The method founded by Einstein for the description of the acoustical behavior of a dissociating gas has been extended to cover a nondissociating gas in which five groups of internal energy states have different relaxation times. Since the resulting expressions are unwieldly, approximations based on them, which permit the rough description of experiment, have been given. The study of the variation of the velocity of sound with frequency demonstrates differences in the relaxation times of the various states. The variation of the velocity of sound with pressure shows in addition effects due to threehyphen;body collisions or to radiation from optically active states. It has been suggested to treat the temperature coefficient of the kinetic relaxation time by the introduction of an expirical quantity which may be called ``the activation energy of collision.'' By this means a rough kinetic analysis of the transition probability is possible. In gaseous mixtures, the relative spatial and energetic effectiveness of various types of collisions in exciting internal energy may be compared.
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