466 PARTICULAR CASES. 



by saying, that two currents which form an angle with each other 

 attract if they both approach, or both recede from the apex of the 

 angle or the common perpendicular, and that in the contrary case 

 they repel. 



The experiment is made by bringing an unlimited rectilinear 

 current near the bottom of a movable rectangular frame traversed by 

 the current. The movable frame turns so as to receive, on its 

 negative face, the maximum flow of force which proceeds from the 

 rectilinear current. There is no simple expression for the work of 

 any given displacement ; but the total work corresponding to the 

 displacement of the frame, from the position in which its plane is 

 perpendicular to the current, to that in which it becomes parallel, is 

 proportional to the flow of force which traverses the frame in the 

 second case. If a Q and 1 are the distances from the unlimited 

 current of the two sides of the frame parallel to it, and b the length 

 of one of these sides, we have 



and the electromagnetic work is equal to 2 1 !'/. . 



O-Q 



These movements are easily accounted for by supposing the 

 currents replaced by equivalent magnetic shells, and considering the 

 actions of these shells. 



We may arrive at the same object on Faraday's plan, by con- 

 sidering the lines of force and their distribution in the field. The 

 figured lines of force of the field resulting from the various systems 

 near each other, are closer in certain regions than in others. If we 

 represent these lines of force (105) as elastic threads exposed to a 

 strain in the direction of their length, and to a repulsion in the 

 direction perpendicular to this, we shall have a very definite idea 

 of the relative motion which they tend to produce. 



482. APPARENT REPULSION OF Two CONSECUTIVE ELEMENTS 

 OF CURRENT. This important experiment of Ampere consists in 

 putting the two poles of a battery in connection with two rectangular 

 troughs containing mercury, and separated by an insulating division. 

 A copper wire is bent so as to form two horizontal legs floating 

 on the mercury, and a cross piece (in the form of a bridge) which 

 connects the two former. When the battery circuit is closed, the wire 

 is seen to glide along the surface of the mercury, and to recede from 

 the points by which the current enters. 



