Columbia subject headings:
Harvard subject headings:
Humboldt, Alexander von, 1769-1859--Correspondence.
Natural history--United States--History--18th century--Sources.
Natural history--United States--History--19th century--Sources.
Naturalists--Germany--Correspondence.
Scientists--Germany--Correspondence.
Princeton subject headings:
Humboldt, Alexander von, 1769-1859--Correspondence.
Intellectuals--United States--Correspondence.