58 



S. L. Penfield — Crystal Drawing. 



of a crystal may be had. Without question, in many and per- 

 haps the majority of cases, figures in orthographic projection 

 would be far more helpful to beginners, especially if studied 

 in connection with models, than the ones so commonly used 

 which are in clinographic projection alone. An architect in 

 working out the details for any structure would never think of 



27 



28 



submitting to a builder a plan alone, or only an elevation : 

 Two kinds of figures are considered as necessary, plans and 

 elevations, and in like manner students of crystallography need 

 figures drawn in two projections in order to derive the full 

 benefit from them. 



Position of Figitres. — If orthographic and clinographic pro- 

 jections are to be used together there is some choice as to the 



position in which the figures 

 should be placed. Taking barite 

 as an example : If an ortho- 

 graphic projection alone were 

 employed there is no question 

 but that the drawing should be 

 orientated as in figure 27, with 

 the direction of the a and o 

 axes parallel respectively to the 

 vertical and horizontal edges 

 of the page. Provided two pro- 

 jections are used, however, if 

 the clinographic, figure 28, is 

 placed to one side of the ortho- 

 graphic, or directly below it, the 

 apparent connection between 

 the two figures is not at all evident : To place them thus is 

 in violation of the principles of mechanical drawing and pro- 

 jection, and it is hard to realize that figures 27 and 28 are 

 representations of the same crystal. Placed as in figure 29, 

 however, it takes but little study to understand how the two 

 projections are related. It is true that it may at first seem 

 strange to see the orthographic projections skewed around at 



