A Treatise on Optics

aberration achromatic angle of incidence angular aperture axis breadth bright caustic centre coincides colours concave converge convex lens cos² curve diameter direct pencil distance edge emergent equal equation excentrical eye-glass eye-piece field of view focal length foci geometrical focus glass Gregorian telescope Hence illumination image formed inches incident pencil index of refraction intersection latus rectum lenses luminous point magnifying power medium object object-glass parabola parallel rays passing pencil of light pencil of parallel pencil of rays placed plane mirror plane surface point of incidence position principal focus principal plane prism radii radius ray of light rays incident reflected or refracted reflected rays reflector refracted pencil refracted rays refracting angle refracting surface refractive index shew sin² small pencil spectrum sphere spherical reflector spherical surface subtends supposed v₁ αμ