1Thomas Jefferson to Alexander von Humboldt, 6 March 1809 (Jefferson Papers)
Mexico; A. von Humboldt’s work on [index entry]
2Alexander von Humboldt to Thomas Jefferson, 12 June 1809 (Jefferson Papers)
Mexico; A. von Humboldt’s work on [index entry]
3Thomas Jefferson to Alexander von Humboldt, 6 December 1813 (Jefferson Papers)
Mexico; A. von Humboldt’s work on [index entry]
4Eusebio Valli to Thomas Jefferson, 5 June 1816 (Jefferson Papers)
Mexico; A. von Humboldt’s work on [index entry]