where C~ and C~ are the stationary aerodynamic lift and drag coefficients; the dash stands for the derivative with respect to the angle of attack a. The conclusions of [1] were verified on the experimental data published in [2]. Large vibrations (with amplitudes greater than a meter) of phase wires, mainly in the vertical direction along the O Y axis (Fig. 1), were observed repeatedly in high-voltage power lines. In the special literature such motions are called a dance or galloping of a single wire of a power line. Condition (1) was obtained by Den-Hartog [3] in studies of one-dimensional motion of a mechanical model of a wire as a necessary condition of self-excited vibrations in the vertical plane. Thus, the consideration of one-dimensional self-excited vibrations of an airfoil led to condition (1), which may rightfully be called the Glauert-Den-Hartog condition. It is interesting to note that , in our opinion, Russian researchers are not familiar with the paper of Glauert [1]. Thus, for example, there are no references to [1] in [4], although stability questions are considered, and other papers of Glauert are cited. Fedyaevskii and Blyumina [5] studied the conditions of loss of aerodynamic damping by an angle airfoil rotating about a fixed axis. They obtained a rather complex inequality containing moment aerodynamic coefficients and came to the conclusion (from experimental data) that condition (1), which they call DenHartog's condition, can also be used as a criterion. Therefore, in our opinion, it would be useful for researchers to know that the book-stacks of the Russian State Public Library of Scientific and Technical Literature contain rather complete sets of the Proceedings of the British Advisory Committee for Aeronautics for 1909-1980. Condition (1) was confirmed experimentally [5, 6] and has been applied in civil engineering. In designing skyscrapers, which are subjected to wind loads, the cross section of the building must be oriented so that the angles of attack with respect to the direction of prevailing winds are beyond the interval in which inequality (1) holds [71. In simulating the behavior of a power-line wire under the action of wind, Van'ko [8] considered motion of an airfoil with three degrees of freedom: motion along the O X and O Y axes and rotation about the center of mass (Fig. 1). The conditions of existence of static solutions of the system of equations of motion were established: if the airfoil is lifting and the lift Y ~ 0, equilibrium positions exist for any wind (air flow) velocity V > 0. In studies of the Lyapunov stability of possible equilibrium positions, the following results were obtained: