“An Unusual Rainbow”

Abstract

I READ with interest a letter with the above heading in NATURE (vol. xxxvi. p. 581) from Mr. S. A. Hill of Allahabad, India, of date September 18, 1887. He describes a brilliant rainbow which he saw after the sun had set, and states that such a phenomenon “must be of rare occurrence,” and that he had “never before seen anything similar, nor read anywhere a description of a rainbow after sunset.” I had not read his letter when, on the evening of the 1st inst. I observed a similar rainbow. I saw it first at 7h. 25m. p.m., the registered time of sunset here for that day. It lasted for nearly fifteen minutes. The western horizon was cloudy, and the sunset a fine one. The bow was exceedingly brilliant, and as far as I could judge, a perfect semicircle, the ends of the arc being about 4° above the horizon. There was a secondary bow equally perfect, and of remarkable brightness; the brilliant glow below the primary, and the marked dulness between it and the secondary, added to the beauty of the sight. After reading Mr. Hill's letter, I published my observations in a letter to the Argus, that others might confirm or correct them. I have received six replies, all in accord with my observations. One of my correspondents informed me that he had, some years ago, seen a lunar rainbow formed just before the moon had risen.