SECT. XXII. CIRCULAR POLARIZATION. 185 



hol, &c which do not possess circular polarization 

 themselves, the angle of deviation remaining exactly the 

 same as before the mixture. Whence M. Biot infers 

 that the action exercised by the liquids in question 

 does not depend upon their mass, but that it is a mole- 

 cular action exercised by the ultimate particles of mat- 

 ter, which depends solely upon the individual constitu- 

 tion, and is entirely independent of the positions and 

 mutual distances of the particles with regard to each 

 other. These important discoveries show, that circular 

 polarization surpasses the power of chemical analysis hi 

 giving certain and direct evidence of the similarity or 

 difference existing in the molecular constitution of bodies, 

 as well as of the permanency of that constitution, or of 

 the fluctuations to which it may be liable. For example, 

 no chemical difference has been discovered between 

 syrup from the sugar-cane and syrup from grapes. Yet 

 the first causes the plane of polarization to revolve to 

 the right, and the other to the left ; therefore some es- 

 sential difference must exist in the nature of then- ulti- 

 mate molecules. The same difference is to be traced 

 between the juices of such plants as give sugar similar 

 to that from the cane, and those which give sugar like 

 that obtained from grapes. This eminent philosopher 

 is now engaged in a series of experiments on the pro- 

 gressive changes in the sap of vegetables at different 

 distances from their roots, and on the products that are 

 formed at the various epochs of vegetation, from their 

 action on polarized light. 



It is a fact established by M. Biot, that in circular 

 polarization, the laws of rotation followed by the differ- 

 ent simple rays of light are dissimilar in different sub- 

 stances. Whence he infers that the deviation of the 

 simple rays from one another ought not to result from 

 a special property of the luminous principle only, but 

 that the proper action of the molecules must also concur 

 in modifying the deviations of the simple rays differently 

 in different substances. 



One of the many brilliant discoveries of M. Fresne 

 is the production of circular and elliptical polarization by 

 the internal reflection of light from plate glass. He has 

 shown that if light polarized by any of the usual methods 



