain intervals, no signals were indicated. I had a 

 remarkable opportunity of testing this peculiar effect whilst ex- 

 amining some of these phsenomena with Mr. Whitehouse. When 

 the conductor of the Atlantic Cable was separated in the middle, 

 and the two ends laid upon the tongue, so that it should form 

 part of the circuit, the effect of the reversals could be easily and 

 curiously distinguished. Each wire produced a sensation, the 

 negative one being the stronger. As the reversals were made, 

 so the characteristic pungent sensation alternately shifted from 

 one wire to the other on the tongue, and as they followed each 

 other more rapidly, so the sensations became less and less dis- 

 tinct. From practice however, added perhaps to a greatly in- 

 creased nervous susceptibility, arising from my want of sight, I was 

 able to appreciate these alternations long after they would have 

 ceased to be indicated by the recording instruments. 



The reason of this partial success appears evident enough, on 

 considering the nature and action of the residual charge. It 

 must be remembered that a wire coated with gutta percha and 

 immersed in water, has a double office to perform, viz. not only 

 to conduct the current to the other end, but to distribute poi'- 

 tions of that current throughout its course to the surface of the 

 gutta percha, for the purpose of charging it after the manner of 

 the Leyden jar; and since the terms positive and negative, when 

 applied to the current, are merely conventional, and only indicate 

 its direction, it is necessary to consider the phsenomena in their 

 relation to these directions. A voltaic battery, then, or any other 

 arrangement which sets electricity in motion, is possessed, accord- 



