Thomas Jefferson Papers

# To Alden Partridge

Monticello Jan. 2. 16.1

Sir

I am but recently returned from my journey to the neighborhood of the Peaks of Otter, and find here your favors of Nov. 23 & Dec. 9. I have therefore to thank you for your meteorological table and the Corrections, of Colo Williams’s altitudes of the mountains of Virginia which I had not before seen; but especially for the very able extract on Barometrical measures. the precision of the calculations, and soundness of the principles on which they are founded furnish, I am satisfied, a great approximation towards truth, and raise that method of estimating heights to a considerable degree of rivalship with the trigonometrical. the last is not without some sources of inaccuracy, as you have truly stated. the admeasurement of the base is liable to errors which can be rendered insensible only by such degrees of care as have been exhibited by the Mathematicians who have been employed in measuring degrees, on the surface of the earth. the measure of the angles, by the wonderful perfection to which the graduation of instruments has been brought by a Bird, a Ramsden, a Troughton, removes nearly all distrust from that operation; and we may add that the effect of refraction, rarely worth notice in short distances, admits of correction by2 well established laws. these sources of error once reduced to be insensible, their geometrical employment is certainty itself. no two men can differ on a principle of trigonometry. not so, as to the theories of Barometrical mensuration. on these have been great differences of opinion, and among characters of just celebrity.

Dr Halley reckoned 110 I. of mercury equal to 90.f. altitude of the atmosphere:

Derham thought it equal to something less than 90.f.

 Cassini’s tables to 24° of the Barometer allowed 676. toises of altitude; Mariote’s to the same 544. toises Scheuchzer’s to the same 559. toises

 the result was, the mean height of the Sharp peak above f ye surface of Otter R. 2946.5 of the flat peak 3103.5 the distance between the two summits 9507.73

their rhumb N. 33° 50′ E. the distance of the stations of observation from the points in the bases of the mountains vertically under their summits was the shortest 19002.2 f. the longest 24523.3 f. these mountains are computed to be visible to 15. counties of the state, without the advantage of counter-elevations, and to several more with that advantage. I must add that I have gone over my calculations but once, and nothing is more possible than the mistake of a figure, now and then, in calculating so many triangles, which may occasion some variation in the result. I mean therefore, when I have leisure, to go again over the whole. The ridge of mountains of which Monticello is one, is generally low. there is one in it however, called Peter’s mountain, considerably higher than the general ridge. this being within a dozen miles of me North Eastwardly, I think, in the spring of the year, to measure it by both processes, which may serve as another trial of the Logarithmic theory. should I do this you shall know the result. in the mean time accept assurances of my great respect & esteem

Th: Jefferson

(); addressed: “Capt A. Partridge Norwich Windsor county Vermont”; franked; postmarked Milton, 3 Jan. ().

Edmond halley published his findings on the relationship between the height of mercury and altitude in “A Discourse of the Rule of the Decrease of the Height of the Mercury in the Barometer, according as Places are elevated above the Surface of the Earth,” of London, Philosophical Transactions 16 (1686/92): 104–16. William derham found in his experiments that mercury in a barometer would drop 110 of an inch at an elevation of either 80 or 82 feet (“Part of a Letter of Mr. William Derham … Giving an Account of some Experiments about the Heighth of the Mercury in the Barometer, at Top and Bottom of the Monument,” Philosophical Transactions 20 [1698]: 2–4). For one version of the tables of Jacques Cassini, Edme Mariotte, and Johann J. Scheuchzer, see John G. Scheuchzer, “The Barometrical Method of measuring the Height of Mountains, with two new Tables shewing the Height of the Atmosphere at given Altitudes of Mercury,” Philosophical Transactions 35 (1727/28): 537–47. Thomas nettleton’s tables were published as “Observations concerning the Height of the Barometer, at different Elevations above the Surface of the Earth,” Philosophical Transactions 33 (1724/25): 308–12.

TJ obtained the rules of Pierre Bouguer and Jean André Deluc for estimating heights barometrically from the entry on barometers in the Dictionnaire de Physique (Paris, 1793; forming part of the Encyclopédie Méthodique [Paris, 1782–1832; description begins E. Millicent Sowerby, comp., Catalogue of the Library of Thomas Jefferson, 1952–59, 5 vols. description ends no. 4889]), and he copied his resulting notes into his Weather Memorandum Book, 1776–1821 (). Sir isaac newton discussed the relationship between height and air density in The Mathematical Principles of Natural Philosophy, trans. Andrew Motte (London, 1729; repr. London, 1803; description begins E. Millicent Sowerby, comp., Catalogue of the Library of Thomas Jefferson, 1952–59, 5 vols. description ends no. 3721), 2:57–60. Bouguer published his mensuration of the mountains of South America in La Figure de la Terre, Déterminée par les Observations de Messieurs Bouguer, & de la Condamine (Paris, 1749; description begins E. Millicent Sowerby, comp., Catalogue of the Library of Thomas Jefferson, 1952–59, 5 vols. description ends no. 3804).

lignes are equal to a twelfth of an inch ( description begins James A. H. Murray, J. A. Simpson, E. S. C. Weiner, and others, eds., The Oxford English Dictionary, 2d ed., 1989, 20 vols. description ends ). TJ’s 15 Sept. 1776 calculation that Monticello was 512.17 feet in height can be found in his Weather Memorandum Book, 1776–1821 (). In his Notes on the State of Virginia, TJ described Monticello’s summit as being 500.f in “perpendicular height above the river which washes its base” ( description begins Thomas Jefferson, Notes on the State of Virginia, ed. William Peden, 1955 description ends , 76). à peu près: “approximation.”

1Reworked from “15.”

2TJ here canceled “known laws.”

3TJ here canceled “peak.”

# Index Entries

• altitude; barometers used to calculate search
• altitude; calculations for Peaks of Otter search
• altitude; of Monticello search
• altitude; of Peter’s Mountain search
• barometers; altitude calculated with search
• Bird, John; scientific-instrument maker search
• Bouguer, Pierre; and barometric calculation of altitude search
• Bouguer, Pierre; La Figure de la Terre search
• Cassini, Jacques Dominique de; and barometric calculation of altitude search
• Davis, William; editsThe Mathematical Principles of Natural Philosophy (I. Newton; trans. A. Motte) search
• Deluc, Jean André; and barometric calculation of altitude search
• Derham, William; and barometric calculation of altitude search
• Dictionnaire de Physique search
• Encyclopédie Méthodique search
• Halley, Edmond; and barometric calculation of altitude search
• Jefferson, Thomas; Travels; to Peaks of Otter search
• Jefferson, Thomas; Writings; Notes on the State of Virginia search
• La Figure de la Terre (P. Bouguer) search
• Mariotte, Edme; and barometric calculation of altitude search
• mathematics; logarithms search
• mathematics; trigonometry search
• meteorological observations; by A. Partridge search
• Monticello (TJ’s estate); altitude of search
• Motte, Andrew; translatesThe Mathematical Principles of Natural Philosophy (I. Newton; ed. W. Davis) search
• Nettleton, Thomas; and barometric calculation of altitude search
• Newton, Sir Isaac; and barometric calculation of altitude search
• Newton, Sir Isaac; The Mathematical Principles of Natural Philosophy (ed. W. Davis; trans. A. Motte) search
• Notes on the State of Virginia (Thomas Jefferson); and altitude of Monticello search
• Partridge, Alden; and calculation of altitude search
• Partridge, Alden; letters to search
• Partridge, Alden; meteorological observations search
• Peaks of Otter, Va.; altitude of search
• Peaks of Otter, Va.; TJ visits search
• Peter’s Mountain (Southwest Mountains); altitude of search
• physics; barometric calculation of altitude search
• Ramsden, Jesse; scientific-instrument maker search
• Ramsden, Jesse; theodolite of search
• Royal Society of London; transactions of search
• Scheuchzer, Johann J.; and barometric calculation of altitude search
• scientific instruments; barometers search
• scientific instruments; theodolites search
• Southwest Mountains; altitude of search
• surveying; and chain search
• The Mathematical Principles of Natural Philosophy (I. Newton; ed. W. Davis; trans. A. Motte) search
• theodolite search
• Troughton, Mr.; scientific-instrument maker search
• Williams, Jonathan; and altitude calculations search