/S. L. Penfield — Stereographic Projection. 9 



every point of which is x° from p. In the figure, x is equal 

 to 28°, hence the circle touches the north and south meridian 

 at the points a and b, respectively at 8°, =36° — 28°, and 64°, 

 = 36° + 28°. It is evident that all possible lines of projection 



5, A and B. 



JV 







h ^>^~ x ~ 









\^ . 



7\/ 



0~A 

 \ a ' 







\ ft ■/ / \^^ \ 





<*f\ 



* 

 \ / 



\36' W° 



Equator^ 



- 























< A 



running from S to the small circle under consideration must 

 be located upon the surface of an imaginary cone, with its 

 apex at S and having a circular base touching the meridian at 

 a and b. Such a cone is an oblique cone, and the plane ab Sis 

 a symmetrical section through it. Continuing the line S a, 

 laying off a distance Sb f ~ 8 b, and joining b b\ a section b b r 



