* 
186 Trans. Acad. Sci. of St. Louis. 
cone through the point where the second arc meets the ele- 
FIGURE 2. 
.ment of the cone intersects the first arc at a point A, inside 
the cone. 
Then, from the figure, 
‘CP = GE cose =-¢ cosa 
CP = CO cos ECK = cos ECK 
= cos (a — DCR) 
