Astronomy, a handy manual for students and others (1918)
Dyson, Frank Watson, Sir, 1868-1939 · New York, E.P. Dutton & Co. · leaf 83
an opticians, Alvan Clark & Sons. Reflecting Telescope.—In 1668 Newton made a smallreflecting telescope which magnified thirty times. Inthis instrument the light from a star falls on a concavemirror of speculum metal—an alloy of copper andtin approximately in the proportions of four atoms… … Diag. XXXIX. 72 ASTRONOMY the tube, this image is shifted to the side of the tele-scope, where it can be viewed by an eye-piece (Dia-gram XXXIX). In1723 Hadley, the in-ventor of the sextant,made a reflector with amirror of 5J inches anda focal length of 62inches with which a magnification of 200…
Astronomy
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