562 



the point z is the centre of a zone-circle CMS, and thus also the 

 point of intersection of the zone-axis KQ with the plane of the 

 photograpiiic plate P, tliis being in tig. 2 tiie plane of projection of 

 the stereographical (ignre to the left. 



Fig. 2 Construction for the cliange of the Stereographical Projection of a Röntgek- 

 pattern (to the right: potassiumchloride after Bragg), into the Stereographical 

 Projection of the corresponding reticular planes of the Crystal- structure. 



Let now m be the stereographical projection of the point Q, then, 

 if the polar circle to m is drawn, this circle will contain all points, 

 that are the projections of all tautozonal reticular planes, having 

 KO as their zone-axis. The azimuth of every spot in the plane P 

 and the azimuth of the stereographical pole of each corresponding 

 reticular plane in P always being equal, the place of every one of 

 these stereographical poles on the polar circle just obtained, may be 

 localised by joining the original spot, and to pass this straight line 



