Columbia subject headings:
Harvard subject headings:
Astronomers--Germany--Correspondence.
Encke, Johann Franz, 1791-1865--Correspondence.
Humboldt, Alexander von, 1769-1859--Correspondence.
Scientists--Germany--Correspondence.
Princeton subject headings:
Astronomers--Germany--Correspondence.
Encke, Johann Franz, 1791-1865--Correspondence.
Humboldt, Alexander von, 1769-1859--Correspondence.
Scientists--Germany--Correspondence.