RAINBOW,. See Meteorology and Optics.

Lunar RainBow. The moon sometimes exhibits the phenomenon of an iris or rainbow by the refraction of her rays in drops of rain during the night-time. But this phenomenon is very rare. In the Philosophical Transactions for 1783, however, we have an account of three which were seen in one year, and all in the same place; it is communicated in two letters by Mr Marmaduke Tunstall. The first was seen on the 27th of February 1782, at Greta Bridge, Yorkshire, between seven and eight at night, and appeared in tolerably distinct colours, similar to a solar one, but more feint, the orange colour seeming to predominate. It happened at full moon, at which time alone they are said to be always seen. Though Aristotle is stated to have observed two, and some others have been seen by Snellius, Mr Tun-stall could only find two described with any accuracy; one by Plot, in his History of Oxfordshire, which was seen by him in 1675, though without colours; and the other seen by a Derbyshire gentleman at Glapwell, near Chesterfield, described by Thoresby, and inserted in the Philosophical Transactions, No. 331. This was about Christmas 1710, and is said to have had all the colours of the iris Solaris. The night was windy; and although there was then a drizzling rain and a dark cloud, in which the rainbow was reflected, it proved afterwards a light frost.

Two others were afterwards seen by Mr Tunstall. One of these was observed on the 30th of July, about eleven o’clock, which lasted about a quarter of an hour, but without colours; and the other, which appeared on the 18th of October, was perhaps the most extraordinary one of the kind that had ever been seen. It became visible about nine o’clock, and con[7:19:61]tinued, though with very different degrees of brilliancy, till 'past two. At first, though a strongly-marked bow, it was without colours; but afterwards they were very conspicuous and vivid, in the same form as in the solar, though fainter, the red, green, and purple being the most distinguishable. About twelve it was the most splendid in appearance; its arc was a considerably smaller segment of a circle than a solar; and its south-east limb first began to fail, a considerable time before its final extinction. The wind was very high, nearly due west, accompanied most part of the time with a drizzling rain. It is a singular circumstance, that three of these phenomena should have been seen in so short a time and in one place; as they have been esteemed, ever since the time of Aristotle, who is said to have been the first observer of them, and saw only two in fifty years, and since by Plot and Thoresby, almost the only two English authors who have spoken of them, to be exceedingly rare. They evidently appear to be occasioned by a refraction in a cloud or turbid atmosphere, and in general are indications of stormy and rainy weather. Thoresby, indeed, says the one he observed was succeeded by several days of fine serene weather. One particular, rather singular, in the second, namely, that of July the 30th, was its being six days after the full moon; and the last, though of so long a duration, was three days before the full moon. That of the 27th of February was exactly at the full, which used to be judged the only time when they could be seen, though there is an account that Weidler observed one in 1719, during the first quarter of the moon, with faint colours, and in very calm weather.

In the Gentleman’s Magazine for August 1788 an account is given of a lunar rainbow by a correspondent, who saw it. “On Sunday evening the 17th of August,” says he, “after two days, on both of which, particularly the former, there had been a great deal of rain, together with lightning and thunder, just as the clocks were striking nine, twenty-three hours after full moon, looking through my window, 1 was struck with the appearance of something in the sky, which seemed like a rainbow. Having never seen a rainbow by night, I thought it a very extraordinary phenomenon, and hastened to a place where there were no buildings to obstruct my view of the hemisphere. Here I found that the phenomenon was no other than a lunar rainbow; the moon was truly ‘ walking in brightness,’ brilliant as she could be; not a cloud was to be seen near her; and over against her, toward the north-west, or perhaps rather more to the north, was a rainbow, a vast arch, perfect in all its parts, not interrupted or broken as rainbows frequently are, but Unremittedly visible from one horizon to the other. In order to give some idea of its extent, it is necessary to say, that as I stood toward the western extremity of the parish of Stoke-Newington, it seemed to take its rise from the west of Hampstead, and to end, perhaps, in the river Lea, the eastern boundary of Tottenham; its colour was white, cloudy, or grayish, but a part of its western leg seemed to exhibit tints of a faint sickly green. I continued viewing it for some time, till it began to rain; and at length the rain increasing and the sky growing more hazy, I returned home about a quarter or twenty minutes past nine, and in ten minutes came out again; but by that time all was over, the moon was darkened by clouds, and the rainbow of course vanished.”