488 New Magneto-Optic Phenomena. 



small angle. In another experiment with the polarizer 

 turned through 90° from its original position, the pheno- 

 menon is still exhibited, but the rotation (whose absolute 

 value is the same) is in the opposite direction. 1£ the plane 

 of polarization is parallel or normal to the field, no effect is 

 obtained. I have called this rotation of the plane of polar- 

 ization bimagnetic, in order to distinguish it from the magnetic 

 rotation of Faraday, the term being intended to emphasize 

 the fact that the first phenomenon is different from the second, 

 and depends on the magnetic property of the liquid used as 

 well as on the magnetic field. The bimagnetic rotation may 

 be positive or negative, according as the plane of polarization 

 is rotated so as to recede from or to approach the lines of 

 force. 



I must refer to my original publication for the method of 

 preparing the active liquid. Here it must suffice to mention 

 that in general this may be prepared bj oxidizing, in the wet 

 way, small pieces of iron, and then acting on them with a 

 dilute solution of ferric chloride. According to the nature 

 of the iron oxide employed, the rotation is positive or 

 negative. 



The maximum rotation observed by me was at most 4° 30'. 

 The following is a theory of this effect which has been sug- 

 gested to me by Prof. Voigt. The incident vibrations which 

 are propagated at an angle of 45° to the field may be resolved 

 into two components, one normal and the other parallel to the 

 field. It seems that the magnetic action results in producing 

 a different absorption of these two components, which on 

 leaving the liquid give rise to a resultant vibration in a plane 

 different from the original one. 



The folio wing are a few details regarding this pheno- 

 menon : — 



(a) The bimagnetic rotatory power is different for different 

 colours, according to a law which I have not succeeded in 

 formulating, and which varies from one liquid to another. 



(J)) The rotation is proportional to the thickness of the 

 liquid traversed, provided the rotation be not excessive. 



(c) It increases with increase of field intensity, rapidly at 

 first, but beyond a certain not very intense field strength 

 becomes almost constant. 



(o!) All the specimens of liquids endowed with the power 

 of bimagnetic rotation lose this property to some extent. 



5. I have finally tried to determine whether magnetic 

 double refraction is an instantaneous or a gradual phenomenon. 

 I believe I may conclude that it is really instantaneous, since 

 samples of diaiysed iron became double refracting in a field 

 generated by the discharge of a leyden-iar. 



