Elements of natural philosophy (Volume 2-3) . ich is 50° 57 — 42° 02 = 8° solar disk being about 32, the width of both bowsmust be increased by this quantity, the solution havingbeen made upon the supposition that the light flows froma point. The primary is, therefore, 2° 17 in width, andthe secondary 3° 42. The half of 32 being added tothe radius of the red in the primary, will give 42° 18,hence, if the sun be more than that height above thehorizon, this bow cannot be seen. When higher than54° 23, no part of the secondary will be find elements By substituting in Equation (10
Elements of natural philosophy (Volume 2-3) . ich is 50° 57 — 42° 02 = 8° solar disk being about 32, the width of both bowsmust be increased by this quantity, the solution havingbeen made upon the supposition that the light flows froma point. The primary is, therefore, 2° 17 in width, andthe secondary 3° 42. The half of 32 being added tothe radius of the red in the primary, will give 42° 18,hence, if the sun be more than that height above thehorizon, this bow cannot be seen. When higher than54° 23, no part of the secondary will be find elements By substituting in Equation (106), 3 for n, we mightof a tertiary bow; £n(j the radii of a third bow, which would be found toencircle the sun at the distance of about 43° 50; but theproximity of the sun, together with the great loss oflight arising from so many reflexions, renders this bowso faint as to produce no impression ; it is, therefore,never seen. When thosebows will beinvisible; Tertiary notseen. Fisr. 80. Illustration forthe primary andsecondary bows;. 6- a maximum § 127. By means of the calculus it is easily shownandJininmm7 ^at ^ *n Equation (104), is a maximum for the primaryforth:secondary; and a minimum for the secondary. This explains the ELEMENTS OF OPTICS. 321 remarkable fact that the space between these bows always Eemarkabl0 x d appearance of appears darker than any other part of the heavens in the the heavensvicinity of the bow ; for, no light twice refracted and once !jetween thes* ° bows accounted reflected can reach the eye till the drops arrive at the prim- , and none which is twice refracted and twice reflected,can arrive at the eye after the drops pass the secondary ;hence, while the drops are descending in the space be-tween the bows, the light twice refracted with one or twointermediate reflexions, will pass, the first above, and thesecond below or in front of the observer. The same discussion will, of course, apply to the lunarrainbow which is sometimes seen.
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