S. L. Penfield — Stereographic Projection. 



135 



not accustomed to deal with spherical surfaces and their projec- 

 tions, it would seem, on looking at a map in Mercator's projec- 

 tion, that the course should be due west, and that an east wind 

 would be most favorable. Steaming or sailing thus, however, 

 one would be traveling along the arc of a small circle. In stereo- 

 graphic projection, figure 29, the small circle S. 6 7 ., crossing all 



29 



11° 30' 



meridians at 90°, is drawn. The shortest course between Lis- 

 bon, Z., and Delaware Bay, D.B., is, however, the great circle 

 G.C., passing as far north as 43° 6'. Sailing on this great circle, 

 a vessel should be pointed 21° 4' (plotted 20° 57') north of west 

 on leaving port, and should gradually change its course so as to 

 cross the intermediate 43° 15' meridian due west, and then pro- 

 ceed south of west. The distance traveled on the great circle is 

 48° 38' (plotted 48° 50'), equal to 2,918 nautical miles, while the 

 distance on the small circle is 2,982 nautical miles, a difference 

 of 64 miles. It is not probable that a steady wind would be an 

 east one swirling around the pole along the arc of a small circle, 

 but, rather, it would be far more likely to travel along the arc 

 of a great circle, crossing the different meridians at slightly 

 different angles. It seems to the writer that these relations, as 

 plotted in stereographic projection, must be far easier to com- 

 prehend than if plotted on any other projection. 



