4-92 M. A. Berlin on Circular Magnetic Polarization. 



will be seen that if we submit to the influence of a single pole 

 increasing thicknesses of the same substance, the rotation will 

 increase with the thickness up to a certain point, beyond 

 which it will remain constant, an increase of thickness only 

 producing layers which are no longer influenced. 



It is likewise evident, that if the substance is submitted to 

 the contact action of two poles of constant equal force, the 

 effects will only be doubled, and that in consequence the law 

 will still be the same. 



But on interposing fresh strata between the poles, it becomes 

 requisite to separate them more and more, which somewhat 

 diminishes their intensity by decreasing the influence which 

 they exert one on the other. Three cases may then occur ; 

 either this diminution of intensity will compensate the eff*ect 

 produced by the increase of thickness, or it will have a more 

 feeble influence, or lastly, it will preponderate. 



In the first case, the rotation will be independent of the 

 thickness ; in the second, it will increase with the thickness 

 up to a certain point, beyond which it will remain constant ; 

 and lastly, on the third hypothesis, it will attain a maximum, 

 beyond which it will decrease, hut ^without returning to zero^ 

 the two poles always producing effects which conjoin ; so that 

 the extent of the rotations will be twice the effect produced by 

 a single pole. 



It will be seen from the following table that the two first 

 cases may occur with M. Becquerel's electro-magnet, where 

 the variation of the poles of the keepers must be considerable. 

 Substances experimented with. Thickness. Rotations. 



mm. o , 



Flint-glass of Faraday ... 18*3 18 20 



Flint-glass of Faraday . . . 48*3 25 5 



Very thick flint-glass .... 55*1 22 30 



Very thick flint-glass . . . . IIO'S 23 30 



Distilled water 10*0 2 00 



Distilled water 20'0 3 30 



Distilled water 30*0 4 20 



Distilled water 80-0 4 30 



Distilled water 130'0 5 00 



Distilled water 155*0 5 00 



If instead of always bringing the poles in contact with the 

 magnetized substance, they are left at the same distance, by 

 placing between them a gradually increasing number of strata, 

 the rotation will be seen to increase in a continuous manner 

 until the thickness is equal to the distance of the poles. Again, 

 if these poles are sufficiently removed from the various strata 

 of the substance, so that the variations of their distance do not 

 produce perceptible variations in their rotations, the action 



