Transmission of Electric Signals through Submarine Cables, 483 



" Experimental Researches on the Transmission of Electric Signals 

 through Submarine Cables." — Part I. Laws of Transmission through 

 various lengths of one Cable. By Fleeming Jenkin, Esq. 



Professor "W. Thomson has in various papers stated and de- 

 veloped the mathematical theory of the transmission of signals 

 through long submarine cables. The present paper contains an ex- 

 perimental research into the same subject. The conclusions arrived 

 at by theory are confirmed by the experiments, and some new facts 

 of considerable importance are established. 



All the observations in this part of the paper were made on the 

 Red Sea cable, when coiled in iron tanks at Birkenhead. 



By observation on a reflecting galvanometer, an arrival-curve was 

 obtained for various lengths of cable with various arrangements of 

 battery. By arrival-curve is meant the curve representing the 

 gradual rise of the current at the remote end of the cable when the 

 near end is put in permanent connexion with the battery. 



The analysis of the various arrival- curves led to the following con- 

 clusions : — 



1. "The electromotive force has no appreciable effect on the 

 velocity with which the current is transmitted. 



2. " The rate of decrease in the current at the remote end, after 

 contact has been made for a given time with earth at the near end, is 

 the same as the rate of increase observed after making contact with 

 the battery at the near end for an equal time." 



"With reference to the use of alternate positive and negative 

 currents as compared with alternate connexion with the positive or 

 negative pole of a battery and earth, 



3. It was found that the "reversals in no way modified the 

 arrival-curve during its increase, nor did they modify the curve 

 showing the decrease of the current." 



The effect of ordinary morse signals was next observed on the gal- 

 vanometer through various lengths of cable. 



The changes in the received current, caused by repeated dots, by 

 repeated dashes, by dots and dashes alternately, and by dots and 

 dashes separated by a pause, were observed at different speeds. 

 Repeated dots, when represented graphically, give an even wavy line , 

 with large amplitudes of oscillation for slow speeds or through short 

 lengths, but rapidly approaching a straight line as the speed of 

 transmission or the length of the cable was augmented. 



If the maximum permanent deflection caused by the battery be 

 called 100, dots sent at the rate of 15 per minute through 2192 

 knots of cable caused oscillations in the received current of 12*7 per 

 cent. ; and sent at the rate of 50 per minute, this caused an oscillation 

 of less than 1 per cent. 



4. From this it was concluded that "on all submarine cables 

 there is a limit to the number of signals which can be sent per mi- 

 nute, a limit which cannot be exceeded by any ingenious contrivance." 



If we continue to call the maximum deflection due to permanent 

 contact 1 00, the mean height of the current observed during dots is 



