336 Use of the Globe in the Study of Crystallography 



and 2, it is found to be 53^. The azimuth and altitude of 

 the point of intersection of Nos. i and 2, which have been 

 found by measurement to be 238 and 48^, give the position 

 and direction of the edge made by Nos. i and 2. The altitude 

 48^ is also the inclination of the edge made by two of the 

 faces to the third face. 



Let the plane angle on No. o be 1 20, and the plane angles 

 on Nos. i and 2 be 108 and 90 respectively. By exactly 

 the same construction we find, on measurement, that the faces 

 which fulfil these conditions are inclined o to i at 73^, O to 

 2 at 58, and i to 2 also 58. The edge formed by Nos. i 

 and 2 meets the sphere in 210 azimuth and 58 altitude. 

 The plane angles here assumed are those of the square and 

 the regular hexagon and pentagon. 



If the edge made by Nos. i and 2 lies in azimuth 220 and 

 altitude 50, the base angle being 120, to find the inclination 

 of the faces and the plane angles of i and 2. Great circles 

 are drawn through the points (o, o) and (220, 50) giving 

 circle No. i, and through (120, o) giving No. 2. The 

 angles which they make with each other are then measured 

 and found to be: o to i, 61 ; o to 2, 50 ; and i to 2, 53^. 

 The plane angles are: on No. i, 118, and on No. 2, 97, 

 the angle on No. o being given 120. 



The resources of the globe are inexhaustible ; but the 

 above examples may suffice for the purpose with which this 

 paper was written ; namely, to inform some, and to remind 

 others, of the usefulness of the globe as an instrument of 

 research. 



