RC (DLC); at foot of text: “Thomas Jefferson Esqr”; endorsed by TJ as received 5 Sep. and so recorded in SJL. Enclosure: Extracts of correspondence from William Dunbar, the first one describing “a Curious phenomenon” in the form of a semicircular rainbow of at least three rings observed just after sunset; he surmises that the visual effect is due to horizontal refraction such as has been described in the Transactions of the Royal Society as occurring in the English Channel and on the coasts of England and France; in the second extract, Dunbar observes that according to newspaper reports the first week of May was unusually cold in Philadelphia and New York, and his record of meteorological observations indicates that the weather was colder than expected at Natchez that week also; he includes figures comparing temperature, barometric pressure, and weather conditions at Natchez and Philadelphia during part of May (Tr entirely in Vaughan’s hand, undated, subjoined to letter beginning on verso of RC); Vaughan conveyed Dunbar’s description of the rainbow to the American Philosophical Society in a meeting on 19 Aug. (APS description begins American Philosophical Society description ends , Proceedings, 22, pt. 3 [1884], 340). Other enclosure not found.