Henry's Chemistry. 343 



S., or in the magnetic meridian, but will be suddenly diverted from 

 its natural position and place itself at right angles to the wire, its 

 northern extremity becoming somewhat elevated, and its southern 

 depressed. If we now reverse the direction of the electric current, 

 we shall at the same time reverse the position of the needle; its 

 south end will veer round to the spot formerly occupied by the 

 N., and vice versd in regard to its, north end. From this statement 

 we may in some measure anticipate what would happen, when the 

 wire is placed vertically instead of horizontally, in respect to the 

 needle, — but we shall not enter into the details of position, least 

 we perplex the main argument. For all this and much more im- 

 portant information connected with it, we are indebted to Professor 

 Oersted. It might have been expected that a wire, under the influ- 

 ence of common electricity, would affect the needle in the same 

 way as the galvanic conductor; Sir H. Davy instituted experiments 

 which proved this to be the case, and he showed that to commu- 

 nicate strong and permanent polarity to a steel bar, it became ne- 

 cessary to attach it transversely to the electrified wire, or to place 

 it in that position at a small distance from it. His researches led 

 him moreover to a number of curious facts connected with the 

 communication of magnetism by electricity, and his paper is full of 

 curious suggestions connected with this inquiry*. 



We now come to Dr. Wollaston, who, upon hearing of Oersted's 

 discovery, immediately proceeded to convince himself of its cor- 

 rectness, and to examine intojthe theory of the phenomena ; the re- 

 sult of his inquiries led him to infer, if we mistake not, that a cur- 

 rent or vortex of magnetism was put into motion round the axis of 

 the conducting wire, consequently, that no fixed magnetic poles 

 could be observed ; but that the pole of a magnet, on approaching 

 the conducting wire, would cause it to attempt to revolve upon its 

 own axis, in a direction dependent upon that of the electric current. 

 Hence, the idea of magnetic rotation, which has since given rise to 

 such an amusing multiplicity of apparatus, certainly first occurred 

 to Dr. Wollaston ; but having established his very ingenious and 

 satisfactory theory, and having convinced himself and most of his 

 friends, of its adequacy to the explanation of the phenomena, he 

 seems to have dropped the inquiry, which in respect to rotation 

 was pursued upon other grounds by Mr. Faraday, who constructed 

 the first apparatus in which the pole of a magnet was made to revolve 

 about the axis of a wire-transmitting electricity. In relation to this 

 subject, we refer our readers to his papers in this Journal-)-, and to 

 his " Historical statement respecting Electro-magnetic Rotation. J" 



In the course of last year Dr. Siebeck of Berlin, showed than the 

 electricity excited by heating compound metallic bars, might be 

 rendered evident by its effect upon a magnetic needle, and Messrs. 



* I'/til. Tram. 132). 1 Vol. xii. v>.74mid 410". J Vol, xv. p, 288. 



