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 233
I 208 THE PRACTICAL ASTRONOMER. is seen under the small angle FED. B will re-present its apparent magnitude at 4^ yards distantunder the angle HEG, and the circle C, its appa-rent magnitude at 3 yards distant, under the largeangle KEI. This may be otherwise illustrated by the fol-lowing figure. Let… … viewed directly by the eye QR. From each ex-tremity A and B draw the lines AN,BM, intersect-ing each other in the crystalline humour in I:then is AIB the optical angle which is the measureof the apparent magnitude or length of the objectAB. From an inspection of this figure, it willevidently appear…
Astronomy · Astronomical instruments · Telescopes
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