THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE, 



^ 



[THIRD SERIES.] 



OCTOBER 1850. 



XXIX. Remarks on the Forces experienced by inductively 

 Magnetized Ferromagnetic or Diamagnetic Non-crystalline 

 Substances, By William Thomson, Professor of Natural 

 Philosophy in the University of Glasgow *. 



THE remarkable law laid down by Faraday in his Me- 

 moir on the Magnetic Condition of all Matter, that a 

 small portion of diamagnetic matter placed in the neighbourhood 

 of a magnet experiences a pressure urging it from places of 

 stronger towards places of weaker force^ is a simple conclusion, 

 derived from the mathematical solution of the problem of de- 

 termining the action experienced by a small sphere of matter 

 magnetized inductively, and acted upon in virtue of its induced 

 magnetism. Without entering upon the analytical investigation, 

 which will be found in a paper " On the Forces experienced 

 by small Spheres under Magnetic Influence; and on some of 

 the Phsenomena presented by Diamagnetic Substancesf," I 

 shall, in the present communication, state and explain briefly 

 the result, and point out some remarkable inferences which 

 may be drawn from it. 



1. Let P be any point in the neighbourhood of a magnet, and 

 let P' be a point at an infinitely small distance, which may be 

 denoted by «, from P. Let R denote the force which a " unit 

 north pole J" if placed at P would experience, or, as it is 



* Communicated by the Author. 



f Cambridge and Dublin Mathematical Journal, May 1847. 



j That is, the end of an infinitely thin uniformly and longitudinally 

 magnetized bar of " unit strength," which is repelled on the whole from the 

 north by the magnetism of the earth ; " unit strength " being defined by 

 the following statement : — 



If two infinitely thin bars be equally, and each uniformly and longitu- 



PhiL Mag. S. 3. Vol. 37. No. 250. Oct. 1850. R 



