Columbia subject headings:
Harvard subject headings:
Astronomers--Correspondence.
Humboldt, Alexander von, 1769-1859--Correspondence.
Schumacher, Heinrich Christian, 1780-1850--Correspondence.
Princeton subject headings:
Astronomers--Correspondence.
Humboldt, Alexander von, 1769-1859--Correspondence.
Schumacher, Heinrich Christian, 1780-1850--Correspondence.