on the Polarity of the Diamagnetic Foh:e, 179 



The deflection here indicates ordinary magnetic polarity. The 

 action was very powerful. When swiftly moving in any direc- 

 tion, a change in the position of the cylinder instantly checked 

 the magnet in its course, brought it to rest, or drove it forcibly 

 in the opposite direction. The numbers 185 and 990 mark 

 indeed the utmost limit between which it was possible for the 

 magnet to move ; here it rested against the helices. 



Two glass tubes were filled with red oxide of iron and exa- 

 mined. The action of the poles of these cylinders upon the 

 magnets was so strong, as to efface, by the velocity imparted to 

 the magnets, all distinct impression of the numbers on the scale. 

 By changing the position of the tubes within the helices, the 

 magnets could be driven violently through the field of view, or 

 could be held rigidly against the respective helices. As in all 

 other cases, the centre of the cylinders were neutral points, and 

 the two ends of each were poles of opposite qualities. The po- 

 larity was of course the same as that of iron. 



A small quantity of iron filings was kneaded thoroughly in 

 wax, and a cylinder formed from the mass. Its deportment was 

 also very violent, and its polarity was of course just as clear and 

 pronounced as that of a solid cylinder of iron could possibly be. 



Sulphate of iron was next examined : the crystallized sub- 

 stance was enclosed in two glass tubes and tested in the usual 

 manner. 



XXII. 



Cylinders of Sulphate of Iron. 

 Length 4*5 inches. Diameter 0*7. 



Current direct. Current reversed. 

 Position 1. 510 510 



Position 2. 600 370 



Position 3. 700 220 



The red ferroprussiate of potassa is a magnetic salt ; with this 

 substance the following results were obtained : — 



XXIII. 



Cylinders of red Ferroprussiate of Potassa. 

 Length 4*5 inches. Diameter 0*65. 



In this case also the crystallized salt was enclosed in glass 

 tubes. 



N2 



