EXPERIMENTS ON AMPERE'S LAWS. 699 



bottom of the vessels which contain it. When the ends g and i are 

 now connected with the poles of a battery, the current can traverse 

 the whole length of wire of which the square is formed, while the 

 conductor itself can rotate easily. The narrowness of the small 

 opening of the glass tube is necessary to keep the end of the wire 

 which hangs within it in the middle of the mercury ; if the tube 

 were not contracted at the top, the wire would always press against 

 the side and the frame would not move easily. 



The smaller square which is held by the wooden strip in the hand, 

 may be connected with another battery if a sufficient number of 

 elements are at disposal ; or, more simply, one battery only (of at 

 least two cells) is used, and one of its terminals is connected with 

 the wire i, fig. 352 A, the'other with the wire Jc of the smaller square, 

 while the other free wire of this square is connected with the wire g 

 by a wire about O m> 5 long. In the figure the wire i is supposed 

 to be connected with the positive pole of the battery. 



When the movable conductor I is brought near to 

 the fixed conductor II, as in fig. 352 J., both being 

 traversed by the current in the direction of the arrows, 

 it will be distinctly seen that attraction takes places 

 between the vertical sides near to one another ; the 

 square I begins to rotate so that the side m approaches 

 the side n. 



When the conductor II is held, as at B in fig. 352, 

 in a position in which the sides m and 0, which are near 

 each other, are traversed by currents in opposite 

 directions, m is repelled by o. 



Finally, if one square is placed so within the other 

 that their planes are at right angles to one another, as 

 at C in the figure, I will rotate until both squares have 

 the position shown at D. In this case portions of the 

 current intersect in the horizontal sides of the square, 

 and the action takes place in accordance with the pre- 

 vious law of intersecting currents ; but it must not be 

 overlooked that in our arrangement the effect is also 

 partly due to the vertical portions of the current which 



