566 RATIO OF UNITS. 



This method is that with which most experiments have been 

 made ; we may mention, in particular, those of M. Stoletow,* of 

 Professor J. J. Thomson,! and of M. Klemencic.t The condenser 

 of M. Stoletow was constructed of two circular plates, very near 

 each other. Professor Thomson uses the arrangement of 1062, 

 and uses cylindrical condensers with guard-rings. 



M. Klemencic used a differential galvanometer. The current 

 of the battery bifurcates ; one of the parts passes through a resist- 

 ance box and one of the coils, the other goes to a make-and- 

 break, and passes through the second coil in the form of discharges. 

 The resistances are adjusted so that the needle is at zero. The 

 condenser is formed of two circular plates the distance of which 

 can be varied ; the effect of the edges is allowed for by the following 

 formula of Kirchhoff, in which A is the radius of the plates, b their 

 thickness, and e the distance between them, 



A 2 A i6Tr(e + b) b e + ^ 



+ /. ^ + -/. r- + 2 



4^ 4?r I e* e o 



1 



1137. A last method would consist in determining the electro- 

 magnetic capacity C of a condenser by the time / necessary for a 



difference of potential of the two armatures connected by resist- 



y 

 ance R, to pass from a value V to the value V, the ratio being 



determined by an electrometer. We shall then have (985) 



C" t 



The electrostatic capacity c of the condenser being measured 

 directly, it follows that 



* STOLETOW. Journal de Physique [i], Vol. x., p. 468. 1881. 

 t J. J. THOMSON. Transactions of the Royal Society for 1883, p. 707. 

 J KLEMENCIC. Wiener Berichte [3], Vol. LXXXIII., p. 88. 1884. 

 KIRCHHOFF. Berliner Monatsberichte, 1887. Gesammelte Abhandlungen, 

 p. 101. 



