THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



SEPTEMBER 1855. 



XX. On the Nature of the Force by jvhich Bodies are repelled 

 from the Poles of a Magnet; to ivhich is prefixed, an Account 

 of some Experiments on Molecular Infiuences. By John 

 Tyndall, Ph.D., F.R.S. S^-c.^ 



[With Three Plates.] 

 Introduction. 



FROM the published account of his researches it is to be 

 inferred, that the same heavy glass, by means of which he 

 produced the rotation of the plane of polarization of a luminous 

 ray, also led Mr. Faraday to the discovery of the diamagnetic 

 force. A square prism of the glass, 2 inches long and Oo of an 

 inch thick, was suspended with its length horizontal between 

 the two poles of a powerful electro-maguet : on developing the 

 magnetism the prism moved round its axis of suspension, and 

 finally set its length at right angles to a straight line drawn 

 from the centre of one pole to that of the other. A prism of 

 ordinary magnetic matter, similarly suspended, would, as is 

 well known, set its longest dimension from pole to pole. To 

 distinguish the two positions here refeiTed to, Mr. Faraday 

 introduced two new terms, which have since come into general 

 use : he called the direction parallel to the line joining the poles, 

 the axial direction, and that perpendicular to the said line, the 

 equatorial direction. 



The difference between this new action and the ordinary 

 magnetic action, was further manifested when a fragment of 

 the heavy glass was suspended before a single magnetic pole : 

 the fragment was repelled when the magnetism was excited; 



* From the Philosophical Transactions for 1855, part i.; having been 

 received by the Royal Society October 31, 1854, and read January 25,1855. 

 The Bakeriau Lcctui'c. 



Phil. May. S. 4. Vol. 10. No. 65. Sept. 1855. M 



