Thomas Jefferson Papers
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Thomas Jefferson’s Calculations of Latitude of Poplar Forest, 8 November–3 December 1816

Calculations of Latitude of Poplar Forest

Nov. 8. °  ′  ″ Nov. 9. °  ′  ″ Nov. 12. °  ′  ″ Nov. 13. °  ′  ″ Nov. 15.1 °  ′  ″
½  observed altitude of 36– 1–30 35–44– 0 34–55–30 34–37–452 34– 0– 6
− ½  error of instrument   1–11½    1–11½3   1–11½    1–11½    1–11½ 
true observed altitude 36– 0–18½ 35–42–48½ 34–54–18½ 34–36–33½ 33–58–54½
refraction + parallax   1–10½   1–11½   1–14½   1–15½   1–16½
true altitude of ’s center 35–59– 8 35–41–37 34–53– 4 34–35–18 33–57–38
’s declinn Greenwich  16–38–30   16–55–47   17–45–52   18– 1–57   18–33–11 
+ at Poplar Forest 79°–46′ 3–42 16–42–12 4– 5  16–59–52 3–26  17–49–18 3–22  18– 5–19 3–13  18–36–24
true height of Æq. at P.F. 52–41–20 52–41–29 52–42–22 52–40–37 52–34– 2
90– 90 90 90 90–
zen. dist. Æq. = Lat. of P.F. 37–18–40 37–18–31 37–17–38 37–19–23 37–25–58
Nov. 214 °  ′  ″ Nov 22 °  ′  ″ Nov. 23 °  ′  ″ Dec. 3 °  ′  ″ °  ′  ″
½  observed altitude of 32–39–30 32–30–30 32–15–45 30–35–155 Dec.  3.6  37–16–26
½  error of instrument   1–11½    1–11½    1–11½    1–11½  Nov. 22.  37–17–33
 
true observed Alt. 32–38–18½ 32–29–18½ 32–14–33 30–34– 3½ 12.  37–17–38
refraction + parallax   1–21½   1–22¼   1–22¼   1–28 9.  37–18–31
true alt. of ’s center 32–36–57 32–27–56¼ 32–13–11 30–32–35 8.  37–18–40
’s declinn Greenwich7  19–58–48   20–11–50   20–24–29   22– 9–15  13.  37–19–23
+8 at Poplar Forest 2–46  20– 1–34 2–41  20–14–31 2–36  20–27– 5 1–44  22–10–59 23.  37–19–44
true height of Æq. at P.F. 52–38–31 52–42–27 52–40–16 52–43–34 21.  37–21–29
90 90 90 90 298–29–24
Zen. dist. of Æq. = Lat. P.F. 37–21–29 37–17–33 37–19–44 37–16–26  37–18–40

MS (MHi); filed with TJ’s Weather Memorandum Book, 1802–16; written entirely in TJ’s hand on one side of a sheet, with his Calculations of Latitude of Willis’s Mountain, 8–9 Dec. 1816, on verso; partially dated.

Æq.: “equator.”

1Entry for this date canceled by TJ with a diagonal line.

2Number inserted by TJ in place of “69–15–30.”

3Manuscript: “1–11–11½.”

4Number inserted by TJ in place of “20?”

5Number inserted by TJ in place of “61–10–30.”

6At head of this column TJ canceled “Dec. 4” and readings of 30°–51′–45″ for half the observed altitude and 1′–11½″ for half the instrument error. In addition, TJ entered another reading for half of the observed altitude along the verso’s lower lefthand margin: “Dec. 5. 30°–15′–45″.”

7Manuscript: “Greewich.”

8Editorially corrected from minus sign in manuscript.

Index Entries

  • astronomy; and calculations of Poplar Forest’s latitude search
  • geography; and TJ’s calculations of latitude search
  • Greenwich Observatory, England; and prime meridian 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