On the attenuation and dispersion of first sound near the superfluid transition in He4

In this paper available measurements of the attenuation and dispersion of first sound near the superfluid transition in He⁴ are re-examined. Particular attention is given to the effect of the gravitational inhomogeneity upon the measurements, and the thermodynamic velocity is used to obtain the dispersion contribution from measured velocities at nonzero frequencies. The re-interpreted results are discussed in terms of current theories. Although there is partial agreement between experiment and theory, a number of aspects of the problem requires further theoretical and experimental investigation.