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 152
the beam proceeded in a straight linetowards T, where it formed a round white spot;but being now bent out of its course by the prism,it formed an oblong image OP, upon the whitepasteboard, or screen LM, containing the sevencolours marked in the figure—the red being theleast, and the violet the most… … degrees, and the distance of the pasteboard fromthe prism about 18 feet, the length of the imageOP will be about 10 inches, and the breadth 2inches. The sides of the spectrum are rightlines distinctly bounded, and the ends are semi-circular. From this circumstance it is evidentthat it is still the…
Astronomy · Astronomical instruments · Telescopes
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