## An Elementary Treatise on Optics: Containing the higher propositions, with their applications to the more perfect forms of instruments, Part 2 |

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achromatic achromatic lens angle of incidence aperture approximate focus approximate value axis caustic chromatic dispersion circle of confusion cloth coefficient concave conjugate foci convex lens convexo-plane curvature direct pencil distance diverging pencil Edition ellipse equal equation excentrical pencils expression eye-glass eye-piece falling obliquely field-glass find the form focal length focal line gives incidence and emergence incident pencil latus rectum least circle lenses Let Q light luminous point meniscus microscope nearly negative object object-glass oblique aberration oblique pencil optical parabolic parallel incident rays parallel rays pencil is incident pencil passes perpendicular plane plano-convex PM=y primary and secondary prism Prop proposition quantity radius ray refracted reflected reflexion refracted pencil refracted rays refracting surface refractive index second approximation second surface secondary foci shews small pencil small term spherical mirror Substituting the values telescope thin lens tion triangles virtual image