in the Study of Crystallography 



333 



to 66, is applied to circle No. o and slid along it till the 

 pole of the meridian is again in the intersection of the two 

 small circles, the meridian ought to coincide with the circle 

 No. 4, already drawn. This construction was carried out and 

 the resulting great circles fell less than half a degree apart. 

 The coordinates of the plane are (209, 66). Circle No. 5 

 is inclined at an angle of 66| to both its neighbouring faces 

 and is laid down exactly as No. 2. 



After laying down the great circles Nos. o, 1,2, 3, 4, and 5, 

 representing the fundamental face No. o and the five neigh- 

 bouring ones, which by their intersections make No. o a 

 pentagon, the positions and inclinations of faces and edges 

 were taken off with the metrosphere. The measurements are 

 along great circle No. o from one of its intersections with 

 No. i as o of azimuth, and altitudes above or below it. 



These are laid down directly from the data supplied for the 

 crystal, and the small differences of the values thus found on 

 the globe from those intended to be placed on it will give an 

 idea of the precision to be obtained with the particular globe 

 and circles. In the following table we have values derived 

 graphically from this construction for the position and direc- 

 tion of edges formed by the meeting of any two of the faces 



