Stereographic and G?iomonie Projections. 



213 



Certainly the methods of getting both a plan and a parallel- 

 perspective from either a stereographic or gnomonic projection 

 appeal strongly to one at first, both because of their simplicity 

 and the doing away with the multiplicity of construction lines 

 which frequently are needed in drawing from axes. To con- 

 vince himself of the relative advantages of the different 

 methods of drawing crystals, the writer has taken special pains 

 to experiment with those explained in this paper, and it is his 

 belief that most persons, especially beginners, will find it 

 easier to draw from axes, while at the same time finished 



a* 



Figures 11 and 12. Development of a parallel-perspective of augite, 

 drawn on a plane parallel to s, 111. 



drawings will in most cases be completed more quickly and, 

 probably, with greater accuracy. It certainly would seem as 

 though with the axes constantly before one, they must be of 

 value to a student in developing the symmetry of a crystal 

 figure during the process of drawing. When it comes to a 

 complicated problem, such as one in the triclinic system, it 

 may be questioned whether it is easier to incline the axes and 

 draw from them, or to make either a stereographic or gnomo- 

 nic projection and draw from it : The determination of such a 

 question would depend somewhat upon the data at hand, and 

 largely upon one's familiarity or facility with either the one 

 or the other method. Certainly, as is often the case, having 

 made either a stereographic or gnomonic projection for the 

 purpose of study, it would be easier to draw from the projec- 

 tion than to plot the inclined axes and draw from them. 

 Every one who is at all interested in crystal drawing would do 

 well to become familiar with the methods based on the use of 



