T. Deighton 



219 



formed by the revolution of a line of force AQPB about the axis AB 

 will vary as: 



tan e cos3 9 (W 

 (since the circumference of the tore in the median plane is 'IvCP oc tan 6) 



sin 6 COS" d (19 



cos2 9 d (COS 9) = i cos3 9. 



Thus the fraction of the total current passing outside any tore oc cos^ 9 

 and the fraction passing inside any tore cc (1 — cos^ 9). 



It follows from this that 35-7 per cent, of the current passes outside 

 the sphere whose poles are the electrodes. 



Proceeding in a similar way we have for a lamina 



1 1 



PX = PY cc 



oc cos 9 



AP AC sec 9 

 if AC is constant. 



Therefore the fraction of the total current passing outside any portion 

 of the lamina enclosed by two lines of force of equal length on opposite 

 sides oi AB varies as 



(1 + cos2^)f/0 = 



cos- 9 d.9 

 "1„ 1 . 



77 



4 



in 2^ 



Table VI. Results of Tray Experiment, Observed and Cahulated. 



Resistance 



As will be seen from Table VI this agrees very well with the results 

 obtained in the experiments ^\'ith the tray of moist sand described above. 



