Columbia subject headings:
Humboldt, Alexander von, 1769-1859.
Scientists--Correspondence.
Scientists--Germany--Biography.
Harvard subject headings:
Humboldt, Alexander von, 1769-1859.
Scientists--Correspondence
Scientists--Germany--Biography
Princeton subject headings:
Humboldt, Alexander von, 1769-1859--Biography.
Scientists--Correspondence.
Scientists--Germany--Biography.