Let Fig. 47a, Plate X., represent a spherical reflector of semi-aperture
C. . Ej or C . . Eg = -4. Let Q . . Q' be a finitely distant flat object per-
pendicular to the axis C . . Q. Let be the centre of curvature, the



radius being . . C = ?\



Primary Plane



We will deal with rays in the primary plane first.
