M. A. Berlin on Circular Magnetic Polarization, 487 



Rotations. 

 With a tliird placed between the third and fourth"! ^ ' 



reels J 



With two reels placed on either side of the three\ . ^q 



cells J 



3rd. Experiment on Jlint-glass. 



With a very thick flint-glass, of 55 millimetres,! - _ 



placed between two reels J 



With Faraday's flint-glass, of 48 millimetres . . 6 10 

 With two flint-glasses placed at two different in-\ ^^ ^^ 



tervals J 



The two flint-glasses in contact, with two reels\ ^ ^^ 



on either side j 



The last experiment of each series clearly shows that the 

 increase observed in the rotation depends, not on the in- 

 crease in thickness of the magnetized substance, but on the 

 distribution of its different layers in the intervals between the 

 reels. I need not observe that, in employing successively all 

 these intervals during the experiment, the reels remained 

 strictly in the same position, and consequently retained their 

 magnetism intact. 



Thirdly. In a helix perpendicular to a polarized ray, as, for 

 instance, in a vertical reel receiving on its upper base the glass 

 traversed by the light : if this is rotated around the pole, 

 placing it successively on all the radii of the reel, a rotation in 

 the same direction is found on viewing it always from the same 

 surface ; for instance, from that which is turned towards the 

 pole; and this rotation is to the right if the pole is southern, 

 to the left if it Is northern. The rotation again changes di- 

 rection when the glass is viewed from the opposite surface. 



It follows, therefore, that if the glass is viewed placed in two 

 symmetrical positions in relation to the pole, the position of 

 the analysing prism being fixed, we shall observe rotations of 

 contrary directions. Consequently, if employing the horse- 

 shoe electro-magnet, we look through the flint-glass always 

 placed on the line of the poles, but successively at the extre- 

 mities and then in the middle, we should observe, as M. 

 Pouillet did, rotations of the same direction outside the poles, 

 but in the middle a rotation in the contrary direction. 



These positions, where we observe change of direction in 

 the rotation, are separated by others where there is no effect ; 

 the latter are precisely at the poles. But it was seen that in 

 this case a rotation was perceived on looking in the axis of 

 the current, or of the magnet supposed to be perforated in 

 this direction. 



