February 12, 1799 | Letter Daniel Clark to Thomas Jefferson, February 12, 1799 Daniel Clark, of New Orleans, writes to Thomas Jefferson on behalf of Philip Nolan, promising a summary of Nolan's information and impressions about New Mexico and the Louisiana Territory. Clark also uses the letter to introduce Jefferson to the work of William Dunbar.
March 6, 1803 | Letter Andrew Ellicott to Thomas Jefferson, March 6, 1803 Andrew Ellicott writes of his willingness to train Meriwether Lewis in taking measurements on his trip westward.
March 14, 1803 | Letter Albert Gallatin to Thomas Jefferson, March 14, 1803 Albert Gallatin informs Thomas Jefferson of the preparations he has made for the Corps of Discovery expedition, including commissioning Nicholas King's blank projection of western North America. Gallatin demonstrates his familiarity with the work of cartographers including Arrowsmith, Delisle, and Mackenzie, assuming Jefferson has the same background knowledge.
April 3, 1803 | Letter Meriwether Lewis to Thomas Jefferson, April 3, 1803 Meriwether Lewis writes to Jefferson regarding his preparations, including his many communications with men of science. Lewis includes his plans for a collapsible boat.
April 30, 1803 | Letter Thomas Jefferson to Meriwether Lewis, April 30, 1803 Thomas Jefferson encourages Meriwether Lewis to follow Andrew Ellicott's advice on scientific matters involving astronomical measurements.