Precision sound-velocity measurements in He II

Acoustic resonators were used to measure simultaneously the velocities of first, second, and fourth sound in He II to a typical precision of 0.2%. Data were taken at temperatures from 1.2 K to the $\lambda$ line in 50-mK steps, and at pressures from the saturated vapor pressure to the melting curve in 1-bar steps. Temperature and pressure were determined to better than 0.1%. Fourth sound was measured in a coarse (∼ 1-μm) and fine (∼ 90-Å) packed powder. Smoothed and raw data values are tabulated for more than 1500 data points.