Second-Sound Velocities, Superfluid Hydrodynamics, and Scaling Laws in Helium II

Direct measurements have been made of the velocity of second sound in liquid helium over the temperature range $T_{\lambda }-T$ from 1.3 × ${10}^{-2\mathrm{}}$ to 5 × ${10}^{-6\mathrm{}}$ K. Using previously determined relationships for the specific heat, superfluid density, and thermal conductivity near the $\lambda$ point, consistency has been demonstrated between the measurements, velocities predicted by superfluid hydrodynamics, and certain scaling law predictions.