Superfluidity and Superconductivity

Abstract

I am sorry that Professor Landau was unable to come
\nfor two personal reasons. The first is that I have
\nworked on this problem of helium upon which he has
\nalso done so much, and I would have liked to have
\nspoken with him about it. The other reason is that I
\nwouldn't have had to give this lecture.