## An Elementary Treatise on Optics: Intented Chiefly to Elucidate the Principles of the Construction of Telescopes, and Some Other Optical Instruments |

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achromatic angle of incidence angle subtended aperture axes centre centrical pencil chromatic dispersion circle of aberration circle of least colours concave lens cones converging pencil convex lens corresponding deviation diameter diaphragm diminishes direct pencil dispersive powers distinct vision diverging pencil emergent pencil emergent rays equal equation excentrical pencil eye-glass focal length foci focus of rays formed formula given glass greater Hence incident pencil incident ray index of refraction infinite distance intersection last article least circle least confusion lenses less medium mirror nearly negative object object-glass parallel rays passing pencil of rays perpendicular placed plane surface point Q position primary plane prime conjugate prism quantity radiant radius ratio ray of light reflexion refracted ray refracting angle refractive indices retina right angles secondary plane sphere spherical aberration substituting supposed telescope transmitted vertex violet