462 A. J. Moses — Drawing of Crystal Forms. 



Art. LII. — A Device for Simplifying the Drawing of 

 Crystal Forms ; by A. J. Moses. 



In a former article* I described a graphic method for obtain- 

 ing any axial cross from any projection of the isometric axes 

 by use of a quadrant and scale ; any axial length, sine or cosine 

 being measured on 'the scale and quadrant and laid off on the 

 vertical axis and the proportionate length obtained on any 

 other line through the center by connecting the ends and 

 drawing a line parallel to the connecting line from the point on 

 the vertical axis. Necessarily the vertical axis was either the 

 length of the radius of the quadrant or proportionate dividers 

 were used. 



The method is made still simpler by laying off all measure- 

 ments upon a " scale line " drawn at will from the centre of 

 the axial cross and of a length equal to the radius of the quadrant 

 and by using a metal quadrant shown in fig. 1, the center of 



which is at B. The edge AB and the arc AC are tapered to a 

 thin edge for greater exactness in marking. With AB ten 

 centimeters long the results will be correct within the limits of 

 a drawing. 



Axial lengths are transferred directly from AB to the scale 

 line approximately to the third decimal. Sines and cosines 

 are transferred as follows. If the edge BC and the scale line 

 are made coincident and then, by use of a triangle, the quadrant 

 is slid along in a direction at right angles thereto (BC remain- 

 ing parallel to the scale line) until the scale line cuts the arc at 

 the given degree and approximate minute, the intercept on the 

 scale line will be the sine. Similarly with the edge AB coin- 

 cident with the scale line and a motion at right angles thereto, 

 the intercept on the scale line will be the cosine. 



* School of Mines Quarterly, xv, 214-218. 



