Brewster, David, Sir, 1781-1868, Bache, A. D. (Alexander Dallas), 1806-1867 · Philadelphia : Lea and Blanchard · leaf 298
reflecting telescopes to refracting ies:— Focal lengths in feet. Aperture in InehM. MagnifyinR powers. Price ingu 1 30 35 to 100 14 2 4-5 90 300 35 3 6-3 100 400 75 4 7-6 120 500 100 7 12-2 200 800 300 12 18-0 300 1200 800 Cassegrainian Telescope. (209.) The Cassegrainian telescope, proposed by M.… … of the object M N, and an image of M N will be formed atm n between E and F as in the Gregorian instrument. Theadvantage of this form is, that the telescope is shorter thanthe Gregorian by more than twice the focal length of thesmall speculum; and it is generally admitted that it^givesmore light,…
Optics
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