214 CIRCULAR POLARIZATION. [SECT. xxn. 



by alcohol, turn it to the right. A compensation is effected 

 by the superposition or mixture of two liquids which possess 

 these opposite properties, provided no chemical action takes 

 place. A remarkable difference was also observed by M. 

 Biot between the action of the particles of the same sub- 

 stances when in a liquid or solid state. The syrup of grapes, 

 for example, turns the plane of polarization to the left as 

 long as it remains liquid ; but, as soon as it acquires the solid 

 form of sugar, it causes the plane of polarization to revolve 

 towards the right, a property which it retains even when 

 again dissolved. Instances occur also in which these cir- 

 cumstances are reversed. 



A ray of light passing through a liquid possessing the 

 power of circular polarization is not affected by mixing 

 other fluids with the liquid such as water, ether, alcohol, 

 &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 ex- 

 ercised by the liquids in question does not depend upon 

 their mass, but that it is a molecular action exercised by the 

 ultimate particles of matter, which depends solely upon the 

 individual constitution, 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 

 in 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 essential difference must 

 exist in the nature of their ultimate 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 



