THE 



PHILOSOPHICAL MAGAZINE 

 AND JOURNAL. 



30'" APRIL 1823. 



LII. On Electro-Magnetism. By Mr. J. Tatujm. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



SINCE the discovery of electio-magjietism by Professor 

 Qllrsted*, much new and vahiable information has been 

 given to tlie scientific world by the united labours of various 

 philosophical gentlemen on this very interesting subject. But 

 from the apparetit anomalies attending some experiments, a 

 difference of opinion has been advanced by persons possessing 

 great depth of penetration as well as C(jnsiderable experimental 

 knowledge : for it must be acknowledged tliat, from some ex- 

 periments, it appeared as though the wire connecting the zinc 

 and copper plates of a Voltaic ap])aratus possessed dissimilar 

 poles on its opposite sides. But in oi'der to be satisfied re- 

 specting the accuracy of this appearance, I contrived the ap- 

 paratus so that I could carry the needle all round the wire 

 when it was in a })er))endicular situation ; or, the w/re- round 

 the needle ; or, I could rotate the wire as on an axis, so as to 

 present every side of it to the same part of the needle : by 

 which means I found that the same jmrt of the needle was in- 

 variably attracted or repelletl; so that the whole peripliery of 

 the wire a})pears to possess the same polarity. But as the 

 construction of the common needle does not allow it to rotate 

 in a vertical direction, I could not so satisfactoi'ily investigate 

 the properties of an horizontal wire. I therefore removed the 

 agate cap of a compass, and susj)ended it by an horizontal 

 axis, so that it could rotate freely in a vertical direction ; and 

 by this means I was enabled to examine the magnetic state of 

 die circumference of this wire in a moi-e satisfactory manuei-, 

 whicli ])roved to be of an uniform polarity. 



In the early part of the above investigation, and about the 

 time Mr. laraday's jxiper on this subject apjieared, in whicli 

 he stated that he had discovered tlie needle possessed c/^/// poles, 

 — namely, i'^o north and /tt'o south, on eacli side of the neeille's 

 equator, — I tliought I had observed sixteen poles; namelv, 

 ' F'hil. Ma-, vol. Ivii. pp. \(\,'l{y,\,'lh't,&ic. 



Vol.Gl. No. ;j()0. Ain-il 1823. II h fcmr 



