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 220
dto view the picture. The focal distances of thelenses used in large instruments of this kind, aregenerally from eight to twelve feet, in which casethey produce a telescopic effect upon distant objects, ON THE CAMERA OBSCURA. 195 so as to make them appear nearer than whenviewed with the naked eye.… … B this form. AC is a convex lens placed near theend of a tube or drawer, which is moveable in theside of a square box, within which is a planemirror DE, reclining backward in an angle offorty-five degrees from the perpendicular pn.The pencils of rays flowing from the object OB,and passing through…
Astronomy · Astronomical instruments · Telescopes
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