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IV. On the Reduction of Mr. Faraday's Discoveries in Mag- 

 neto-Electric Induction to a general Law. By the Rev. 

 William Ritchie, LL.D., F.R.S., Professor of Natural 

 and Experimental Philosophy in the Royal Institution of 

 Great Britain, and in the University of London. 

 To Sir David Brewster. 



I 



My Dear Sir, 

 N a lecture which I had the honour of delivering before 

 the British Association at the Oxford Meeting, I first 

 pointed out, and illustrated by experiment, a general law, which 

 connects together the splendid discoveries made by Mr. Fara- 

 day on the subject of magneto-electricity. As one of the most 

 essential parts of science is the reduction ot facts to general 

 laws, and as the views which I then developed have only been 

 publ'ished in the Abstracts of the Royal Society*, I have ven- 

 tured to request you to give them a place in your widely ex- 

 tended Journal. I am, my dear Sir, yours truly, 



Wm. Ritchie. 



The law is founded on the universal principle that action 

 and reaction are equal. Thus, if voltaic electricity induce mag- 

 netism under certain arrangements, magnetism will, by simi- 

 lar arrangements, react on a conductor and induce voltaic 

 electricity? Instead of stating the law of magneto-electric in- 

 duction and then illustrating it by experiment, it will be more 

 instructive to arrive at it by a process of induction. 



1. If a piece of soft iron, N S, be made to approach rapidly 

 a voltaic conductor, and at right angles to 

 its direction, the soft iron will be converted 

 into a magnet having its poles developed at 

 N S, according to the direction of the vol- 

 taic influence. If the battery, Z C, be re- 

 moved, and the ends of the wire connected 

 with the zinc and copper plates brought into 

 metallic contact, and if the piece of soft iron 

 be again converted into a magnet by means ot a permanent 

 horseshoe magnet, the wire will have the same voltaic state 

 induced on it as it had when connected with the battery. 



If a temporary magnet be merely a piece ot soft iron having 

 the electricity essentially belonging to it arranged m a parti- 

 cular direction, it is obvious that the motion of the atoms ot 

 the electric fluid will take place in the opposite direction when 

 the iron is ceasing to be a magnet or returning to its natural 

 state. Hence the direction of the voltaic influence induced 

 » Sec Loml. and Edinb. Ptfl, Mag., vol. iii. p, 37-— Edit. 

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