98 DE LA RIVE'S RINGS. 



De la Rive contrived to render conducting wires 

 freely movable, setting them afloat on pieces of 



cork, as represented 

 in Fig. 21. To ex- 

 cite currents through 

 the floating wires A B 

 a, he affixed to their 

 lower ends zinc plates 

 opposite to copper 

 Fis% 2! - plates, and immersed 



them in acid in a basin. They then became 

 electro-magnets. The directions of the currents 

 are denoted by the arrow heads. 



The rings, A B, about which the currents move 

 in similar directions, sail toward each other; 

 while the ring a, which transmits the current in 

 an opposite direction to that about B, is repelled. 

 It gradually turns around, so that the sides about 

 which the currents move in similar directions face 

 each other ; then they are propelled together. 



These pieces of conducting wire, while serving 

 to transmit electric currents, manifest all the 

 characteristic properties of magnets similarly set 

 afloat on pieces of cork by the ancient philoso- 

 phers, as previously described. 



Although a compass needle points its poles, or 

 ends, north and south, apparently crosswise of the 

 terrestria.1 currents from east to west, yet it is to 

 be remembered that the electro-magnetic currents 

 circulate about the axis of a magnet, and not 



