Columbia subject headings:
Humboldt, Alexander von, 1769-1859--Congresses.
Humboldt, Wilhelm von, 1767-1835--Congresses.
Harvard subject headings:
Humboldt, Alexander von, 1769-1859--Congresses.
Humboldt, Wilhelm von, 1767-1835--Congresses.
Princeton subject headings:
Humboldt, Alexander von, 1769-1859--Congresses.
Humboldt, Wilhelm von, 1767-1835--Congresses.