certain Poitits in Magneto-Electricity. 309 



other side of that pole : and these statements are corroborated 

 by others. (Sect. 101, &c.) 



But Mr. Sturgeon's plate, in your Number for July (fig. 16, 

 17), gives this cun-ent reversed, the other circumstances being 

 the same ; and the current the same, the rotation being re- 

 versed. 



It is also shown by Dr. Faraday Sect. 220, 222), that a 

 magnet held in the direction of the earth's axis, unmarked 

 pole up, and rotated with the earth, or unscrew, yields posi- 

 tive electricity at its extremities, and negative at the centre; 

 and that a copper cylinder revolving round the magnet pro- 

 duces the same result; and that the rotation being reversed, 

 the electricities are also reversed. 



But in a plate of Mr. Sturgeon's very commodious electro- 

 magnetic apparatus (Ann. Phil. N. S. No. 12, p. 359), with 

 an explanation, it appears that a magnet, unmarked* pole 

 up (fig. 1), subjected to positive electricity at the centre (for 

 in a single pair with a liquid the copper pole is so), and ne- 

 gative electricity at the poles, immediately rotates screw or 

 with the sun. And this is confirmed by fig. 8. of the same 

 plate, where a copper cylinder, on the same pole, subjected 

 to positive electricity at the pole, and negative below, rotates 

 unscrew, or with the earth. Now according to the statement 

 above, this rotation produces positive electricity at the pole ; 

 and the rotation of the magnet just described determines po- 

 sitive electricity to the equator. In all other cases positive 

 electricity repels positive and attracts negative ; but here it 

 produces, in both cases, those motions by which electricity of 

 the same name is brought to the same point, instead of those 

 which, by determining the opposite electrical state there, would 

 have satisfied this attractive property. Even the repulsion pro- 

 duced by the first iew turns would seem likely to stop and 

 revert the motion, yet no such thing occurs. 



If these cases have cost others of your readers so much per- 

 plexity as they have me, a rationale from either Dr. Faraday 

 or Mr. Sturgeon is a desideratum. ' 



To the former gentleman I would also suggest the expedi- 

 ency of creating a few new words, expressive of the various 

 conditions of electro-magnetic circulation. There has seldom 

 occurred a case in which they are more needed ; and I need 

 not point out to him geological and mineralogical synonymy 

 as a vocabulary which has a great many to spare. 



• In that particular magnet neither pole u marked ; but the letter N 

 being affixed to the marked and S to the unmarked pole of a liorseshoe 

 magnet on tlie same plate (fig. b), there can be no doubt about their 

 meaning in the figure in question. 



