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