iS'l' M. A. Berlin 07i Circular Magnetic Polarization. 



By means of the above-mentioned apparatus I have been 

 able to make the experiment so as to render it visible at a 

 public lecture. The arrangement presents no other difficul- 

 ties than those resulting from the narrovi^ness of the beam of 

 light traversing the electro-magnet. I therefore removed the 

 diaphragms placed at the extremities of the helices, and was 

 then able to work with a ray of light of two centimetres in 

 diameter. This ray proceeded from a lamp of M. Soleil's 

 construction, placed before one of the reels. It traversed 

 successively a polarizer formed of one large pile of glasses, 

 a Faraday's flint-glass, of 48 millimetres, placed between the 

 two reels and in contact with them, an analyser formed of a 

 large doubly refracting prism, and then a convergent lens 

 which projected it upon a screen. One of the two images of 

 the prism having been extinguished while the current passed 

 in a certain direction, it was seen to reappear as soon as the 

 direction of the current was changed; and it was again ex- 

 tinguished, or rather it was brought to the tint of passage by 

 a suitable rotation of the analysing prism. But the expe- 

 riment is much more striking when a doubly rotating Soleil's 

 plate of quartz is placed behind the polarizer. The lens then 

 projects upon the screen two images of complementary tints, 

 the two halves of which, brought at first to an equality of tints 

 by means of the analyser, change in a contrary direction as 

 soon as the current is altered. On turning the analyser a 

 certain extent, we reobtain an uniformity of tint in each image. 

 This experiment is precisely the same as that of M. Pouillet*. 



The direction of the rotation impressed on the plane of po- 

 larization was correctly recognized by Prof. Faraday, and may 

 be determined in a simple manner. The rotation has the same 

 direction as the current which produces magnetization, or rather 



* Comptes Rendus des Stances de fAcadeviie des Sciences, vol. xxii. p. 1 35. 



