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Thomas Jefferson’s Calculations of Latitudes of the Sharp Peak of Otter and Natural Bridge, 18 September–10 November 1815

Calculations of Latitudes of the Sharp Peak of Otter and Natural Bridge

1815. Sep. 18. Sharp peak of Otter		°		′		″	1815. Sep. 20. Natural bridge.	°		′		″
Observed altitude of ⊙.		109	–	21	–	0		107	–	29	–	0
− error of instrument				1	–	30				1	–	30
		109	–	19	–	30		107	–	27	–	30
true observed altitude		54	–	39	–	45		53	–	43	–	45
− refractn 41″ + parallax 4″						37	− 42″ + 4″1					38
true altitude of ⊙’s center		54	–	39	–	8		53	–	43	–	7
− ⊙’s decln Greenwich	2–7–17						1°–20′– 42″
for 79°–45′–57.″ W	5– 8	2	–	12	–	25	5 – 9	1	–	25	–	51
true height of Æq.2 at Peak		52	–	26	–	43		52	–	17	–	16
		90	–					90
Zenith distance of Æq. at Peak		37	–	33	–	173		37	–	42	–	44
1815. Nov. 10. Sharp peak of Otter		°		′		″
Observed altitude		71	–	8	–	0
− error of instrument				1	–	30
corrected observn		71	–	6	–	30
true observed altitude		35	–	33	–	15
− refractn 1′–19″ + parallax 7″=		−		1	–	12
true Alt. of ⊙’s center		35	–	32	–	3
⊙’s decln Greenwich	17°–0′– 1″
for 79°–45′–57.″ W. +	3 –33	17	–	3	–	33
height of Æq. at Peak		52	–	35	–	36
		90	–
Zenith dist. or Lat.		37	–	24	–	24
observn of Sep. 18.		37	–	33	–	17
		74	–	57	–	41
mean of 2. observations		37	–	28	–	50

MS (MHi); filed with TJ’s Weather Memorandum Book, 1802–16; on verso of TJ’s Calculations of Latitude of Poplar Forest, 6 Aug.–10 Dec. 1815 (printed at the latter date); entirely in TJ’s hand. Dft (CSmH: JF); on verso of TJ’s Notes on Distances between Poplar Forest and Natural Bridge, [ca. 17–21 Sept. 1815], and TJ’s MS pocket notes for his MB description begins James A. Bear Jr. and Lucia C. Stanton, eds., Jefferson’s Memorandum Books: Accounts, with Legal Records and Miscellany, 1767–1826, 1997, The Papers of Thomas Jefferson, Second Series description ends entries covering 17–21 Sept. 1815; entirely in TJ’s hand; lacking calculations for 10 Nov. and textual explanation of calculations for 18 and 20 Sept.

TJ also created, but never used, a sheet with four additional blank versions of the chart employed here, two each on recto and verso (MS in MHi; filed with TJ’s Weather Memorandum Book, 1802–16; entirely in TJ’s hand; dated Sept. 1815).

TJ confirmed elsewhere that he observed the latitudes of the Sharp Peak of Otter and of Natural Bridge as 37°–33′–17″ and 37°–42′–44″ on sep. 18 and sep. 20, respectively (MB description begins James A. Bear Jr. and Lucia C. Stanton, eds., Jefferson’s Memorandum Books: Accounts, with Legal Records and Miscellany, 1767–1826, 1997, The Papers of Thomas Jefferson, Second Series description ends , 2:1313, 1314). He also noted in a handwritten revision to the query on mountains in his Notes on the State of Virginia, composed sometime after November 1815, that “Two observns with an excellent pocket sextant gave a mean of 37°–28′–50″ for the Lat. of the sharp Peak of Otter” (Jefferson, Notes on the State of Virginia [London, 1787; Sowerby, description begins E. Millicent Sowerby, comp., Catalogue of the Library of Thomas Jefferson, 1952–59, 5 vols. description ends no. 4167; Poor, Jefferson’s Library description begins Nathaniel P. Poor, Catalogue. President Jefferson’s Library, 1829 description ends , 7 (no. 365); TJ’s copy with revisions in ViU, including this one tipped in between pp. 28 and 29]).

1. Equation not in Dft.

2. Abbreviation for “Equator,” here and below.

3. In Dft TJ canceled a preliminary version of his 18 Sept. calculation and replaced it with one that corrected a subtraction error in the first step.

Index Entries

astronomy; and solar observations search
Jefferson, Thomas; Writings; Calculations of Latitudes of the Sharp Peak of Otter and Natural Bridge search
Jefferson, Thomas; Writings; Notes on the State of Virginia search
latitude; calculations for Natural Bridge search
latitude; calculations for Peaks of Otter search
Natural Bridge, Va.; calculations of latitude search
Notes on the State of Virginia (Thomas Jefferson); TJ’s revisions to search
Peaks of Otter, Va.; latitude of search
scientific instruments; sextants search
sextant; TJ uses search
sun; and calculation of latitude search

You Are Looking At

Source Project: Jefferson Papers
Title: Thomas Jefferson’s Calculations of Latitudes of the Sharp Peak of Otter and Natural Bridge, 18 September–10 November 1815
Author: Jefferson, Thomas
Date: 18 September 1815

Reference

Cite as: “Thomas Jefferson’s Calculations of Latitudes of the Sharp Peak of Otter and Natural Bridge, 18 September–10 November 1815,” Founders Online, National Archives, https://founders.archives.gov/documents/Jefferson/03-09-02-0021. [Original source: The Papers of Thomas Jefferson, Retirement Series, vol. 9, September 1815 to April 1816, ed. J. Jefferson Looney. Princeton: Princeton University Press, 2012, pp. 36–37.]