ABSTRACT
This chapter presents accounts of experimental work that has largely confirmed the validity of the two-fluid theory, dealing with channel flow, the properties of liquid helium films, thermal properties, and the various sound modes of Helium II (He II). The flow of He II at high velocities presents a complex experimental situation, in which it is difficult to distinguish between the many contributions to the dissipation of energy. D. Landau’s 1941 paper is undoubtedly the most influential single contribution to the development of the theory of He II. The basic two-fluid equations of motion were originally put forward by Landau; he treated superfluid flow by expressing the macroscopic hydrodynamical variables, density and velocity, as quantum mechanical operators, and showing that the equations of motion for these operators implied the continuity equation and Euler’s equation for an ideal fluid.
