The constant-volume heat capacity of '*He has been measured at molar volumes from 20.45 to 29.71 cma/mole in the temperature range from 0.3 to 4 K. The entropy has been obtained as a function of volume and temperature by extrapolation of the data to 0 K. The P-T equilibrium curves below 2 K were obtained from the volume dependence of the entropy in the two-phase regions. The V-T curves were obtained above 1.25 K by observation of heat capacity discontinuities at the phase boundaries and below 1.25 K from the equilibrium pressure-temperature data and the properties of the pure phases. The minimum in the melting pressure occurs at 0.774 K and is 8.04 • 10-3 atm below the 0 K value. The corresponding maxima in the molar volumes of the solid and liquid were also determined. In the bcc phase (~S/t~V) x and (OCv/t~V) r are everywhere positive. Both the temperature and volume dependence of the heat capacity are similar to those of bcc 3He, in the very limited ranges of volume and temperature in which the phase could be studied. An unexpected rise in heat capacity in the 20 mK interval below the melting temperature was observed.

wen, Phys. Rev. Lett. 25, 1254 (this issue). jl R. Zwanzig and M. Bixon, Phys. Rev. A (to be published), give a hydrodynamical treatment of a related problem and obtain an expression for a D^^ which agrees with those obtained in Refs. 8 and 10 if the coefficient of self-diffusion is neglected. 12 Cf. L. Brillouin, J. Phys. (Paris) £, 153 (1936). 13 For similar reasons the existence of the transport coefficients in the Burnett hydrodynamical equations is not clear in three dimensions.The constant-volume heat capacity of liquid He 4 has been measured from 0.3 K to above the X point. Below 0.9 K the phonon heat capacity corresponds to a dispersion relation e=cp(l-~yp 2 ) withy varying from -4.1 xlO 37 g"" 2 cm"" 2 sec 2 at the saturated vapor pressure to 19.6xlO 37 g* 2 cm"' 2 sec 2 near the freezing pressure.

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