By introducing a time of relaxation in a wave equation for second sound (1) relations between the dispersion of second sound and ordinary sound are derived; (2) the high heat conductivity of He II is related to second sound in the same way as the normal heat conductivity is related to ordinary sound on Debye's theory; (3) values for the time of relaxation and the velocity of of the heat flow are computed which are practically the same as for the flow of liquid He II through narrow slits above the critical velocity, indicating that in both cases the restriction of the flow is due to the same mechanism.

• Received 15 October 1947

DOI:https://doi.org/10.1103/PhysRev.73.226