THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



JUNE 1865. 



LVII. On the Retardation of Electrical Signals on Land Lines. 

 By Fleeming Jenkin, Esq.* 



[With a Plate.] 



IN various papers on the theory of the electric telegraph, 

 Professor W. Thomson has investigated the effect produced 

 on electrical signals by lateral induction, and has deduced the 

 laws by which, when certain constants peculiar to each circuit 

 are known, we can calculate the modifications that will occur in 

 any signal, or series of signals, in consequence of transmission 

 through that circuit. The nature of these modifications, which 

 are most marked in the case of submarine cables, may be 

 described as follows. 



1. The abrupt well-defined electrical changes produced at the 

 sending-end of the circuit, by making or breaking contact with 

 the battery, are replaced at the receiving-end by changes more 

 or less gradual. Thus, when a current is sent into a cable by 

 suddenly completing the circuit, no sensible effect whatever is at 

 first observed at the further end (supposed in connexion with the 

 earth). After a little while a weak current arrives, and this gra- 

 dually increases until, after a certain time more or less long, a 

 maximum is reached, when, if the insulation were perfect, the 

 received current would be equal to that sent. 



2. If the signals be sent in such rapid succession that sufficient 

 time does not elapse between each change of contact for the re- 

 ceived current to acquire this maximum and again fall to zero, then 

 the total magnitude of the change at the receiving-end will be 



* Communicated by the Author, being an extension of a paper read at 

 the Meeting of the British Association at Bath. 



Phil Mag. S. 4. Vol. 29. No. 198. June 1865. 2 E 



