Transmission of Electric Signals through Submarine Cables. 485 



that the experiments and theory confirm one another, and the con- 

 clusions may be safely applied to the practical case of a submerged 

 and extended cable ; for it is impossible to suppose that results due 

 only to an accidental arrangement of the cable should by chance 

 coincide with the deductions from a defective hypothesis. 



The experimental arrival-curves do not exactly agree with the 

 curve given by Professor "W. Thomson (Proceedings of the Royal 

 Society, 1855. Phil. Mag. 1856). 



The experimental curve approaches its maximum much more slowly 

 than the mathematical curve, and continues to rise 1 or 2 per cent, 

 long after all effects from retardation as given by theory would cease. 



Some of this effect may be due to the mutual influence of the coils 

 of the cable * ; but the greater part of the discrepancy is due to the 

 change of the insulation due to continued electrification, first published 

 by the author in a paper read before the Royal Society in 1859— 60f . 



The identity of the arrival- curve during increase and decrease 

 shows that, 



8. "The apparent increase of resistance of the gutta percha is 

 rather due to an absorption of electricity which is again given out, 

 than to a real change in the conductivity of the material." 



The theoretical and practical conclusions on the effect of repeated 

 signals were next examined. Little change of insulation could take 

 place during the repeated signals, because the greater part of the 

 cable remained continually electrified; and greater coincidence between 

 the experiments and the theory was therefore to be expected. 



The curve expressing the rate at which the amplitude of oscillation 

 in the received current diminishes as the number of signals increases, 

 was constructed from Professor W. Thomson's equations \ ; and the 

 experimental amplitudes with 1500, 1802, and 2192 knots of cable 

 in circuit, were found to coincide in the most accurate manner with 

 this curve — establishing completely the soundness of the mathemati- 

 cal theory. 



9. These results prove beyond all question that " the rate of trans- 

 mission varies as the square of the length, whether by rate of trans- 

 mission be meant that speed at which repeated signals fail to produce 

 any sensible effect, or the rate producing so great an amplitude that 

 common hand-signals can be received without confusion." 



It is also found (when small compared with the total resistance) 

 that, 



10. "The resistance of the battery and receiving instrument pro- 

 duces nearly the same effect as the addition of an equal length of sub- 

 marine cable." 



If the amplitude of oscillation in the received current caused by 

 dots at any one speed through any one straight cable were known, 



* Vide paper read by Professor W. Thomson at the British Association, Aher- 

 deen, 1859. Also paper bv Professor W. Thomson and F. Jenkin, Phil. Mag. 

 18G1 ; also a letter from Mr. F. C. Webb in 'The Engineer,' August 1859. 



f Published in full in Appendix to the Report of the Committee of the Board 

 of Trade on the Construction of Submarine Cables. 



X Vide Proceedings of the Royal Society, 1855. Phil. Mag. 1856. 



