334 



On the Use of the Globe 



represented on the globe by great circles. As before, the 

 edges are represented by their parallel diameters, and these 

 are designated by the nodes in which they meet the sphere. 

 The azimuth and altitude of each of these nodes is given in 

 the table. As the diameters also pass through the centre 

 of the sphere, the edge is specified both as to direction and 

 situation. 



The first five of these edges actually occur ; the last five 

 are the remaining possible edges which would be formed by 

 the faces produced. They are shown on the globe exactly 

 the same as the others, because, if a number of great circles 

 be drawn on a sphere, every one of them bisects every other. 



In the next table we have the plane angles on face No. o 

 made by pairs of its contiguous faces. Here also we have 

 actually occurring and possible angles. 



If we suppose faces Nos. 1,2, and 4 to be produced, they 

 meet in three edges forming a corner. The three plane 

 angles forming this corner are readily found on the globe. 

 They are the angles contained between the edges (i, 2), (2, 4), 

 and (4, 1 ) on the faces 4, i , and 2 respectively. Hence we have 

 only to measure the arcs on great circles 4, i, and 2 included 

 between their intersections with circles i and 2, 2 and 4, and 

 4 and i respectively; and by measurement they were found to 

 be: plane angle on face i, 108 ; on face 2, 72; and on 

 face 4, 75^. Similarly, if we produce faces i, 3, and 5 to 



