Velocity of Sound at 1 MHz Near theHe4Critical Point

Abstract

The velocity of 1-MHz sound waves has been measured in He 4 along several isotherms just above the critical temperature. The results indicate that along the critical isotherm, the quantity p/u 2 diverges approximately logarithmically as a function of J P-P c \ . Such a singularity at the critical point is to be expected in view of the corresponding singularity in C v . Additional velocity measurements were made in the saturated liquid, along isotherms several tenths of a degree above T c , and along the 4.5 and 5.0°K isotherms in the liquid. The specific-heat ratio has been calculated along the latter two isotherms and along the critical isotherm.