146 Trans. Acad. Sci. of St. Louis. 



focus, F. If we now let 



<p = ^BFC, we have -—^ — j^—, = tan (p 



{a^ — b^y- ^ 



Through the center of the ellipse draw OD parallel to BF; 

 then 



DH = ? tan <p. 



I 



Figure 5. 

 Through D draw Z)^ perpendicular to CD; then 



HK = DH ' tan (p = $ tan^ (p = 



a'^-b^ 



I; (22) 



therefore, (eq. 21) the line through K parallel to the axis of 

 Y id this asymptote. 



To find the asymptote parallel to the axis of X, through 

 the point P drawP^ perpendicular to BF; then 



QH = 7) tan (p. 



