Dear Sir James,

I Send under cover the representation of a very singular Halo of the Moon, (See Pl. V,), seen here on the night of the 18th of February last, about 10 o'clock, and this I have hitherto delayed, in order, if possible, to gain farther information in the neighbourhood concerning it.

During the short continuance of the small halo, which did not exceed 10 minutes after I got notice of it, I could not lay my hands on any other instrument to take the angles, but a Sisson's theodolite, which, unluckily, having been constructed so as not to admit of a vertical angle so great as the moon's altitude then was, I laid it aside, not recollecting that it might have measured several of the smaller angles. But I observed sundry marks, from which I took the angles as exactly as I could next day.