﻿16 Frederick Guthrie on Magnetism and Diamagnetism. 



powder arranges itself immediately above the poles in a manner 

 which need not be represented in a diagram, because the lines 

 of accumulation are identical with the edges of the poles, as in 

 fig. la. No especial precaution is required for the produc- 

 tion of this effect. The powdered crystalline sulphate should 

 be dried for a few seconds above a lamp on a sheet of paper. 

 The effect is shown well if black glazed paper is employed, or a 

 thin sheet of mica or of glass such as is used for mounting mi- 

 croscopic objects. The image of the magnetized sulphate of iron 

 may be thrown on a screen in the usual way. As might be an- 

 ticipated, no lines indicating lines of magnetic force are exhibited. 



§ 2. Magnetism of solution of Sulphate of Iron. — This is usu- 

 ally shown by placing the solution in a watch-glass, or on a sheet 

 of mica resting on the two poles. The visible effect is, I think, 

 more striking if the points of the poles, of the shape in fig. 1, 

 are brought within about one eighth of an inch of one another, 

 and two or three drops of the solution suspended between the 

 poles in contact with both (fig. 2 a) . The liquid mass will find a 

 position of equilibrium resulting from its weight, cohesion, and 

 adhesion to the iron. On exciting the magnet, the liquid mass 

 is seen to rise so as to collect around the upper edges of the 

 poles, as in fig. 2 b. A motion of half an inch can be easily 

 produced in this way. The shadow of the poles and liquid is 

 easily thrown on the screen. 



§ 3. Pseudodiamagnetism of Iron. — This can be well shown by 

 punching two or three hundred circular disks out of a sheet of 

 tinned iron, punching a hole in the centre of each, piling them 

 one on the top of the other with a disk of paper between each, 

 passing a brass rod down the central holes, and screwing the 

 whole tight with a nut. The whole may be hung on a stirrup 

 of paper. The compound rod presents the appearance of a 

 simple iron cylinder. When at some distance above the poles of 

 a powerful permanent or electromagnet, it assumes, for well- 

 known reasons, the equatorial position. If brought near to the 

 poles it sets axially. 



§ 4. Diamagnetism of Bismuth. — This effect is usually shown 

 either by the equatorial adjustment of a rod of the metal, or by 

 the simple repulsion from a pointed magnetic pole of a pellet of 

 the metal. The diamagnetism of bismuth may be elegantly 

 shown by bismuth-powder. The powder should be neither too 

 fine nor too coarse. If too coarse, the flat facets of the bis- 

 muth crystals hinder motion ; if too fine, the powder, though 

 quite dry, is prone to cake togther in little hillocks, which col- 

 lectively resist the individual repulsion of their particles — per- 

 haps for the same reason that the rolling of two wheels on a 

 plane is hindered when the wheels are in contact. Half an ounce 



