S. L. Penfield — Crystal Drawing. 75 



57 58 59 



It is scarcely necessary to state that drawings may be made 

 from gnomonic as well as from stereographic projections, with 

 but slight modifications of the methods just described. 



It is the writer's belief that the average student will find it 

 easier to draw crystals from axes and the symbols of crystal 

 faces, as set forth in the earlier part of this paper, than from 

 the stereographic projection. Cases may arise, however, in 

 which thedatter methods may be found useful, as, for example, 

 in finding the intersections between faces of twin crystals, or 

 in representing some odd shapes which can not be referred to 

 the axes of the crystal systems. 



Mineralogical Laboratory of the 



Sheffield Scientific School of Yale University, 



New Haven, Conn., November, 1904. 



Note.— If any desire to make use of the Engraved Axes, page 43, the 

 Protractor for plotting Crystallographic Axes, page 44, or the Special 

 Triangles, page 53, the writer will be glad to answer any communications 

 and see that the necessary articles are supplied from his laboratory. 



