S. L. Penfield—Stereographic Projection. 



readily caught by the eye. The protractor is printed on trans- 

 parent celluloid. At the center there is a small hole, and at 



be 



CD 



a ,2 



> V 



CD i 



- 2 



be 



m O 



o> CD 



'o *-3 



+= bfi 



CD 

 be CD 

 CD ^ 



bjo o 



□ £ 



bC £ 



6 



o 

 03 



So 



*= c72 



the ends of the semicircle the celluloid is cut away to the exact 

 line of the diameter. The chief use of this protractor is to 

 find the great circle which passes through any two given points 



