500 M. A. Berlin on Circular Magnetic Polarization. 



from the equations which give y or z. We shall have, for 

 example, for a:=0, 



^' — ^ ^~^^ 

 c ~ y 1— r®'* 

 or 



d _^ l—r" 1 + r^~^ 

 7 ~T' 1— r*'* 1+r^-*" 



The following table has been formed in this manner : it 

 contains the coefficients of magnetic polarization of the differ- 

 ent substances experimented with, compared with the flint- 

 glass of Prof. Faraday. 



Faraday's flint-glass 1*00 



Guinant's flint-glass 0*87 



Matthiessen's flint-glass 0-83 



Very thick flint-glass (from the Conservatoire) 0*55 



Common flint-glass 0*53 



Bichloride of tin 0*77 



Sulphuret of carbon 0*74' 



Protochloride of phosphorus 0*51 



Chloride of zinc dissolved 0'55 



Chloride of calcium dissolved 0*4-5 



Water 0*25 



Ordinary alcohol of 36° Beaume 0*18 



^ther 0-15 



I ought not to conclude without remarking, that all the pre- 

 ceding experiments merely relate to the action of electro- 

 magnets upon exterior substances. When the flint-glass ex- 

 perimented with, instead of being outside the electro-magnetic 

 coil was placed in the interior, I did not observe the rotation. 

 I have noticed a very faint one when the second coil was 

 brought near to the first; but this action was very consider- 

 ably less than that which this second coil would have produced 

 upon the same flint-glass placed at the same distance exter- 

 nally. These negative experiments are not opposed to those 

 of Prof. Faraday, for they were not made under the same cir- 

 cumstances. 



If Prof. Faraday has observed a rotation in flint-glasses 

 placed in helices, still it was very faint; again, the inter- 

 position of iron nuclei only increased it when they were longer 

 than the helix; and lastly, this interposition diminished, on 

 the contrary, the rotation when the interior iron cylinder, 

 having the same length as the helix, had at the same time a 

 convenient thickness (§ 2209 of his memoir). Thus in a 

 helix of 673 millimetres in length, of 121 millimetres in ex- 



