132 ANNUAL OF SCIENTIFIC DISCOVERY. 



ON THE CRYSTALLINE POLARITY OF BISMUTH. 



WE find in the Philosophical Transactions for 1849, Part L, a long 

 paper by Prof. Faraday, "On the Crystalline Polarity of Bismuth 

 and other Bodies, and on its Relation to the Magnetic Form of Force." 

 The author states, that in preparing cylinders of bismuth, by casting 

 them in glass tubes, he had often been embarrassed by the anomalous 

 magnetic results which they gave, and that, after a. close investigation, 

 he has referred the effects to the crystalline condition of the bismuth. 

 If bismuth be crystallized in the ordinary way, and then a crystal, or 

 a group of symmetric crystals, be selected and suspended in the mag- 

 netic field between horizontal poles, it immediately either points in a 

 given direction, or vibrates about a given position, as a small mag- 

 netic needle would do ; and if disturbed from this position, it returns 

 to it. On re-suspending the crystal, so that the horizontal line, which 

 is transverse to the magnetic axis, shall become the vertical line, the 

 crystal then points with its maximum degree of force. If it be again 

 suspended so that the line parallel to the magnetic axis be rendered 

 vertical, the crystal loses all directive force. This line of direction, 

 therefore, which tends to place itself parallel to the magnetic axis, the 

 author calls the magnecrystallic axis of the crystal. It is perpendic- 

 ular or nearly so, to the brightest and most perfect of the four cleav- 

 age planes of the crystal. Whether this magnecrystallic axis is 

 parallel or transverse to the magnetic axis, the bismuth is in both 

 cases repelled from a single or the stronger pole ; its diamagnetic 

 relations being in no way affected. If the crystal be broken up, or if 

 it be fused and solidified, and the metal be then subjected to the action 

 of the magnet, the diamagnetic phenomena remain, but the magne- 

 crystallic results disappear, because of the confused and opposing 

 crystalline condition of the various parts. If an ingot of bismuth be 

 broken up, and fragmentary plates selected which are crystallized 

 uniformly throughout, these also point; the magnecrystallic axis be- 

 ing, as before, perpendicular to the chief plane of cleavage, and the 

 external form, in this respect, of no consequence. 



The position of the crystal in the magnetic field is affected by the 

 approximation of extra magnets or of soft iron ; but the author believes 

 this to result, not from any attractive or repulsive force exerted on the 

 bismuth, but only from the disturbance of the lines of force, or re- 

 sultants of magnetic action, by which they acquire, as it were, new 

 directions ; and as the law of action which he gives is, that the line 

 or axis of magnecrystallic force tends to place itself parallel, or as a 

 tangent, to the magnetic curve, or line of magnetic force, passing 

 through, the place where the crystal is situated, so the crystal changes 

 its position with any change of direction in these lines. 



Crystals of antimony, arsenic, native crystals of iridium and osmium, 

 and crystallized titanium and "tellurium, gave similar results, but in 

 different degrees. Crystals of zinc, copper, tin, lead, gold, &c., gave 

 no signs of being magnecrystallic. Crystals of sulphate of iron are 

 very strongly affected by the magnet according to this new condition, 

 and the magnecrystallic axis is perpendicular to two of the planes of 



