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 ${T}_{\ensuremath{\lambda}}\ensuremath{-}T$ from 1.3 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}2}$ to 5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}6}$ K. Using previously determined relationships for the specific heat, superfluid density, and thermal conductivity near the $\ensuremath{\lambda}$ point, consistency has been demonstrated between the measurements, velocities predicted by superfluid hydrodynamics, and certain scaling law predictions.