232 Dr. 0. Lodge on the Electrostatic Force between 



by Mr. Boys' kindness, I made in a back room a basty expe- 

 riment on tbe pulses of a Leyden-jar discharge, which was 

 passed either in the same or in opposite directions through a 

 pair of flexible parallel strips of aluminium-foil, looked at 

 through a microscope. 



A fairly distinct effect was observed, its sign being, so far 

 as one could tell, the sign of the electrokinetic effect ; L e. 

 attraction between currents in the same direction, repulsion 

 (more easily observed, because, as it was arranged, nearly 

 four times as strong) between opposing currents. Hence it 

 would seem, so far as this crude observation goes, that pulses 

 in wires do exert their electrodynamic effect. I expected, 

 however, that, by suitably arranging matters, the electrostatic 

 effect of the pulses could be made able to overpower their elec- 

 tromagnetic effect. It is perhaps rather a barbarous plan 

 to consider the two things separately ; but until some one 

 attacks the problem in a powerful manner I have been 

 interested in groping at it, and accordingly make this com- 

 munication. 



First, consider the action of currents in general on each 

 other, and find the ratio between their electrostatic and 

 electrokinetic forces. So far as I know, the electrostatic 

 force between two steady currents is usually overlooked. 



' No advantage in generality is gained by treating two sepa- 

 rate circuits, a movable portion arranged near a fixed portion 

 of one and the same circuit is sufficient. 



Arrange a short length, I, at a distance, a, 

 from a long parallel conductor; with a resist- 

 ance, R, intervening between and P, the 

 middle opposite points of each ; and through 

 the whole send a current, C, up one and down 

 the other. 



Then the difference of potential between 

 the two points is EC, or, with alternating- 

 currents, P C, where P is the impedance of 

 the wire R ; and if the capacity per unit 

 length of the two conductors is called S T , 

 the linear density of charge on each is on 

 the average X^SjPC; a little more above 

 and a little less below it ; but unless the 

 distribution of potential differs greatly from 

 a linear distribution, as when I is comparable 

 to a wave-length, the mean value will serve. 



The electrostatic attraction between the 

 two conductors is 



