Magneto-optic Properties of Crystals, 1 1 



allowed to cool slowly, until a thin crust gathered on the sur- 

 At this point the crust was pierced, and the molten 

 j, ^ rn eath poured out, thus leaving the complete cry- 

 , oTing round the sides and bottom. Our experi- 



i these crystals corroborate, to the letter, those so 

 described by Mr. Faraday in the Bakerian Lecture 

 ij4 delivered before the Royal Society*. 

 Arsenic. — Our arsenic we obtained at the druggists. It is 

 °il known that this metal is usually obtained by the sublima- 

 $ of its ore, the vapour being condensed in suitable re- 

 vels, where it is deposited in a crystalline form. There is 

 difference of opinion between Mr. Faraday and M. Pliicker 

 >$ regards this metal; the former holding it for diamagnetic, 

 ie latter for magnetic. Several specimens, obtained from 

 'f rent druggists, corroborated the view of M. Pliicker. 

 v were all magnetic. 



oout half an ounce of the metal was introduced into a 

 f*s tube closed at one end and open at the other. About 

 inches of the tube, near the open end, was crammed full 

 copper turnings, and the open end introduced through a 

 iall aperture into the strong draft of a flue from a heated 

 ven. The portion of the tube containing the copper turn- 

 ings was heated to redness, and by degrees the oxygen within 

 the tube was absorbed. The arsenic at the other end was 

 then heated and sublimed, After some time the vapour was 

 allowed to condense slowly, and a metallic deposit was the 

 consequence — the arsenic thus obtained was diamagnetic. 

 The deportment of the crystal is described by Mr. Faraday 

 in the place referred to. 



Antimony. — A difference of opinion exists with regard to 

 the action of this crystal also. Referring to the deportment 

 assigned to it by Mr. Faraday, M. Pliicker writes, " to my 

 astonishment however antimony behaved in a manner directly 

 the reverse. While on the one side a prism of bismuth, 

 whose principal cleavage coincided with the base of the prism, 

 set itself axial ; and on the other side a plate of arsenic, 

 which, on account of its magnetism, ought to stand axial, set 

 itself equatorial; a plate of antimony deviated completely from 

 this deportment, and although the mass was strongly dia- 

 magnetic, set itself decidedly axial." 



M. Pliicker's results differ from those of Mr. Faraday in 

 two particulars; first, a plate of antimony, similar to that de- 

 scribed by M. Pliicker, is found by Mr. Faraday to stand 

 equatorial instead of axial; second, the following phenomena, 

 observed by Mr. Faraday, appear not to have exhibited 

 * Philosophical Transactions, 1849, p. 1. 



