RC (PPAmP); dateline at foot of text; above salutation: “To Thomas Jefferson, Esquire”; notation in an unidentified hand: “Presented to the Amn Philosl Society Minutes 20. Oct. 1809 by Thomas Jefferson.” Enclosure: Treat, journal of Arkansas meteorological observations, 1 Oct. 1805–31 Dec. 1808, describing “Arkansa” as “situated on the left bank of the Arkansa river, which is about fortyfive feet above the lowest fall of its waters,” latitude 34° 21′ North, fifty miles by water and twenty miles in a direct line from the Mississippi, with generally level land “much diversified with Forests and open extensive Prairies,” much of which overflowed annually “to within four or five miles of the town”; stating that the observations were formed on the plan of William Dunbar in APS, Transactions, vol. 6, pt. 1, and that Treat’s instruments were “suspended, on the North side of a Gallery, about fifteen feet from the Ground, against the Wall of a log or Timber house, with open Grass plat in front”; and reporting thrice-daily readings of thermometer, barometer (until that instrument broke on 14 May 1807), wind direction and strength, rainfall, and state of the weather, as well as monthly general remarks and a yearly recapitulation giving monthly highs, lows, and mean values (MS in PPAmP, in Treat’s hand; Tr in DLC: TJ Papers, ser. 7, Weather Memorandum Book, at head of page followed by entry for 13 Dec. 1809, abstract in TJ’s hand, using Treat’s data to compile a table of monthly maximums, minimums, and means for thermometer readings, maximum and minimum barometer readings, amount of rain, and days of rain, with heading in TJ’s hand: “The Meteorological observations of mr Treat from Oct. 1. 1805. to Dec. 30. 1807 at the post on the Arkansa, about 20. miles in a direct line, above the mouth of the river, Lat. 34° 21′ reduced to an average for each month. the river is there 150 yards wide”). Letter and enclosure enclosed in TJ to Robert Patterson, 31 Aug. 1809.