346 NINETEENTH CENTURY. FT. in. 



a b, Fig. 56, then the north pole turns towards the east. 

 Again, if it runs from north to south below the magnet, in 

 the direction c d, Fig. 55, the magnet will again turn to the 

 west ; while lastly, if it runs from south to north below the 

 magnet, c d, Fig. 56, the north pole turns again to the east. 

 In order to remember these different directions easily, 

 Ampere gave something like the following rule. If a rnan 

 will imagine himself to be standing so that the positive current 

 would come out of his mouth and return by his feet ', the north 

 pole of the magnet will always be on his left-hand side. If 

 you are fond of standing on your head, and will try the 

 positions in Figs. 55 and 56, you will see that this is so the 

 north pole of the magnet will always be towards your left 

 hand. 



Magnetic Currents set up between two Electric Wires.- 

 The next discovery which Ampere made was a very impor- 

 tant one. It was already well known that two magnetic 

 needles will either attract or repel each other according to 

 the position of their poles. Thus, if the north pole of one 

 needle is held towards the south pole of another, they are 

 attracted strongly together, but if the two north poles are 

 brought near together, the movable needle is repelled. Now 

 Ampere argued that if an electric current always causes a 

 magnetic current across itself, then two electric wires side by 

 side will have magnetic currents running across them,and they 

 ought to attract or repel each other as if real magnets were 

 lying between them. And this he proved to be true. He 

 put two wires side by side in such a position that they could 

 move freely, and when he sent an electric current in the 

 same direction through each of them they moved towards 

 each other ; while, if he sent the currents one way through 

 one wire and the other way through the other, they drew 



