December 16, 1800 | Letter Thomas Jefferson to Caspar Wistar, December 16, 1800 Thomas Jefferson introduces Caspar Wistar to the work of William Dunbar, excited at the prospect of a scientific correspondent "on the very verge of the great terra incognita of our western continent."
December 16, 1800 | Letter Thomas Jefferson to Caspar Wistar, December 16, 1800 In a personal addition to his other letter of December 16, 1800, Thomas Jefferson assures Caspar Wistar of William Dunbar's fitness for membership in the American Philosophical Society.
February 28, 1803 | Letter Thomas Jefferson to Caspar Wistar, February 28, 1803 Jefferson informs Wistar of the upcoming expedition and of his faith in Meriwether Lewis.
April 27, 1803 | Letter Thomas Jefferson to Meriwether Lewis, April 27, 1803 Thomas Jefferson informs Meriwether Lewis he will be forwarding copies of his instructions for the journey into the Louisiana Territory. The instructions may be shown to members of the American Philosophical Society, in case they would make any modifications.
November 16, 1803 | Letter Thomas Jefferson to Meriwether Lewis, November 16, 1803 Thomas Jefferson updates Meriwether Lewis on political activity around the event of the Louisiana Purchase. Jefferson includes notes from the explorer Truteau that detail population and activities of some native groups living west of the Mississippi.