Masterpieces of Science 



iron disk. Both of them had found that when 

 in rotation the body exercised a peculiar action 

 upon the magnetic needle, deflecting it in a man- 

 ner which was not observed during quiescence; 

 but neither of them was aware at the time of the 

 agent which produced this extraordinary deflec- 

 tion. They ascribed it to some change in the 

 magnetism of the iron shell and disk. 



But Faraday at once saw that his induced 

 currents must come into play here, and he imme- 

 diately obtained them from an iron disk. With 

 a hollow brass ball, moreover, he produced the 

 effects obtained by Mr. Barlow. Iron was in no 

 way necessary: the only condition of success was 

 that the rotating body should be of a character 

 to admit of the formation of currents in its sub- 

 stance: it must, in other words, be a conductor 

 of electricity The higher the conducting power 

 the more copious were the currents. He now 

 passes from his little brass globe to the globe of 

 the earth He plays like a magician with the 

 earth's magnetism. He sees the invisible lines 

 along which its magnetic action is exerted and 

 sweeping his wand across these lines evokes this 

 new power. Placing a simple loop of wire round 

 a magnetic needle he bends its upper portion to 

 the west: the north pole of the needle immedi- 

 ately swerves to the east: he bends his loop to 

 the east, and the north poles moves to the west. 

 Suspending a common bar magnet in a vertical 

 position, he causes it to spin round its own axis. 

 Its pole being connected with one end of a gal- 

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