i9o6] MICHELSON— FORM ANALYSIS. Ill 



Classification of Forms. 

 I. Symmetrical. 

 II. UnsymmetricaL 

 I. Symmetrical forms. 

 Congruence of parts by 



A. Rotation through i8o° (Odd Symmetry). 



B. Reflection in plane (Even Symmetry). 



C. Rotation -j- Reflection (Partial Symmetry). 



1. Radial Symmetry. (Corresponding points equidistant from 



radiant.) 



2. Axial Symmetry. (Corresponding points equidistant from 



a fiducial line.) 



3. Plane Symmetry. (Corresponding points equidistant from 



plane.) 



1. Radial Symmetry. 



01. Central Symmetry. (Corresponding points on 

 straight line through center.) 



b. Ovoid Symmetry. (Radiant in axis but not central.) 



c. Ex centric Symmetry. (Radiant not in an axis.) 



2. Axial Symmetry. 



a. Centraxal Symmetry. (Corresponding points on 



same perpendicular through axis.) 



b. Dorsiventral Symmetry. (Corresponding points not 



on same perpendicular. ) 



3. Plane Symmetry. 



a. Triplanar Symmetry. 



b. Biplanar Symmetry. 



c. Bilateral Symmetry. 



. The foregoing general systems of symmetry might be carried 

 out in greater detail. For instance, the central symmetrical forms 

 might be subdivided into (i) Spherical, (2) spheroidal, (3) ellip- 

 soidal, (4) monoclinal, and (5) triclinal. So also the triplanar sym- 

 metrical forms may be classified into (i) Isometric, (2) quadratic, 

 ( 3 ) rhombic ; and the centraxial forms according to the number of 

 similar parts into which an equatorial section may be divided, 

 (w = 2, 3, 4, 5 . . . 00). 



