1Thomas Jefferson to Alexander von Humboldt, 6 March 1809 (Jefferson Papers)
Recueil d’observations astronomiques (Humboldt) [index entry]
2Alexander von Humboldt to Thomas Jefferson, 12 June 1809 (Jefferson Papers)
Recueil d’observations astronomiques (Humboldt) [index entry]
3John Vaughan to Thomas Jefferson, 20 August 1809 (Jefferson Papers)
Recueil d’observations astronomiques (Humboldt) [index entry]
4Alexander von Humboldt to Thomas Jefferson, 20 December 1811 (Jefferson Papers)
Recueil d’observations astronomiques (Humboldt) [index entry]
5Thomas Jefferson to Alexander von Humboldt, 6 December 1813 (Jefferson Papers)
Recueil d’observations astronomiques (Humboldt) [index entry]