48 



the case of crystals, as will be demonstrated more in detail later on. 



The fact of the occurrence of two different forms for every symme- 

 trical object of this kind, which forms are related to each other as 

 mirror-images, is known as enantiomorphism ; and the two possible 

 forms are called enantiomorphous with respect to each other. 



The phenomenon of enantiomorphism and of enantiomorphous 

 arrangements in space, is one of the most important facts in the 

 whole domain of physical and chemical research, as we shall after- 

 wards show in detail. Fig. 52 relates to eventually occurring 

 crystalforms in chemical substances, as an illustration of two 

 enantiomorphous polyhedra. 



12. With the aid of the devices employed in this chapter, 

 we have succeeded in finding out all possible types of symmetrical 

 groups of the first order; i. e. of all symmetrical figures which can 

 be made to coincide with themselves by rotations alone. 



We can now use these groups, as we shall see, as a basis for the 

 deduction of all those other groups, which possess also symmetry- 

 properties of the second order. This will be shown more exactly 

 in the following chapter. 



