Prof. Thomson on the Electric Telegraph. 159 



between what it would be if the other wires were removed, and if 

 the one used were separated from them by a sheathing of its own. 

 We may therefore apply the theoretical result by taking c something 



between and Hence if "the retardation" agree with 



2-45 1-35 



the time corresponding to a in the diagrams, k must be intermediate 

 between 



^10 , 10 



— 1 — ' ' — ~ — TT ^ — 1 74A ' 



2:i^x(180x5280)^Xlog^(^|j ^X(180X5280)^Xlog^(3J 



or again, if " the retardation" correspond to 9 a, A must be interme- 

 diate between 



and 



^X(180X5280)'^Xlog^ (^ -^ X (180X5280)2Xlog,Q) 



I think it quite certain that what was observed as the retardation 

 must be in reality intermediate between a and da of the diagrams. 

 Hence the true value of k for 1 foot of the wire must be between the 

 greatest and least of the preceding estimates, that is, between 



and 



108X109 176X10'o 



But the value of K (the "resistance" in British absolute electro-mag- 

 netic measure of 1 foot of the wire) must, according to Weber's obser- 

 vations on copper, be about 99810, or nearly enough 100,000*. Hence 

 a (the number of electro-statical units in the electro-magnetic unit) 



being equal to -/— , must be between 104,000,000 and 419,000,000. 



According to the observations of Weber, Joule, and others, the 

 quantity of water decomposed by a current of unit strength during 

 the unit of time, that is, by the electro-magnetic unit of electricity, 

 is very exactly -^^^th of a grain. Hence from 2,000,000 to 8.200.000 

 electro-statical units are required to decompose a grain of water. A 

 positive and a negative electro-statical unit at a foot distance attract 

 one another with a force of ^ of the weight of a grain. Hence if 

 the electricities separated in the decomposition of a grain be concen- 

 trated in two points a foot asunder, they will attract with a force of 

 more than 10 tons, and less than 42 tons ! Faraday long ago conjec- 

 tured that less electricity passes in the greatest flash of lightning than 

 in the decomposition of a drop of water, which is now I think ren- 

 dered very probable. 



The expression for the force, in British dynamic units, between 



* See a paper "On the Application of the general principle of mechanical effect 

 to the Theory of Electromotive Forces, &c.", published in the Philosophical Ma- 

 gazine, Dec. 1851. 



