24:8 Penfield — Use of the Stereographic Projection for 



ing was plotted with much care on a large scale, hence the con- 

 struction of the figure may be regarded as reasonably exact. 

 It represents the lines of projection extending froin P to a 

 plane tangent to the sphere at a point antipodal to P, which, 

 in this case, is the intersection of the equator with the 



Diagram for illustrating the principle of the stereographic projection upon 



a tangent plane. 



meridian numbered 0°. A bright light held close to a skele- 

 ton sphere in a position corresponding to P, would cast a 

 shadow of the parallels and meridians upon a tangent plane 

 corresponding exactly with the lines shown in figure 2. If 

 figure 2 is viewed with one eye through a short cylinder made 

 by rolling up a sheet of paper, or through, as it were, a tube 

 formed by doubling up the hand, the lines of the drawing will 



