344 PLUCKER ON THE THEORY OF DIAMAGNETISM. 



From this way of viewing the subject, a magnetic needle 

 which is directed by the nearest terrestrial pole, while its centre 

 of gravity sustains no sensible action, presented an analogy. 

 If such a needle be attached at its centre to a lever which is so 

 suspended that the whole can rotate freely in a horizontal plane, 

 the needle moves into the magnetic meridian ; and, in order to 

 attain this position, must, according to its original position, 

 either approach or recede from the terrestrial pole. 



12. If we represent to ourselves the prism of tourmaline as 

 consisting of an infinite number of small magnets whose mag- 



perimeiits, which were made for the purpose of explaining and partially 

 imitating the phoenomena presented by crystals. 



" 1 united two bars of soft iron with two bars of brass to a rectangle (Plate V. 

 fig. 7). The bars were 3 millims. thick, and the bars of brass somewhat longer 

 than those of iron. The rectangle was so suspended by silk fibres between the 

 pointed poles that it could swing horizontally, the distance of the poles being 

 so arranged that the whole rectangle did not spring to either. The iron bars 

 were repelled with great force by the poles, and set themselves as far as possible 

 from the latter, parallel to the line which united the poles. 



" The position assumed by the rectangle remained the same when only one 

 pole was permitted to act upon it, or when one of the iron bars was superseded 

 by a brass one. 



" I bored sixteen holes transversely, through a round bar of brass, which was 

 about 50 millims. long and 5 to 6 millims. in thickness, so that the holes were 

 very small, were at equal distances apart, and all lay in the same plane of the 

 axis. Through these I introduced thin iron wires, the protruding ends of which 

 were filed away. Suspended between the poles so that the plane of the wires 

 was horizontal, the bar was decidedly repelled and forced into the equatorial 

 position. When the plane of the perforations was vertical, the bar was attracted 

 and was brought into the axial position. 



" When the iron wires passed through the brass wire at a definite angle with 

 the axis of the latter, the bar took up an oblique position, so that the iron wires 

 were parallel to the line forcing the poles of the magnet. When the plane of 

 the wires was vertical the bar set axial. 



" A spiral of iron- or steel-wire suspended between the poles (Plate V. 

 fig. 8), assumes the equatorial position with great force ; its two halves were 

 repelled by the poles, &c. 



" I also borrow from the same memoir, without the addition of any further 

 observations, figs. 9 to 12 of Plate V., which are intended to exhibit the deport- 

 ment of t(;^urmaline, magnetic antimony, calc-spar and bismuth, between the 

 poles of a magnet. The direction of the optic axis is denoted by an arrow, 

 the directions in which the polarity occurs by small hnes. In imitation 

 of the two first crystals, these lines represent little bars of iron which are 

 inserted in an indiflferent mass ; in the two last crystals, bars of a strongly dia- 

 magnetic substance." 



