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Thomas Jefferson’s Calculations of Latitude of Poplar Forest, 6 August–10 December 1815

Calculations of Latitude of Poplar Forest

1815 observns not all1 carefully made. the good & satisfactory are marked with an *

Aug. 30.  °  ′    Sep. 1.  °    Sep. 2. *  °  ′  ″
observed altitude 123– 46   122– 21   121– 35–  0
error of instrument    5      5      5  
123– 41   122– 16   121– 30–  0
true observed altitude  61– 50– 30  61–  8–  0  60– 45–  0
− refraction 31″ + paral. 3″     28     28     29
true altitude of ☉’s center:  61– 50–  2  61–  7– 32  60– 44– 31
 90–    90–  0–  0  90–
☉’s true Zenith distance  28–  9– 58    28– 52– 282    29– 15– 29
☉’s declinn at Greenw. 9°–15′     8– 31– 51      8– 10–  3 
 Pop. For. —     −  5    9– 10    −  4– 55   8– 26– 56    4– 56   8–  5–  7
Lat. Pop. For  37– 19– 58  37– 19– 243  37– 21– 36
  corrected to error instrum.  37– 18– 13   37– 17– 39  37– 19– 51
     Sep. 3 *      Sep. 6 *      Sep. 7. *      Sep. 15. *    
observed altitude 1  120– 51–  0 118– 36–  0 117– 55–  0 111°– 50–  0
− error of instrument 2    1– 30    1– 30    1– 30    1– 30
  120– 49– 30 118– 34– 30 117– 53– 30 111– 48– 30
true observed altitude 3  60– 24– 45  59– 17– 15  58– 56– 45  55– 54– 15
− refraction + parallax 4     29     29     30     34
true altitude of ☉’s center 5  60– 24– 16  59– 16– 46  58– 56– 15  55– 53– 41
 
☉’s declinn Greenwich 6   7–48– 8     6– 41– 37     6– 19– 13     3– 16– 49
− Pop. Forest 7  − 4–57   7– 43– 11    5–  1   6– 36– 36    5–  2   6– 14– 11    5–  8   3– 11– 41
true height Equator at P.F 8  52– 41–  5  52– 40– 10  52– 42–  4  52– 42–  0
   90      90–      90–      90–    
Zenith distance of equator4 = Lat. P.F. 9.  37– 18– 55  37– 19– 50  37– 17– 56  37– 18–  0
   Sep. 16.    Sep. 24    Sep. 25.    Oct. 4.    Nov. 13  
 1.   111°–  3′–  0   104°–50′– 0   104°– 2′– 0    74°– 55′– 0    69°– 37′–  0
 2. −    1– 30       
  111–  1– 30
 3.  55– 30– 45
 4. − +      35
 5.  55– 30– 10
 6.   2– 53– 42  
 7.    −  5 –  8   2– 48– 34
 8.  52– 41– 36
   90    
 9  37– 18– 24
   Nov. 14.  69–  4–  0  17.    21    23    Dec. 2.  
             67–33– 0    65–42– 0    64–45– 0    61–27– 0
         
   Dec 10                      
     59– 33–  0                
 

1815. Aug. 6. the average of 14. satisfactory observns makes the error of the instrument 1′½ to be deducted from altitude

MS (MHi); filed with TJ’s Weather Memorandum Book, 1802–16; with TJ’s Calculations of Latitude of the Sharp Peak of Otter and Natural Bridge, 18 Sept.–10 Nov. 1815, on verso; written entirely in TJ’s hand on recto of a single sheet of paper, with text through the end of the 2 Sept. entry perpendicular to remainder of text.

1. Word interlined.

2. Calculation to this point for September 1 reworked by TJ to correct error of subtracting 28′ from 61°–08′, rather than 28″; with duplicate uncanceled figures for refraction plus parallax and for the true altitude of the sun’s center editorially omitted.

3. Number inserted by TJ in place of “37–46–56.”

4. Preceding two words interlined.

Index Entries

  • astronomy; and calculations of Poplar Forest’s latitude search
  • geography; and TJ’s calculations of latitude search
  • Jefferson, Thomas; Writings; Calculations of Latitude of Poplar Forest search
  • latitude; calculations for Poplar Forest search
  • Poplar Forest (TJ’s Bedford Co. estate); latitude of search
  • sun; and calculation of latitude search

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Source Project
Jefferson Papers
Title
Thomas Jefferson’s Calculations of Latitude of Poplar Forest, 6 August–10 December 1815
Author
Jefferson, Thomas
Date
August–December 1815

Reference

Cite as
“Thomas Jefferson’s Calculations of Latitude of Poplar Forest, 6 August–10 December 1815,” Founders Online, National Archives, https://founders.archives.gov/documents/Jefferson/03-09-02-0153. [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. 245–247.]