William Dunbar to the American Philosophical Society, via Thomas Jefferson, read January 16, 1801
Transactions of the American Philosophical Society, Vol. IV. Philadelphia, 1804.
This letter, with several other missives and reports written by Dunbar, were forwarded by Jefferson to the American Philosphical Society, where they were read before the Society and later published in the Transactions of the Philosophical Society of America in 1804. Dunbar provides detailed notes on the climate in and near Natchez.
TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY
No. II METEOROLOGICAL OBSERVATIONS, FOR ONE ENTIRE YEAR.
MADE by William Dunbar, Esq. at the Forest four and & half miles east of the river Mississippi Maps: John Mitchell (1755) Antoine-Simon Le Page du Pratz (1763) Thomas Hutchins (1778) Aaron Arrowsmith (1811) Aaron Arrowsmith (1802) in North Lat. 31° 28' and Long. 91° 30' West of Greenwich, on an eminence about 150 feet higher than the level of the highest waters of the annual inundation of the Mississippi Maps: John Mitchell (1755) Antoine-Simon Le Page du Pratz (1763) Thomas Hutchins (1778) Aaron Arrowsmith (1811) Aaron Arrowsmith (1802) ; beginning on the 1st day of February 1799, and ending the 31st January 1800, inclusive. Communicated by Thomas Jefferson, President of the Society. Read 16th January, 1801:
IN the following observations, the strength of the wind is divided into four degrees, viz. No. 1. indicates a light Zephyr. No. 2. a brisk breeze. No. 3. a very strong wind. No. 4. a tempest or hurricane. When the course of the wind is noted, but the strength omitted, it is to be understood that the direction of the wind has been observed by the gentle movement of the clouds, or, perhaps, by the progress of smoke, while to the senses a perfect calm reigns below. When two currents of air have been observed, they are noted, the strength referring always to the latter current.
A mercurial thermometer of the best kind made in London, with Farhenheit's scale adapted, consisting of divisions of one line to the degree, was suspended to the inner part of a column of the northern gallery of a large dwelling house nine feet from the earth, in such a manner that the thermometer was not in contact with the column, being twelve feet distant from the wall of the building, and entirely defended from the sun-beams by surrounding forest trees, while a free circulation of the atmosphere prevailed below. Frequent experiments shewed that during the hot hours of a summer's day, the thermometer being removed into a hail within the building and suspended twelve feet from the wall, the mercury fell from two to two and a half degrees, although a free circulation was maintained by two large open windows and one door in each of the opposite walls of the building.
It may be proper to remark further that the summer of 1799 was accounted cool, the thermometer never having risen above 92° whereas during the warm season of 1800 it was often at 96° and 97° though at the same time if the thermometer was placed under a deep shade of surrounding trees, it would fall to 91°. It appears that the proper situation for the thermometer, is such as is completely shaded from the direct sun-beams, but not so as to exclude all influence by reflection from the surface of the earth, being that which will best indicate the influence of atmospheric heat upon vegetation, which is what has been attempted to be shewn in the following journal.
NOTE. The Society have been induced to publish this journal entire, as it is certainly the first that has been kept with so much accuracy and attention in that part of the world, and may serve as a standard with which to compare future observations.
[Ed. note: The subsequent pages of this report consist of detailed tables of meteorological observations. Please view their images.]