﻿102 Lord Rayleigh on the Experimental 



The other part of the resistance, R 2 , is that of the system of 

 conductors AO, OC, AB, BO, and OB., the points A and C 

 being considered as the electrodes. Hence 



P(c + a)(y + a) + ca(y 4- a) + yoc(c + a) ... 



2 (c + a)( 7 + a)+£(c + a + 7 + «) ' ' K \ 



" In this expression a denotes the internal resistance of the 

 battery and its connexions, the value of which cannot be 

 determined with certainty; but by making it small compared 

 with the other resistances, this uncertainty will only slightly 

 affect the value of E 2 . 



"The value of the capacity of the condenser in electro- 



magnetic measure is 



T 

 C= [2](K 1+ R 2 )- ■*-•■• ( 5 )" 



Apart from the difference of notation, (5) is the same as 

 the formula arrived at by Prof. Thomson. Maxwell's idea 

 would appear to have been that it makes no difference to the 

 galvanometer in OA whether in AC we have the resistance R 1? 

 which gives the ordinary balance, or the commutator and 

 condenser, provided that the condition be satisfied that the 

 same integral current passes from A to C in both cases |- In 

 considering the fulfilment of this condition we must remember 

 that the difference of potential (A— C) at A and C under the 

 steady current is not the same as that (A'— C) to which the 

 condenser is charged. The latter corresponds to the rupture 

 of AC, so that no current there passes. The condition may 

 be expressed: 



Capacity , A-C . 



t (A ~ bj -~RT' 



and what we have further to consider is the relation between 

 A'-C'andA-C. 



Let E' be the electromotive force which must act in Rj in 

 order to stop the current in it. Then E' = A' — C. From 

 another point of view the zero current in AC may be regarded 

 as the resultant effect of two independent electromotive forces 

 E, E' acting in the system composed of R 2 and the other 



* In Maxwell's statement a and * are interchanged in the first term 

 of the denominator. 



t E. g. in the case of steady currents the introduction of an electro- 

 motive force into AC has no effect, provided the resistance of that brarch 

 be so altered as to satisfy the above condition. 



