m 



KANSAS UNIVERSITY QUARTERLY. 



determine </i. If ^ is tangent to K, (j\ will be tangent to K\ and the 

 two points of contact will be collinear with S. If the given line g 

 passes through S and cuts K in P and K\ in P\, the corresponding line 

 is found by joining P\ to S\ the point where the tangent to A" at S 

 cuts Ki. 



Theorem 1. ^i collineation or projective transformation of the 

 plane can he completely constructed hy means of two conies K and 

 K\ intersecting in S. 



3. Invariant Points and Lines. The conies /rand lu intersect 

 in S and generally in three other points A, B, C. Since any line 



