Columbia subject headings:
Harvard subject headings:
Germany--Relations--Russia--Congresses.
Russia--Relations--Germany--Congresses.
Science--Germany--History--19th century--Congresses.
Science--Russia--History--19th century--Congresses.
Princeton subject headings:
Germany--Relations--Russia.
Russia--Relations--Germany.
Science--Germany--History--19th century.
Science--Russia--History--19th century.