N. N. ANDREEV and I. G. RUSAKOV, Acoustics of a Moving Medium, GTTI, 1934, 40 pp., price 1 rub.

The work of N. N. Andreev and I. G. Rusakov is an original theoretical study of great importance for a number of applied questions of acoustics.

In essence, acoustic processes take place in a medium at rest. Often, it is true, the velocity of the medium is small and may be neglected, but in a number of important cases, such as: in the occurrence of noise from internal-combustion engines, the sound of a propeller and of artillery shells, in the propagation of sound in the atmosphere, etc., we are dealing with sound processes in a medium moving at high velocities. In wind musical instruments we likewise have to do with sound processes in a moving medium, although the velocities here are considerably smaller. Despite the great interest and importance of these questions, in contemporary textbooks and treatises on acoustics they are not given proper attention. More accurately, it should be said that this question has to date not been sufficiently developed, either from the theoretical or from the experimental side.

In their work the authors establish the fundamental equations of acoustics in moving media, considering acoustic oscillations as small disturbances superposed on a certain motion possessing a velocity potential. Under these conditions the solution of an acoustic problem reduces likewise to finding a certain velocity potential. By this method the authors solve the problem of the motion of sound in a medium moving with constant velocity, of the reflection and refraction of sound at the boundary of wind, and consider the question of the influence of a constant flow on the radiation of sound in tubes with a moving medium.

Although all these questions are considered only approximately and, as yet, in insufficient detail, it is quite clear that we have here the emergence of a new chapter of acoustics, exceptionally important for the theory of sound and for a number of applied disciplines.

Among the shortcomings of the work under review one should mention only the laconic character of the exposition, which makes it accessible only to a few specialists. It remains only to wish that the authors would analyze the various questions of the acoustics of moving media as comprehensively as possible and present them with greater completeness than has been done in the book that has appeared.

S. Rzhevkin