1Thomas Jefferson to Alexander von Humboldt, 6 March 1809 (Jefferson Papers)
Humboldt, Friedrich Wilhelm Heinrich Alexander, Baron von; Voyage de Humboldt et Bonpland [index...
2John Vaughan to Thomas Jefferson, 20 August 1809 (Jefferson Papers)
Humboldt, Friedrich Wilhelm Heinrich Alexander, Baron von; Voyage de Humboldt et Bonpland [index...