DISTINCTIVE FEATURES OF THE PROPAGATION OF SOUND WAVES IN A PERFECT GAS AT LOW PRESSUREA. N. Volobuev and A. P. Tolstonogov UDC 530 The minimum possible pressure at which a sound wave can propagate in a perfect gas has been found based on the dispersion relation. Using the molecular-kinetic theory it has been shown that this process can occur with such a minimum density when a quarter of a wavelength fits into the distance between molecules. A certain analogy between the propagation of a sound wave under these conditions and the propagation of an electromagnetic-energy quantum has been noted. Academician S. P. Korolev Samara State Aerospace University, Samara, Russia; email: firstname.lastname@example.org. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 76, No. 1, pp. 138-141, January-February, 2003. Original article submitted June 11, 2002.