April 10, 1793 | Letter David Rittenhouse to Thomas Jefferson, April 10, 1793 David Rittenhouse asks Thomas Jefferson for direction in the planning of the Andrew Michaux expedition.
April 11, 1793 | Letter Thomas Jefferson to David Rittenhouse, April 11, 1793 Thomas Jefferson responds to David Rittenhouse's April 10 inquiry about planning Michaux's expedition and desires that the Philosophical Society meet.
July 3, 1796 | Letter Thomas Jefferson to Jonathan Williams, July 3, 1796 Thomas Jefferson discusses "barometrical measurements" of the Virginia mountains. Jefferson also notes his ongoing interest in agricultural researches.