﻿Frederick Guthrie on Magnetism and Diamagnetism. 17 



of bismuth may be finely ground in a porcelain mortar for an 

 hour, and the finer portion shaken through a linen bag containing 

 a lump of the metal. The residue which refuses to pass is em- 

 ployed. This is strewn uniformly and not too thickly on a sheet 

 of white glazed paper, which is laid upon the poles of the electro- 

 magnet. On exciting the magnet and gently tapping the paper, 

 figures of accumulation are produced, such as are shown in 

 fig. 3, a and b. If glass be used instead of paper, the relative 

 position of these lines and the edges of the magnet can be ex- 

 amined. In a the poles are nearer together than in b. In a 

 the continuous lines represent the edges of the poles as seen 

 through the glass. The dotted masses show the distribution of 

 the powder. In b the magnetic poles are omitted, but are re- 

 presented by dotted lines, which consist of finely pencilled ridges 

 of powder accumulated immediately above the edges of the iron 

 poles. When the poles are as near together as they are in a } no 

 such lines are seen. These lines disappear on continually tap- 

 ping the paper or glass, and therefore, I conclude, are not to be 

 attributed to any region of attraction, or to any exceptional 

 structure in the bismuth, but may be compared to the ridge of 

 powder which will rest on the edge of a blunt wedge pointing 

 vertically upwards when powder is strewn on it. Lying, in fact, 

 immediately above the region of maximum repulsion, they are in 

 unstable equilibrium. 



If the paper (for the following experiment paper is preferable to 

 glass) supporting the uniformly distributed bismuth-powder be 

 moved horizontally, one or two little ridges of powder are formed 

 (according to the nearness of the poles) , which remain stationary 

 as the paper passes beneath them, the particles shifting and 

 rolling so as to maintain the same positions with regard to the 

 poles beneath. With care a whole sheet of paper may be passed 

 beneath. These rolling ridges are best seen when the poles are 

 at a distance intermediate between the distances in a and b, so 

 that there is only a narrow isthmus of bismuth-powder situated 

 equatorially between the poles, as in fig. 3 c. The ridges are the 

 isthmus of powder, and the accumulation p or q (fig. 3 c) , ac- 

 cording as the paper is moved towards q or p respectively. 1 

 have not found any further structure in the distribution of the 

 bismuth-powder analogous to the structure in the arrangement 

 of particles of iron under similar conditions — no indication, in 

 fact, of lines of diamagnetic force. The bismuth separated from 

 the nitrate by zinc, or from the subnitrate by zinc and sulphuric 

 acid, has not in my hands proved so good for showing these effects 

 as the powdered metal. These diamagnetic phenomena may 

 easily be transferred to the screen in the usual way. 



December 3, 1870. 

 Phil Mag. S. 4. Vol. 41. No. 270. Jan. 1871. C 



