1Thomas Jefferson to William Clark, 8 September 1816 (Jefferson Papers)
astronomy; and observations of Lewis and Clark Expedition [index entry]
2William Clark to Thomas Jefferson, 10 October 1816 (Jefferson Papers)
astronomy; and observations of Lewis and Clark Expedition [index entry]
3Thomas Jefferson to Peter S. Du Ponceau, 7 November 1817 (Jefferson Papers)
astronomy; and observations of Lewis and Clark Expedition [index entry]
4Thomas Jefferson to Peter S. Du Ponceau, 30 December 1817 (Jefferson Papers)
astronomy; and observations of Lewis and Clark Expedition [index entry]
5Peter S. Du Ponceau to Thomas Jefferson, 6 January 1818 (Jefferson Papers)
astronomy; and observations of Lewis and Clark Expedition [index entry]
6Peter S. Du Ponceau to Thomas Jefferson, 14 February 1818 (Jefferson Papers)
astronomy; and observations of Lewis and Clark Expedition [index entry]
7Enclosure: Nicholas Biddle to William Tilghman, 6 April 1818 (Jefferson Papers)
astronomy; and observations of Lewis and Clark Expedition [index entry]
8Peter S. Du Ponceau to Thomas Jefferson, 14 April 1818 (Jefferson Papers)
astronomy; and observations of Lewis and Clark Expedition [index entry]