This paper treats of the fundamental problems in the theory of wings and airscrews, for the case in which we regard the disturbances due to the lifting system are small It' presents a critical view on Prandtl-Kussner's theory of acceleration potential. The funda- mental equations of the fluid motion may be reduced to the form of the classical wave equation and the velocity of propagation of the disturbances is equal to the velocity of sound. The object of the author is to show the aerodynamical interpretation of the characteristic properties of the classical wave equation. Especilly we translate into the language of aero- dynamics the well-known properties at Lorentz transformation in the theory of special relativity, and a number of interesting considerations are performed, for example, that Prandtl-Glauert's correction to lift is pointed out directly to be an example of Lorentz contraction, that there appears a sort of Doppler effect. The problem of time and causality has also an analogue there. We get different criterions according to the condition that the motion is subsonic or supersonic.
