486 Messrs. G. C. Foster and 0. J. Lodge on the Flow of 



The flow-lines for this case are indicated in Part. I. (Philoso- 

 phical Magazine, S. 4. vol. xlix.) Plate X. fig. 9, where the circle 

 with centre C corresponds with the edge of the disk. In order to 

 get the theoretical resistance for this arrangement, additional 

 poles, of the same signs as A and B respectively, must be assumed 

 at the points A' and B' ; so that, if the conducting sheet were 

 unlimited, the circle with centre C would coincide with a line 

 of flow : that is to say, A' and B' must be on the prolongations 

 of the radii through A and B respectively, and at the following 



distances from the centre, CA' = 7^—, CB' = -pr=r (see Part I. 



CA CB v 



§§ 36 and 38). Taking A and B as the middle points of the 



circles of contact made by the two electrodes, we have (loc. cit.) 



L_1 ° 8 p 2 .AA'.BB' ; L- C; 3C - 333 - 



The values of AB' and A'B in the above expression were found 

 by laying down on paper, to any convenient scale, the actual 

 positions of the poles from the data AB, CA, CB, CA', CB', and 

 then measuring the distances AB' and A'B. This is a quicker 

 process than the corresponding calculation. 



Case 4. One electrode at the centre, the other touching Fig- 4. 

 the edge (as at b, fig. 4) . 



r=13 # 43 centims., p = *163 centim., #='38. 



Number of 

 experiments. 



AB 



= ? — p. 



s. 



e. 



e 



R 



r-p 

 v3.p 



7 



1327 



913 



1-038 



841 



4-80 



The poles being assumed to be the centres of the circles of 

 contact made by the electrodes, 



L becomes 3 loj 



11 



V 



'P.. 



p 1 7 '—p 



3C; 2C = 3-20. 



