1Thomas Jefferson to Alexander von Humboldt, 6 March 1809 (Jefferson Papers)
2Alexander von Humboldt to Thomas Jefferson, 12 June 1809 (Jefferson Papers)
3Alexander von Humboldt to Thomas Jefferson, 23 September 1810 (Jefferson Papers)
4William F. Gray to Thomas Jefferson, 18 May 1811 (Jefferson Papers)
5Enclosure: Thomas Jefferson’s Account with Joseph Milligan, [ca. 2 December 1811] (Jefferson Papers)
6Alexander von Humboldt to Thomas Jefferson, 20 December 1811 (Jefferson Papers)
7Henry M. Brackenridge to Thomas Jefferson, 25 July 1813 (Jefferson Papers)
8Thomas Jefferson to Alexander von Humboldt, 6 December 1813 (Jefferson Papers)
9Eusebio Valli to Thomas Jefferson, 5 June 1816 (Jefferson Papers)