A Treatise on Optics

aberration achromatism angle of incidence axis QA bright centre circle of least cloth coincides colours concave conical surfaces converge convex lens cos² Crown 8vo cuts the axis determine deviation direct pencil distance emergent equation eye-glass eye-piece Fcap fixed lines focal length geometrical focus Hence illumination image formed incident directly incident pencil index of refraction intersection lenses luminous point magnifying power medium mirror object object-glass parallel rays passes pencil of light pencil of parallel pencil of rays pencil whose axis perpendicular plane surface point of incidence point Q position primary plane principal focus principal plane prism radii radius rays incident reflected or refracted reflected pencil reflexion or refraction refracted rays refracting angle refracting surface refractive index shew small pencil spectrum sphere spherical reflector spherical surface supposed telescope thin lens v₁ v₂ αμ