Thomas Jefferson Papers
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Thomas Jefferson’s Calculations of Latitude of Willis’s Mountain, 8-9 December 1816

Calculations of Latitude of Willis’s Mountain

Willis’s mountain. Long. W. from Greenwich. 78°–49′–31″

observations with Borda’s circle.

Dec. 8. 1816     Dec. 9. 1816.  
  °  ′   ″ 
1816. Dec. 8.  ½ observed alt. ⊙ 29–49–30   29–44–30
−  error of instrumt 1–11 ½   1–11 ½
 
true observd alt. 29–48–18 ½   29–43–18 ½
−  refractn + parallax 1–30     1–30  
true Altitude of ⊙ 29–46–48   29–41–48
decln Greenwich  22–45–51      22–51–51
more for 79° W. 1–15  22–47– 6     22–53– 6   1–15
true height of Æquator 52–33–54   52–34–54
90–        90   
Zenith dist. = lat. 37–26– 6   37–25– 6

note the observn of Dec. 9. was compleatly perfect & satisfactory.

MS (MHi); filed with TJ’s Weather Memorandum Book, 1802–16; written entirely in TJ’s hand on verso of his Calculations of Latitude of Poplar Forest, 8 Nov.–3 Dec. 1816.

On a separate, narrow sheet, TJ recorded his key finding on these days:

“observns with Borda W’s. Mount.

1816. ° ′
Dec. 8. mer. alt. ⊙ 59– 39/ 29
9 59– 29½
note this last was a most perfect observn. the 1st not perfect” (MS in MHi; filed with TJ’s Weather Memorandum Book, 1802–16; entirely in TJ’s hand, with his related calculations of instrument error for his Borda’s circle, headed “1816. Nov. Dec. error of Borda,” on verso).

Index Entries

  • astronomy; and calculations of Willis’s Mountain’s latitude search
  • Borda, Jean Charles de; and surveying instruments search
  • Borda’s circle (surveying instrument) search
  • geography; and TJ’s calculations of latitude search
  • Greenwich Observatory, England; and prime meridian search
  • Jefferson, Thomas; Writings; Calculations of Latitude of Willis’s Mountain search
  • latitude; calculations for Willis’s Mountain search
  • sun; and calculation of latitude search
  • surveying; and J. C. Borda’s circle search
  • Willis’s Mountain; TJ takes latitude of search

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Source Project
Jefferson Papers
Title
Thomas Jefferson’s Calculations of Latitude of Willis’s Mountain, 8-9 December 1816
Author
Jefferson, Thomas
Date
8 December 1816

Reference

Cite as
“Thomas Jefferson’s Calculations of Latitude of Willis’s Mountain, 8-9 December 1816,” Founders Online, National Archives, https://founders.archives.gov/documents/Jefferson/03-10-02-0434. [Original source: The Papers of Thomas Jefferson, Retirement Series, vol. 10, May 1816 to 18 January 1817, ed. J. Jefferson Looney. Princeton: Princeton University Press, 2013, pp. 571–572.]