## 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 axis centre centrical pencil chromatic dispersion circle of aberration circle of least coloured concave lens cones converging pencil convex lens cosē deviation diameter diaphragm diminishes direct pencil dispersive powers emergent pencil equal equation excentrical pencil eye-glass eye-piece focal length foci formed formula glass greater Hence incident pencil incident ray infinite distance intersection last article least circle least confusion lenses luminous point magnifying power medium mirror nearly object object-glass object-speculum parallel rays passing pencil of rays perpendicular placed plane surface point Q primary plane prime conjugate prism quantity radiant radius ratio ray of light rays reflected reflected pencil reflected rays reflexion refracting angle refractive indices retina right angles secondary plane similar triangles sphere spherical aberration supposed telescope vertex violet