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 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 ( , 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; no. 4167; , 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