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 47
to the square of the distance from the lumi-nous body. Thus, a person at two feet distancefrom a candle, has only the fourth part of thelight he would have at one foot, at three feet dis-tance the ninth part, at four feet the sixteenthpart, at five feet the twenty fifth part, and so onfor other… … Figure 1. Suppose the light which flows from a pointA, and passes through a square hole B, is re-ceived upon a plane C, parallel to the plane ofthe hole—or, let the figure C be considered asthe shadow of the plane B. When the distanceof C is double of B, the length and breadth ofthe shadow C will…
Astronomy · Astronomical instruments · Telescopes
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