1Thomas Jefferson to Alexander von Humboldt, 6 March 1809 (Jefferson Papers)
2Thomas Jefferson’s Account with Joseph Milligan, [8–10 March 1809] (Jefferson Papers)
3Alexander von Humboldt to Thomas Jefferson, 12 June 1809 (Jefferson Papers)
4Thomas Jefferson to John Vaughan, 31 August 1809 (Jefferson Papers)
5Lafayette to Thomas Jefferson, 12 March 1811 (Jefferson Papers)
6Thomas Jefferson to Alexander von Humboldt, 14 April 1811 (Jefferson Papers)