Electricity in a uniform plane conducting Surface. 483 



s, shift of the slider D. 



2a, or AB, distance between the poles. 



p, radius of the circle of contact of the electrodes, or half the 



diameter of the brass rods. 



r, radius of the tinfoil disk. 



S, thickness of the disk. 



k, specific conductivity of the material of disk. 



T ., . , AG.BF.A'G.B'F, L , , on N 



Ju, the expression log 10 g \iu Tt/n (see equation (20 a), 



39, Parti.), 



p* . AT . B'G 



C, the constant 



log e lQ 



2ttk8' 



The following relations hold good among the above quantities : 



and 



whence 



K+#=-- (§50) 



R = CL (§§ 38 and 39, Part I.), 

 s — e#=eCL. 



First set of Resistance experiments, April 1874. 



e was practically constant and =5*147, p = *163, e#=2'42. 



Case 1. Two equal electrodes on the ed°-e of a circular disk 

 (Part I. Plate IX.). 





! 





s— ex 



Number of 

 experiments. 



r. 



2c. 



s. 



log— 

 P 



13 



( \ 26-20 



68-80 



301 



13 



18-83 

 1316 \ I 15-465 



65-42 



305 



9 



62-08 



30-0 



12 



13-466 



59-47 



29-8 



16 



U 10-185 



5705 



30-6 



17 



f 1 15-224 



61-66 



30-1 



6 



7-62 U ' 675 

 7 bJ 1 1 10-35 



58-02 



300 



10 



57-20 



30-4 



5 



L 8-78 



56-60 



31-3 





Weighted 1 



nean 



...30-29 



2/7 



In this case L = 41og — by formula (13), §§ 25 & 39, Parti., 



and therefore -— =4Ce= const. : the mean value 30*29 gives 



, 2a 

 log 7 



2C = 2*943. 



212 



