The practical astronomer : comprising illustrations of light and colours, practical descriptions of all kinds of telescopes, the use of the equatorial-transit, circular, and other astronomical instruments, a particular account of the Earl of Rosse's large telescopes, and other topics connected with astronomy (1845)
Dick, Thomas, 1774-1857 · London : Seeley, Burnside, and Seeley · leaf 369
lenses ; andthis may be done both in the negative and thepositive eye-pieces; but as the distance betweenthe two lenses is necessarily considerable, to makeroom for the diagonal position of the reflector, themagnifying power cannot be great; otherwise, adiagonal eye-piece of this construction… … In fig. 77, AB represents the plano-convex lensnext the object, which is about 2 inches in focallength, and f inch in diameter; CD, a plainmetallic speculum of an oval form, well polished,and placed at half a right angle to the axis of thetube; and EF another plano-convex lens, about\\ inch focal…
Astronomy · Astronomical instruments · Telescopes
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