490 M. A. Berlin ofi Circular Magnetic Polarization* 



The change of rotation with the direction in which it is 

 observed establishes between the magnetized flint-glass and 

 quartz a difference which is rendered still more perceptible by 

 the experiments just cited. However, that is nearly the only 

 difference. The dispersion of the planes of polarization for the 

 different colours is the same in the two bodies. I have proved 

 it in the following manner. 



With the flint-glass placed between the two poles of the 

 electro-magnet under the most favourable conditions to pro- 

 duce a great rotation (29 degrees), I counterbalanced this ro- 

 tation by the contrary effect of a plate of quartz of the requi- 

 site thickness, which is easily obtained with M. Soleil's com- 

 pensator. The system was then perfectly neutral, and would 

 remain so in every position of the analyser, if the quartz and 

 magnetized flint-glass acted in the same manner on the light, 

 which is, in effect, what I have observed in all the different 

 kinds of flint-glass I have experimented with. 



Let us now examine the various circumstances which cause 

 the magnitude of the rotation to differ. 



The nature of the bodies should rank first. The differ- 

 ences are considerable in the various kinds of glasses ; they 

 are less perceptible in liquids, and indeed, according to some 

 experimenters, all solutions have the same rotatory power. 

 Thus Prof. Faraday (in 2185 of his memoir) considers as 

 probable that, in aqueous solutions, the [ruling] rotative 

 matter is the water, and not the other substance. But this 

 opinion will no longer be entertained, when we observe in the 

 first place that the most energetic liquids are precisely those 

 which are anhydrous; and secondly, that among the dissolved 

 bodies there are some which increase the rotatory power of 

 the water, and others that diminish it. Moreover, on increasing 

 the proportion of water in one and the same solution, the 

 rotatory power is seen gradually to approach to that of pure 

 water, — a conclusive proof of the influence of the substance in 

 solution. Alcoholic solutions lead to the same result, 



I will here enumerate a few of the numerous experiments 

 made on this subject. The concentration represented by 1 is 

 that of the most saturated solution ; i represents the degree of 

 concentration of the same solution diluted with water, and so on. 



I . Rotations produced by some anhydrous liquids. 



Rotation of 

 Name of liquid. Thickness, 



Centim. 

 Bichloride of tin .... 1 

 Sulphuret of carbon ... 1 

 Sulphuret of carbon ... 8 

 ProtochJoride of phosphorus 1 



