Heckewelder, John / Du Ponceau, Peter Stephen (1819): A Correspondence Between the Reverend John Heckwelder, of Bethlehem, and Peter S. Duponceau Esq. […] Respecting the Languages of the American Indians. In: Transactions of the Historical and Literary Committee of the American Philosophical Society 1, S. 351–448
Erwähnt in:
- Wilhelm von Humboldt an Peter Stephen Duponceau, 00.05.1820
- Wilhelm von Humboldt an George Bancroft, 25.10.1820
- John Pickering an Wilhelm von Humboldt, 24.08.1821
- John Pickering an Wilhelm von Humboldt, 14.02.1823
- Wilhelm von Humboldt an Peter Stephen Duponceau, 09.04.1823
- Wilhelm von Humboldt an Peter Stephen Duponceau, 21.09.1827