21Thomas Jefferson to John Vaughan, 28 June 1817 (Jefferson Papers)
American Philosophical Society; Transactions [index entry]
22Thomas Jefferson to Peter S. Du Ponceau, 7 November 1817 (Jefferson Papers)
American Philosophical Society; Transactions [index entry]
23Peter S. Du Ponceau to Thomas Jefferson, 5 January 1818 (Jefferson Papers)
American Philosophical Society; Transactions [index entry]
24Francis Adrian Van der Kemp to Thomas Jefferson, 7 January 1818 (Jefferson Papers)
American Philosophical Society; Transactions [index entry]
25Peter S. Du Ponceau to Thomas Jefferson, 22 January 1818 (Jefferson Papers)
American Philosophical Society; Transactions [index entry]
26Thomas Jefferson to Francis Adrian Van der Kemp, 9 February 1818 (Jefferson Papers)
American Philosophical Society; Transactions [index entry]
27Peter S. Du Ponceau to Thomas Jefferson, 14 February 1818 (Jefferson Papers)
American Philosophical Society; Transactions [index entry]
28Thomas Jefferson to David Hosack, [20 October 1819] (Jefferson Papers)
American Philosophical Society; Transactions [index entry]