On the Cross Ratio of Four Point Groups of an Involution

The set of point-groups which are ischolar_mains of polynomials of the form, f(x) - λΦ(x), [where f(x), Φ(x) are of order n, and λ is an arbitrary parameter], is often called a generalised involution of order n. An examination of the cross ratio of four point-groups of a generalised involution, will reveal the principle upon which depends the expression given by Mr. R. Gopalaswamy (J. I. M. S., Dec 1922: 'Pencils of Conics') for the cross ratio of four conics of a pencil-or, what is the same thing, of four point-pairs of an Involution of order 2.