Simpler Methods in Crystallography. 423 



parametral length of the vertical axis, give the direction 

 of intersection of the two faces under consideration. 



The methods adopted in making finished clinographic 

 drawings are somewhat complex, and involve a considerable 

 amount of work. Moreover, they do not seem to be at all 

 adequately described in any of the text-books. For these 

 reasons the subject will be treated here at greater length 

 than is usually given to it. 



The first step in the process is to construct an axial cross, 

 which shall accurately represent the best possible position in 

 which crystals can be viewed so that their front, right side, 

 and top may all be clearly shown. Various methods may 

 be adopted for projecting this axial cross, which, seeing 

 that it forms the basis to all finished clinographic drawings, 

 needs to be made with all possible regard for accuracy. The 

 reader desirous of working out the lines by graphical 

 methods will find these clearly described and illustrated in 

 Dana's "Text-Book of Mineralogy" (new edition of 1898), 

 pp. 547-549, which is reprinted from the older editions of 

 the " System." Even that description leaves a little room for 

 further simplification, which is attempted in the following 

 lines : — Draw a circle of any convenient radius between 2 J 

 inches and 5 inches radius, choosing by preference that scale 

 which is represented upon some good scale of equal parts. 

 As there is usually such a scale of 5 inches on the ordinary 

 6 -inch ivory protractor in a case of instruments, that size, 

 which is not too large for the purpose, may well be chosen. 

 Carefully draw with a fine-pointed pencil two diametral 

 lines exactly at right angles to each other. Mark the point 

 of intersection o, and the right-and-left line bb^ Extend 

 the vertical line beyond the circle '047 of the radius, 

 and mark the extremities cc^. On the circle set off a chord 

 of '054 of the radius in front of B on the right and behind 

 B^ on the left. Sign these points respectively h, V-, and con- 

 nect them by a diametral line. In the bottom left-hand 

 quadrant set off a chord of '457 of the radius from b^, and 

 the same in the opposite direction and quadrant from b. 

 Draw a diametral line from these, and sign the extremities 

 A, A^. Finally, measure off •373 of the radius on OA, oa^, and 



