Ih'. Tyndall on Diaina^netism and Ma^necri/stallic Action, 185 



f Looking back to Tables IX. and X., we see that the line 

 which was there most strongly repelled is here repelled most 

 feebly, and vice versa, the change being due to compression. 



I have been careful to make similar experiments with sub- 

 stances concerning whose amorphism there can be but little 

 doubt. A very convenient substance for showing the influence 

 of compression is the white wax used in candles. The substance 

 is diamagnetic. A little cylinder of the wax suspended in the 

 magnetic field set with its axis equatorial. It was then placed 

 between two stout pieces of glass and squeezed as thin as a six- 

 pence ; suspended from its edge, the plate thus formed set its 

 length, which coincided with the axis of the previous cylindei^ 

 axial, and its shortest dimension equatorial. * 



The plate was then cut into little squares, these were laid one 

 Toppn the other and then pressed together to a compact cubical 

 mass. Two such cubes were placed upon the torsion-balance, 

 and the repulsions in the line of compression, and in a line per 

 pendicular to the same, were determined— the former was con^ 

 siderably the greater. 



The pith was scooped from a fresh roll, placed between the 

 glass plates, and squeezed closely together ; after remaining in 

 the vice for half an hour, an oblong was taken from the plate 

 thus formed, and suspended from its edge in the magnetic field ; 

 it set like a magnetic body, with its length from pole to pole. 

 The mass w^as diamagnetic, its line of compression was repelled, 

 and an apparent attraction of the plate was the consequence. 



Fine wheat-flour was mixed with distilled water into a stiff 

 paste, and the diamagnetic mass was squeezed into thin cakes. 

 The cakes when suspended from the edges set always with their 

 longest dimension from pole to pole, the line of compression 

 being equatorial. 



Rye-flour, from which the Germans make their black bread, 

 was treated in the same* manner and with the same result. 



I have an oblong plate of shale from the neighbourhood of 

 Blackburn in Lancashire, which imitates Pliicker^s first experi- 

 ment with tourmaline with perfect exactitude. The mass is 

 magnetic, like the tourmaline. Suspended from the centre of 

 one of its edges, it sets aa:ial; this corresponds to the position 

 of the tourmaline when the optic axis is vertical. Suspended 

 from the centre of the adjacent edge, it sets even more strongly 

 equatorial', this corresponds with the tourmaline when the optic 

 axis is horizontal. If the eyes be closed, and the respective po- 

 sitions of the plate of shale ascertained by means of touch, and 

 if the same be done with Pliicker's plate of tourmahne, it will 

 be impossible to distinguish the one deportment from the other. 



Whoever denies the influence of proximity must be prepared 



