Columbia subject headings:
Humboldt, Alexander von, 1769-1859.
Lejeune Dirichlet, Peter Gustav, 1805-1859.
Scientists--Correspondence.
Harvard subject headings:
Humboldt, Alexander von, 1769-1859.
Lejeune Dirichlet, Peter Gustav, 1805-1859
Scientists--Correspondence
Princeton subject headings:
Mathematicians--Correspondence.
Scientists--Correspondence.