On the Symmetry of Homogeneous Structures. Ill 



circular polarization and structure the very obvious con- 

 clusion suggests itself that since circular polarization is 

 essentially an enantiomorphous property, if it is traceable to 

 arrangement of parts, the structures in which it occurs must 

 be enantiomorphous, i. e. not identical with their own mirror- 

 images. 



Now if we adopt the conclusion, reached in my paper just 

 referred to, that the partitioning which achieves the separation 

 of a crystal into individual molecules must be one w r hich is 

 compatible with the coincidence-movements (Deckbewe- 

 gungen) of the structure*, it is evident that, when a structure 

 identical with its own mirror-image undergoes such a parti- 

 tioning, the fragments produced will either themselves be 

 identical with their own mirror-images, or will occur in equal 

 numbers in two kinds which are enantiomorphs. And that 

 in the former case there will be no enantiomorphism, and that 

 in the latter the effect of such a property of one kind of 

 fragment will, so far as the general mass is concerned, be just 

 cancelled by the similar property, of opposite hand, of the 

 other kind of fragment. 



We see therefore that we may confine our attention to those 

 types of homogeneous structure which are enantiomorphs, 

 not only when dealing with crystals, but also when considering 

 those cases where the substances displaying the property in 

 question are in one of the amorphous states. 



If circular polarization is in some way connected with 

 structure, the following general principles may be laid 

 down : — 



I. Circular polarization is due to the existence of certain 

 arrangements of parts or particles of a structure, and these 

 arrangements, which will be designated effective configurations, 

 are of enantiomorphous form. 



II. Absence of the property in a substance may be due 

 either to the absence of effective configurations, or to the 

 presence in equal numbers of two opposite kinds, whose effects 

 just cancel one another, the arrangement of parts displayed by 

 one kind being generally enantiomorphous, or nearly so, to 

 that presented by the other kind. 



Let us now endeavour to arrive geometrically at a classi- 

 fication of homogeneous structures according to the effective 

 configurations which they contain, both when unbroken and 

 when dislocated, which shall be parallel to the classification 

 given above of substances possessing the property of circular 

 polarization. 



* Min. Mag. 1896, xL p. 130. 

 K 2 



