1000 ME. E. JENKIN’S EXPEEBIENTAL EESEAECHES ON THE TEANSmSSION 
An example of the confusion arising from interference between successive signals has 
been given by Professor Thomson in his evidence before the Committee appointed by 
the Board of Trade to inquire into the construction of submarine telegraph cables. 
Professor Thomson has also informed the author that the compensation derived from 
experiment, as explained above, is such as theory would demand, but that he has not 
yet verified the exact proportion required between the first and second contacts*. 
Thus every conclusion hitherto stated is in accordance with the mathematical theory, 
and may therefore without hesitation be applied to submerged and extended cables. 
The arrival-curves (fig. 7, Plate L.) do not, however, accurately correspond with that 
given by Professor Thomson. The dotted line shows the calculated curve, drawn so as 
nearly to agree with the experimental curve from 2192 knots, at its origin; the differ- 
ence between the two curves towards the end is very great. The experimental curve 
approaches its limiting height much too slowly after the fii'st few seconds ; one part of 
the curve from 1006 knots is shown on the same figure, and by theory the abscissae of 
the two curves corresponding to equal ordinates should be directly as the squares of the 
lengths. At the origin of the curves this is approximately the case, making a small 
allowance for the constant resistance of batteries and instruments ; but towards the end 
of the curves this is far from being the case. Some of the causes of the discrepancy 
may disappear in straight cables, but meanwhile the constants required in the mathe- 
matical theory cannot be with confidence derived from these curves or Tables. 
It is generally believed that coiling increases the retardation, and the curves obtained 
might be pointed to as confirming this opinion. It is certain that a mutual electro- 
magnetic induction of considerable importance does occur between the different parts of 
the coils f, and probably some part of the discrepancy between the observed and calcu- 
lated curves is due to this cause. But the varying resistance of gutta percha, unknown 
when the theory was framed, also accounts for a considerable difference between the 
results of observation and calculation. The allowance to be made for a constant uni- 
form leakage such as would occur if the resistance of the gutta percha were uniform, 
is described by Professor W. Thomson in the “ Theory of the Electric Telegi'aph ; ” but 
the author of the present paper discovered that the resistance of gutta percha, such as 
was used for the Red Sea cable, increased more than 60 per cent.J during positive or 
* Professor Thomson has also stated that he has long been acquainted with some other modes of pro- 
ducing the required regularity, and one of his methods is alluded to in the evidence before the Board of 
Trade Committee. Vide also Proceedings of the Eoyal Society, Dec. 1856, and Philosophical Magazine, 
1857, where the mathematical principle of the compensation is fully stated. 
t Vide paper read by Professor Thomson at the British Association, Aberdeen, 1859, and letter by Pro- 
fessor yV. Thomson and the author, published in the ‘ Philosophical Magazine,’ 1 861 ; also a letter from 
Mr. E. C. Webb in ‘ The Engineer,’ August 1859. 
i These numbers are calculated from data in. the paper by the author read before the Eoyal Society in 
1860, and published in abstract in the ‘ Proceedings ’ of last year, and in the ‘ Philosophical Magazine ’ for 
1861 ; also in full in the Appendix to the Eeport of the Committee of the Board of Trade on the Construc- 
tion of Submarine Cables, 1861. 
