314 Dr. Faraday's Researches in Electricity. [Series xix. 



to the magnetic line ; and being limited to this plane, it can 

 be changed in direction by a reversal of the direction of the 

 inducing force. The direction of the rotation produced by 

 the natural state is connected invariably with the direction 

 of the ray of light; but the power to produce it appears to be 

 possessed in every direction and at all times by the particles 

 of the fluid: the direction of the rotation produced by the 

 induced condition is connected invariably with the direction 

 of the magnetic line or the electric current, and the condition 

 is possessed by the particles of matter, but strictly limited by 

 the line or the current, changing and disappearing with it. 



2332. Let m, in fig. 3, represent a glass cell filled with oil 

 of turpentine, possessing naturally the power of producing 

 right-hand rotation, and a b a polarized ray of light. If the 

 ray proceed from a to b, and the eye be placed at b, the rota- 

 tion will be right-handed, or accord- Fig. 3. 

 ing to the direction expressed by the 

 arrow-heads on the circle c ; if the ray 

 proceed from b to a, and the eye be 

 placed at a, the rotation will still be 

 right-handed to the observer, i. e. ac- 

 cording to the direction indicated on 

 the circle d. Let now an electric cur- 

 rent pass round the oil of turpentine 

 in the direction indicated on the cir- 

 cle c, or magnetic poles be placed so 

 as to produce the same effect (2155); 

 the particles will acquire a further / 

 rotative force (which no motion / 

 amongst themselves will disturb), and " 

 a ray coming from a to b will be seen by an eye placed at b 

 to rotate to the right-hand more than before, or in the direc- 

 tion on the circle c; but pass a ray from b to «, and observe 

 with the eye at a, and the phenomenon is no longer the same 

 as before ; for instead of the new rotation being according to 

 the direction indicated on the circle d, it will be in the con- 

 trary direction, or to the observer's left-hand (2199). In fact 

 the induced rotation will be added to the natural rotation as 

 respects a ray passing from a to b, but it will be subtracted 

 from the natural rotation as regards the ray passing from b 

 to a. Hence the particles of this fluid which rotate by virtue 

 of their natural force, and those which rotate by virtue of the 

 induced force, cannot be in the same condition. 



2233. As respects the power of the oil of turpentine to 

 rotate a ray in whatever direction it is passing through the 

 liquid, it may well be, that though all the particles possess 



