Abstract
The density of liquid $^{4}\mathrm{He}$ has been measured along the melting curve in the temperature range 0.1-0.82 K by observing the change with temperature of the resonant frequency of a superconducting microwave cavity immersed in the liquid. Relative changes in density as small as 4 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}9}$ could be resolved. From the results the entropy of solid $^{4}\mathrm{He}$ was obtained by using the Clausius-Clapeyron equation in conjunction with values for the isobaric-thermal-expansion coefficient and entropy of the liquid calculated from other data. No evidence for an anomalous linear temperature term in the entropy of the solid was found. The data are shown to be in good agreement with published measurements of the Debye temperature of the solid by Gardner, Hoffer, and Phillips.
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