THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE, 



[THIRD SERIES.] 



JULY 1850. 



I. Second Memoir 071 the Magneto-optic Properties of Crystals, 

 and the relation of Magnetism and Diamagnetism to Mo- 

 lecular Arrangement. By John Tyndall and Hermann 

 Knoblauch*. 



IN the year 1846 our views of magnetic action received, 

 through the researches of Faraday, an extraordinary ex- 

 pansion. The experiments of Brugmans, Le Baillif, Seebeck 

 and Becquerel, had already proved the power to be active 

 beyond the limits usually assigned to it; but these experi- 

 ments were isolated, and limited in number. Faraday was 

 the first to establish the broad fact, that there is no known 

 body indifferent to magnetic influence, when the latter is 

 strongly developed. The nature of magnetic action was then 

 found to be twofold, attractive and repulsive; thus dividing 

 bodies into two great classes, which are respectively denomi- 

 nated magnetic and diamagnetic. 



The representative of the former class is iron, which, being 

 brought before the single pole of a magnet, is attracted ; the 

 representative of the latter class is bismuth, which, being 

 brought before the single pole of a magnet, is repelled. 



If a little bar of iron be hung freely between the two poles 

 of a magnet, it will set its longest dimension in the line joining 

 the poles ; a little bar of bismuth, on the contrary, will set its 

 longest dimension at right angles to the line joining the poles. 



The position of the iron is termed by Mr. Faraday the 

 axial', the position of the bismuth, the equatorial. We shall 

 have occasion to use these terms. 



These discoveries, opening, as they did, a new field in phy- 

 sical science, invited the labours of scientific men on the con- 

 tinent. Weber, CErsted, Reich and others, have occupied 

 * Communicated by the Authors. 



Phil. Mag. S. 3. Vol, 37. No. 247, July 1850. B 



