Nov. 1 845.] Rotation of a Ray of Light by Magnetism. 297 



A person looking for the phenomenon for the first time would 

 not be able to seent with a weak magnet. 



21 54-. The character of the force thus impressed upon the 

 diamagnetic is that of rotation ; for when the image of the 

 lamp-flame has thus been rendered visible, revolution of the 

 eye-piece to the right or left, more or less, will cause its ex- 

 tinction ; and the further motion of the eye-piece to the one 

 side or other of this position will produce the reappearance of 

 the light, and that with complementary tints, according as 

 this further motion is to the right- or left-hand. 



2155. When the pole nearest to the observer was a marked 

 pole, i. e. the same as the north end of a magnetic needle, 

 and the further pole was unmarked, the rotation of the ray 

 was right-handed ; for the eye-piece had to be turned to the 

 right-hand, or clock fashion, to overtake the ray and restore 

 the image to its first condition. When the poles were re- 

 versed, which was instantly done by changing the direction of 

 the electric current, the rotation was changed also and became 

 left-handed, the alteration being to an equal degree in extent 

 as before. The direction was always the same for the same 

 line of magnetic force (2149.). 



2156. When the diamagnetic was placed in the numerous 

 other positions, which can easily be conceived, about the mag- 

 netic poles, results were obtained more or less marked in ex- 

 tent, and very definite in character, but of which the phaeno- 

 mena just described may be considered as the chief example : 

 they will be referred to, as far as is necessary, hereafter. 



2157. The same phenomena were produced in the silicated 

 borate of lead (2151.) by the action of a good ordinary steel 

 horse-shoe magnet, no electric current being now used. The 

 results were feeble, but still sufficient to show the perfect 

 identity of action between electro-magnets and common mag- 

 nets in this their power over light. 



2158. Two magnetic poles were employed end-ways, i. e. 

 the cores of the electro-magnets were hollow iron cylinders, 

 and the ray of polarized light passed along their axes and 

 through the diamagnetic placed between them : the effect was 

 the same. 



2159. One magnetic pole only was used, that being one end 

 of a powerful cylinder electro-magnet. When the heavy glass 

 was beyond the magnet, being close to it but between the 

 magnet and the polarizing reflector, the rotation was in one 

 direction, dependent on the nature of the pole ; when the dia- 

 magnetic was on the near side, being close to it but between 

 it and the eye, the rotation for the same pole was in the con- 



