210 On the True and False Discharge of a Coiled Electric Cable. 



tent as to necessitate a considerably slower rate of working than 

 will be found pi*acticable after the cable is laid. 



The theoretical conclusion that the "false discharge" would 

 not be observed in submerged cables, has been recently verified 

 by Mr. Jenkin on various lengths of Bona cable up to 100 miles, 

 which he was engaged in recovering, and which, under careful 

 tests, never gave the slightest indication of " false discharge," 

 although, even when the remote end had completely lost insula- 

 tion, they gave not only polarization effects*, but also, in the same 

 direction as these, but distinguishable from them, indications of 

 true discharge. But, in fact, a fortnight before the theoretical 

 conclusion was published by Prof. Thomson at the Aberdeen 

 meeting, a most remarkable and decisive experimental demon- 

 stration of it was published by Mr. Webb, Engineer to the Elec- 

 tric and International Telegraph Company, who had indepen- 

 dently discovered the phenomena which form the subject of 

 this paper, and given substantially the same explanation as that 

 which we now maintain. If there could be a doubt as to the 

 electro-magnetic theory, the following extract from a letter of 

 Mr. Webb's, published in 'The Engineer' of August 26, 1859, 

 is decisive : — 



"It is, however, on making contact at F with earth [that is to 



Fig. 2. 

 Connexions used by Mr. Webb. 



C. Calile. 

 A & B. Galvanometer. 



say, putting what we have called the near end of the cable to 

 earth] that the greatest and most singular difference occurs [be- 

 tween straight and coiled cables]. It will then be seen that the 

 needle at A [that is to say, the needle of a galvanometer in cir- 

 cuit between key and cable instead of between key and earth, as 

 in our experiments], instead of being reversed will continue 



* Of the same nature as those observed by Prof. Wheatstone on his 

 short cables. 



