> as lemmas

1944 F. Leib tr. E. Lifshitz in Jrnl. Physics (Moscow) 8 111/1 We look for the velocity v_s..in the ‘first’ and ‘second’ sound waves.

1944 J. Smorodinsky tr. V. Peshkov in Jrnl. Physics (Moscow) 8 381/1 There must be in this liquid [sc. helium] two kinds of periodic motions: the ordinary sound..and the so-called ‘second sound’.

1964 New Scientist 18 June 744/2 Second sound..is not really sound at all, but a heat wave that combines two potentially useful properties of sound and heat.

1975 Nature 2 Oct. 359/3 M. B. Robin..has..detected the heat pulse from a non-radiative transition by means of the ‘second sound’ pulse propagated in super-fluid helium and recorded by a superconducting lead bolometer.

1944 F. Leib tr. E. Lifshitz in Jrnl. Physics (Moscow) VIII. 111/1 We look for the velocity v_s..in the ‘first’ and ‘second’ sound waves.

1957 tr. L. D. Landau in Soviet Physics: JETP 5 102/1 It is shown..that in a Fermi liquid at absolute zero other waves can be propagated; these differ in nature from ordinary sound, and we shall call them waves of ‘zero sound’.

1959 K. R. Atkins in Physical Rev. 113 962 This article discusses the possible existence of two hitherto undetected types of wave propagation in liquid helium II. Third sound is a surface wave of long wavelength on a liquid helium film... Fourth sound may exist in narrow two-sided channels.

1959 K. R. Atkins in Physical Rev. 113 962 To discuss wave propagation in liquid helium II, it is necessary to write down two separate hydrodynamical equations, one for the superfluid component and the other for the normal component. In first sound the two components move in the same direction in phase, and there is a first-order oscillation of the density but only a second-order oscillation of the temperature. In second sound the two components move in opposite directions out of phase, and the temperature oscillation is then first-order while the density oscillation is only second-order.

1969 W. E. Keller Helium-3 & Helium-4 vi. 203 (caption) Attenuation and propagation velocity of sound in liquid He³ showing the characteristics associated with the transition from first sound to zero sound for two frequencies.

1974 D. J. Bergman in K. D. Timmerhaus et al. Low Temperature Physics—LT 13 I. 507 Following our experience with third sound, we may expect that in fourth sound, too, when the channels that hold the helium are sufficiently small so that the normal fluid motion is completely locked out, the only important source of attenuation will be conduction of heat into the walls of the helium channels.

1974 Nature 15 Mar. 194/3 The report..that they have observed the propagation of fourth sound in the two newly discovered phases of liquid ³He amounts to the first unequivocal evidence that both of these new phases are superfluids.

1976 Physics Bull. Aug. 351/2 ‘Zero sound’..corresponds to oscillations in shape of the Fermi surface.

1981 Nature 2 Apr. 359/2 Second sound is an unusual type of propagating wave mode, which can occur in superfluids, involving fluctuations in the local temperature and entropy of a medium rather than in the local density and pressure as found in a conventional sound wave.