ABSTRACT OF PROCEEDINGS. XXIX. 



The certificate of one candidate was read for the third 

 time, of three for the second time, and of one for the first 

 time. 



The following gentleman was duly elected an ordinary 

 member of the Society, viz : — 



Simpson. D. 0., m. inst. ce.; North Sydney. 



Three volumes, 118 parts, 4 reports and 2 pamphlets, 

 total 127, received as donations since the last meeting, 

 were laid upon the table and acknowledged. 



The following note was read and explanatory remarks 

 made upon the several exhibits shown : — 



" Note on some simple Models for use in the Teaching of 

 Elementary Crystallography," by W. G. Woolnough, 

 d.sc. [Communicated by Prof. T. W. E. David, b.a., 



F.R.S.] 



Dr. Woolnough exhibited models to illustrate the con- 

 nection between the number of faces in a crystal " form " 

 and the elements of symmetry of the group to which the 

 crystal belongs. He explained briefly that all crystals are 

 symmetrical bodies, the symmetry being due to a regular 

 repetition of similar faces with respect to planes, axes, 

 and a centre of symmetry. Planes of symmetry divide 

 crystals into parts which bear the same relation to one 

 another as an object and its reflection in a mirror. With 

 respect to axes of symmetry, the repetition of faces is 

 rotational in character. Planes of symmetry are therefore 

 represented in the models by mirrors suitably arranged, 

 and crystal faces by triangles of cardboard. The mirrors 

 are so fixed that the multiple reflection of the card repro- 

 duces the shape of the most general form possible in the 

 crystal group. In this way it is very strikingly shown 

 that in the normal groups of the cubic, tetragonal, hex- 

 agonal, and rhombic systems are closed forms of 48, 16, 24 



