THE 

 LONDON, EDINBURaH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIElVCE. 



[FIFTH SERIES.] 



NOVEMBER 1877. 



XLIV. On the apparent Alteration in Weight of a Wire 

 placed East and West and traversed hy an Electric Current. 

 By Professor J. W. Mallet, F.R,S, * 



THE observations of Gilbert, about tbo end of the sixteenth 

 century, that the earth behaves as a great magnet, the 

 beautiful theory of Ampere, according to which all magneti- 

 cally polar bodies may be viewed as owing their peculiar cha- 

 racter to electric currents circulating round the particles, 

 equivalent in effect to circular currents surrounding the mass 

 as a whole in planes at right angles to the magnetic axis, and 

 the facts observed by Ampere as to mutual attraction and re- 

 pulsion of conductors conveying currents of electricity serve, 

 as is well known, to explain the directive action exerted, under 

 all circumstances of relative position, by the earth upon ordi- 

 nary magnets, and also upon movable conductors through 

 which ordinary electric currents are passing. 



Thus a magnetized bar of steel, if freely suspended, sets 

 itself (magnetic) north and south, and may be considered as 

 surrounded by circular electric currents which on the lower 

 side of the bar are moving from east to west. And, in like 

 manner, a helix of wire, when traversed by a current from a 

 galvanic battery, if left free to move, sets itself with its axis 

 north and south ; and in such position, if Ave adopt the usual 

 definition for the direction of the battery-current, this current 

 is found to be from east to west on the lower side of the 

 spiral, thus establishing parallelism with the assumed earth- 



* Communicated by the Author. 

 FUL Mag. S. 5. Yol, 4. No. 26. 'Nov, 1877. Y 



