ABSTRACTS OF SCIENTIFIC PAPERS 347 



VI. E.<- r - rlnitntal Resvnrh':* n (he Transmission of Electric Signals 

 through long Submarine Cables. Part I. 'Laws of Transmission 

 th rough various Lengthsofone Cable;' ' Philosophical Transactions 

 of the Royal Society,' 1862 ; Abstract in 'Proceedings of the 

 Royal Society,' June 19, 1862, vol. xii. p. 198. 



In 1855 Sir W. Thomson had published the mathematical theory 

 of the transmission of electric signals, and had exhibited the retard- 

 ing effect of electrostatic capacity and resistance by a curve showing 

 the gradual rise with respect to time of the current in the remote 

 instrument when the end operated on was put and kept in connection 

 with the battery. By experiments on the Red Sea Cable while 

 stored in Messrs. Newall's works in 1859, Mr. Jenkin verified the 

 form of this ' curve of arrival,' using as the receiving instrument the 

 marine mirror galvanometer of Thomson, whose quickly vibrating 

 needle allowed it to respond accurately to the variations of current. 

 ' When the key was pressed down the spot of light remained appa- 

 rently motionless for a short but sensible time, then shot along the 

 scale, moving rapidly at first but gradually losing speed, until at last 

 it moved very slowly to a maximum deviation, at which it remained 

 quite still : these movements truly showed the gradual change of 

 the received current from nothing to a maximum, a change requiring 

 50 seconds for its completion.' This was with a length of 2,168 

 knots, and experiments with other lengths of cable verified Thomson's 

 law that the retardation varies as the square of the length. The 

 results also demonstrated that, in accordance with the theory, the 

 retardation is independent of the electromotive force employed to 

 transmit signals, and that if after contact with the battery the 

 sending end of the cable be put to earth, the rate of decrease of 

 current at the remote end is the same after any interval as the rate 

 of increase in the arrival curve after an equal interval from the 

 beginning of contact with the battery. The experiments were further 

 directed to supply practical data with regard to the possible speed of 

 signalling through cables, a subject then attracting attention especially 

 as bearing on the scheme for a new Atlantic line. Observations 

 were made of the amplitude of fluctuation in the received current 

 produced by the sending of dots and dashes (short and longer appli- 

 cations of the sending battery), the amplitudes being expressed as 

 percentages of the whole strength which the received current would 

 reach if the sending battery were kept in contact with the line for a 

 time long enough to allow the current to become sensibly steady. 

 A limit to the possible speed of signalling was demonstrated by 



