Second Sound in Liquid Helium II

A pulse technique for the propagation of second sound is described and the expected shape of the received pulse is discussed. In this connection, experimental evidence has been obtained for a temperature discontinuity at the interface between liquid helium II and a solid medium at second sound frequencies. The pulse method has been used to study the attenuation of second sound with distance and the formation of shock waves. The observations on the latter are shown to be in agreement with the predictions of the equations of motion of liquid helium II if second order terms are not neglected.