Extract of a Letter from J. Franklin, Esq. Relative to a Luminous Arch. Communicated by Sir Joseph Banks, Bart. P. R. S.

VI. Extract of a Letter from J. Franklin, Esq. relative to a luminous Arch. Communicated by Sir Joseph Banks, Bart. P. R. S. Read December 14, 1786. Blockley, Feb. 25, 1786. I CANNOT help giving you a line to let you know, that I observed a very odd appearance in the heavens on Monday evening last, about a quarter before nine o'clock. Happening to go out of the house, I was very much surprized to see a white light, broader than a rainbow, pass across the heavens from east to west. At first I thought it might be a lunar rainbow; but, after some moments reflection, I knew it could not be from its situation. I now began to observe its situation and form more minutely. It was a bright white light, about 5 degrees wide in the zenith, and gradually coming to a point both ways. The eastern point terminated between Arcturus and the bright star in the knee of Bootes. The western point came nearly to the star marked a in the Whale's mouth. The southern side of the light was about 5 degrees above Castor, passing eastward above Berenice's hair, and westward near Aldebaran, and through the Hyades. I observed it till nine o'clock. Aldebaran was south of it when I first saw it; but it passed, and got north, before nine o'clock. At five minutes past nine, no more of it was to be seen. It gradually went off in a few minutes. The sky was very clear from clouds, and the stars shone bright,