Transparent Bodies hy the Action of Magnetism. 423 



size, form or distance of the armatures. The following Table 

 contains the results of the experiments* : — 



Table III. 



I. The great armatures, 140 millims. in diameter and 50 



millims. thick, being employed. 

 Distance between the ai-matures 50 millims. 

 Battery of twenty elements. 



Rotation produced by sulphide of carbon . + 0° 44'. 

 Rotation produced by the solution . . . —2° 4' 45". 

 Proportion between the first and second"\ „ ^„ 



rotations ^-i'fS6. 



II. The hexagonal armatures being employed. 

 Distance between the armatures 65 miUims. 

 Battery of twenty elements. 



Rotation produced by sulphide of carbon. . +0° 55' 15". 

 Rotation produced by the solution . . . —2° 28' 30". 

 Proportion between the two rotations . . —2-83. 



III. The hexagonal armatures being employed. 

 Distance between the armatures 27 millims. 

 Battery of ten elements. 



Rotation produced by sulphide of carbon . +1° 43' 15". 

 Rotation produced by solution .... —4° 54'. 

 Proportion _2-84. 



IV. The hexagonal armatures being employed. 

 Distance between the armatures 27 millims. 

 Battery of twenty elements. 



Rotation produced by sulphide of carbon . +2° 22' 45". 

 Rotation produced by the solution . . . —6° 31' 30". 

 Proportion —2-74. 



Mean value of the ratios of the rotations . — 2*82. 



Hence we see that the value of the ratio between the two rota- 

 tions is the same in all the experiments. Consequently the 

 negative magnetic rotation of the plane of polarization, like the 

 ])08itive rotation, varies in proportion to the magnetic action. 

 It seemed to me highly probable, by reason of this conformity, 

 that it also varied directly with the cosine of the angle contained 

 between the direction of the magnetic action and that of the ray 

 of light, but I have not performed any experiments on this sub- 

 ject. A thickness of 1 centimetre of the solution of perchloride 

 of iron in wood -spirit, placed upon the apparatus described in 



* Tlie numbers in this Table are corrected for the influence of colour, 

 and for tliat of the glass plates of the case. 



