422 Proceedings of the Royal Physical Society. 



one particular method. No doubt the clinographic projection 

 is on the whole the best. But often it may serve the purpose 

 better if two, or even three, orthographic views of a crystal 

 are made. It seems to me, for example, in the case of some 

 Calcites, that a basal view orthographically drawn may 

 advantageously accompany a clinographic drawing of the 

 crystal as seen from its sides. In the case of some crystals, 

 Miller's plan of giving two orthographic views is an excellent 

 one. All we really require is that the special characteristics 

 of a crystal shall be shown in the clearest manner possible. 

 One worker known to me, who is perfectly familiar with the 

 methods of clinographic drawing, prefers the orthographic 

 method in general, and especially in drawing orthorhombic 

 crystals, and I can certainly answer for the clearness and 

 generally satisfactory nature of his drawings. 



My own method of work in connection with the Scottish 

 Mineral Collection is, first, to make orthographic freehand 

 drawings of each crj'stal in three aspects, keeping always as 

 near to the actual shape of the specimen, even to its irregu- 

 larities of fracture, or of attachment, as closely as possible. 

 Then, if a clinographic drawing will show fully and clearly 

 all the special points, one is thereupon made. 



Clinographic Drawings of Crystals, — The method of making 

 a finished clinographic drawing is based upon the use of a 

 modification of Quenstedt's Linear Projection, as above 

 mentioned. In this, which the reader will find described in 

 Dana's "Text-Book," 1898 edition, p. 547 et seq., the plane of 

 projection, instead of being drawn in plan, is represented as 

 tilted a certain inclination forward and to the right, and the 

 vertical axis, of correct parametral length, is drawn passing 

 in the plane of the paper through the centre of it. On 

 this, as a basis, all the unit forms and most others of 

 common occurrence in the species represented are carefully 

 drawn. Each face is treated as a plane of indefinite 

 extension, which touches the vertical axis at unit length. 

 The zonal points where the traces of two planes meet on 

 the middle plane of the projection (which corresponds to 

 the plane of the paper in the ordinary Linear Projection) 

 are the points which, when connected by lines with the 



