118 



S. L. Penfield — Stereographic Projection. 



the diameter y locate the point p' 31° 25' from C, and con- 

 struct the small circle with radius given by scale No. 2, figure 

 3. Lay off b on the divided circle, and draw the great circle 

 AB, thus completing the triangle. The side c is measured by 

 protractor No. II. The angle A is measured on a diameter 90° 

 from A, by means of protractor No. I. The supplement of 

 the angle B is measured on the great circle s, using protractor 

 No. II, page 18. 



The results are as follows : 





Calculated. 



Plotted. 



Error. 



A 



= 31° 11' 



31° 5' 



6' 



B 



= 83 15 



83 



15 



c 



= 92 48 



92 50 



2 



Case 5. — Given two angles and the included side of an 

 oblique triangle, A = 59° 3', B = 53° 34/, and c = 75° 23', 

 figure 19. Lay off the side c on the divided circle. Plot the 



angles A and B by locating the points p and p\ on the diam- 

 eters x and y, respectively, at 90° from A and B, the point 

 p being 59° 3' and the point p' 53° 34 7 from the divided 

 circle. Using scale No. 1, figure 3, construct the great circles 

 through A and p, and B and^?', thus locating C and completing 

 the triangle. The sides a and b are measured by protractor 

 No. II, and the angle C also by protractor No. II on the great 

 circle s, page 18. 



The results are as follows : 







Calcu 



lated. 



Plotted. 



Error 



a 



Z-Z 



56° 



50' 



56° 45' 



5' 



b 



= 



51 



45 



51 40 



5 







z= 



97 



33 



97 35 



2 



