Columbia subject headings:
Harvard subject headings:
Einstein, Albert, 1879-1955--Correspondence.
Foerster, Friedrich Wilhelm, 1869-1966--Correspondence.
Princeton subject headings:
Educators--Germany--Correspondence.
Einstein, Albert, 1879-1955--Correspondence.
Foerster, Friedrich Wilhelm, 1869-1966--Correspondence.
Physicists--Correspondence.