Masterpieces of Science 



On interrupting the current, a whirl of the needle 

 in the opposite direction occurred. It was only 

 during the time of magnetization or demagnetiza- 

 tion that these effects were produced. The in- 

 duced currents declared a change of condition 

 only, and" they vanished the moment the act of 

 magnetization or demagnetization was complete. 

 The effects obtained with the welded ring were 

 also obtained with straight bars of iron. Whether 

 the bars were magnetized by the electric current, 

 or were excited by the contact of permanent steel 

 magnets, induced currents were always gener- 

 ated during the rise, and during the subsidence 

 of the magnetism. The use of iron was then 

 abandoned, and the same effects were obtained 

 by merely thrusting a permanent steel magnet 

 into a coil of wire. A rush of electricity through 

 the coil accompanied the insertion of the magnet ; 

 an equal rush in the opposite direction accom- 

 panied its withdrawal. The precision with 

 which Faraday describes these results, and the 

 completeness with which he denned the bound- 

 aries of his facts, are wonderful. The magnet, 

 for example, must not be passed quite through 

 the coil, but only half through, for if passed 

 wholly through, the needle is stopped as by a 

 blow, and then he shows how this blow results 

 from a reversal of the electric wave in the helix. 

 He next operated with the powerful permanent 

 magnet of the Royal Society, and obtained with 

 it, in an exalted degree, all the foregoing phe- 

 nomena. 



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