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 381
and B. The focus ofthe telescope is adjusted by a screw, the threads ofwhich are formed upon the outside of a tube intowhich the eye-piece slides. The eye-piece andapparatus connected with it, is screwed into theinside of the main tube, when not in use, whenthe instrument forms a compact brass…
Astronomy · Astronomical instruments · Telescopes
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