Astronomy, a handy manual for students and others (1918)
Dyson, Frank Watson, Sir, 1868-1939 · New York, E.P. Dutton & Co. · leaf 78
has three import-ant properties— (i) It increases the amount of light which entersthe eye from a star, and thus enables fainter stars tobe seen. (2) It magnifies the apparent angle between twostars, and thus greater accuracy can be obtained inangular measurements. (3) It obviates the necessity for… … 68 ASTRONOMY the focus of the lens. At F a bright point is formed,called the image of the star. If the rays which passthrough F be intercepted by a second lens L, they canbe again converted into a parallel beam of light. Ifthe diameter of the second beam is no wider than thepupil of the eye, all…
Astronomy
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