The geography of the heavens : and class-book of astronomy : accompanied by a celestial atlas (1860)
Burritt, Elijah H. (Elijah Hinsdale), 1794-1838, Mattison, Hiram, 1811-1868 · New York : Mason Brothers · leaf 325
m the object on the right, and falling uponthe concave surface of the reflector at B, from which it is reflected back to a focus, andenters the eye of the observer at C. This telescope has no eye-piece. 103. The focal distance of a concave reflector is equal to halfthe radius of the sphere formed… … Here the curve of the speculum B is that of a circle, whose centeris 0; while the focus of the speculum is at D, which is only halfthe distance from B to C. 104. Reflecting telescopes are of several kinds—viz., the Gre-gorian, the Newtonian, the Cassegranian, the Herschelian, &c.The Gregorian…
Constellations · Stars
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