M. A. Berlin on Circular Magnetic Polarization, 489 



throughout the whole extent of this circle except in the centre, 

 where it will be somewhat less ; then on the outside of this 

 circle it decreases, but less rapidly than it increased at first, 

 being 13 degrees at the interior portion of the copper ring, 

 7 degrees at the circumference, and 3 degrees at 1 centimetre 

 distance, which corresponds with the initial position of the 

 centre ; finally, it will still be perceptible at more than 1 de- 

 cimetre. 



During this progress the rotation will not have changed di- 

 rection; it will always take place from right to left if the pole 

 is southern, and from left to right if it is northern. These 

 phaenomena are interesting when compared with the directly 

 opposite phaenomena, which are observed in the direction of the 

 line of the poles ; so that with the same position of the flint- 

 glass the rotation may be right or left, null or very powerful, 

 according as it is viewed parallel or perpendicular to the cur- 

 rent. Is it necessary to add, that in all cases the direction of 

 the rotation is always determined by the general law which I 

 have stated at the commencement? 



As I have just observed, that which strikes us at first, 

 when Niirremberg's apparatus is employed, is the great in- 

 tensity of the action observed over the pole. It depends on 

 two causes; one portion must be attributed to the circum- 

 stance that the current acts in the very direction of the lumi- 

 nous ray, instead of being oblique to it; but this especially 

 depends on the reflexion of the ray, which is thus compelled 

 to traverse the magnetized substance twice. This double 

 passage through the quartz would have the effect of causing 

 its natural rotatory power to disappear, by producing two 

 equal rotations of contrary direction, because the rotation of 

 the quartz is independent of the direction in which it is viewed. 

 This is also an excellent method of proving the circular mag- 

 netic polarization in quartz, as it is requisite first of all to de- 

 stroy the atomic polarization in this substance, as remarked 

 by M. Becquerel. In magnetized flint-glass, on the contrary, 

 during the double passage of the light through its thickness, 

 the current acts so as to produce two rotations of the same 

 direction, and consequently the effect is found to be double. 

 I convinced myself of this by making two experiments; the 

 first according to the usual method, by looking directly through 

 the flint-glass, and the second by causing the ray of light to 

 traverse it twice by means of Norremberg's apparatus. The 

 rotation was always twice as great in the second case as in the 

 first. This influence of the reflexion on the intensity of the 

 magneto-rotatory power had already been discovered in a 

 different manner by Prof. Faraday*. 



* Phil. Mag. S. 3. vol. xxix, p. 153. 



