.S. L. Penfield — Stereographic Projection. 



115 



Art. IX. — The Stereographic Projection and its Possibili- 

 ties, from a Graphical Standpoint ; by S. L. Penfield. 

 (With Plates II, III and IY.) 



( Continued from page 24.) 



Some Results obtained from the Solution of Spherical Tri- 

 angles by Graphical Methods. — In order to test the accuracy 

 of the methods set forth in the foregoing pages, two right and 

 five oblique-angled triangles were plotted and solved graph- 

 ically. None of the parts of the triangles selected were given 

 to exact degrees, so at the very beginning the points had to be 

 approximately located between the degree graduations of the 

 14 cm divided circle and the scales derived therefrom. 



Case 1.— Given two sides, a = 26° 34' and b = 63° 26', of a 

 right triangle, figure 15. At G construct a diameter, and, by 

 means of protractor No. I, plot the side «, 26° 34/. Lay off 

 the side b, 63° 26', on the divided circle, and then construct a 

 great circle passing through the points thus located, page 15. 

 The angles A and B and the side h of the triangle are thus 

 plotted. A is now measured on the diameter x (stereograph- 

 ically projected great circle) at 90° from A, by means of pro- 

 tractor No. I. B is measured on the great circle s, at 90° from 

 B, by means of protractor No. II, page 18. The side h is 

 measured by protractor No. II. The results of the work are 



as 



follows 



* 

















Calculated 







A 



= 



29° 



12' 







B 



:=r 



11 



24 







h 



= 



66 



25 



Plotted. 



Error. 



29° 10' 



2' 



11 30 



6 



66 25 







