RESISTANCE OF ANY GIVEN CONDUCTOR. 205 



between two parallel planes, proceed from the different lines are 



If, in the problem of propagation, we regard the same portions of 

 the lines as sources of electricity, as electrodes, the flows of elec- 

 tricity, or the strengths of the currents, are 



from which we have 



A i = 



and the expression of the potential at P becomes 



V = const- V =const -- L/.r, + I/.r 2 + ..... . 



^ 27JV6 27TT6 \_ l J 



A particularly interesting case is that of two electrodes A l and A 2 

 furnishing equal flows of opposite signs. In this case 



I 1 + I 2 = 0, 

 and 



V = const -- /. . 



The lines of flow are segments of circles passing through the two 

 points A x and A 2 (Fig. 30); the equipotential lines are circum- 

 ferences having their centres on the line A T A 2 and such that these 

 two points are conjugate in reference to each of them. From the 

 remark made above, it is clear that the problem will remain the same 



