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We analyse the line-of-sight velocity field of ionized gas in the spiralgalaxy NGC 157 which has been obtained in the H\alpha emission at the 6mtelescope of SAO RAS. The existence of systematic deviations of the observedgas velocities from pure circular motion is shown. A detailed investigation ofthese deviations is undertaken by applying a Fourier analysis of the azimuthaldistributions of the line-of-sight velocities at different distances from thegalactic center. As a result of the analysis, all the main parameters of thewave spiral pattern are determined: the corotation radius, the amplitudes andphases of the gas velocity perturbations at different radii, and the velocityof circular rotation of the disk corrected for the velocity perturbations dueto spiral arms. At a high confidence level, the presence of the two giantanticyclones in the reference frame rotating with the spiral pattern is shown;their sizes and the localization of their centers are consistent with theresults of the analytic theory and of numerical simulations. Besides theanticyclones, the existence of cyclones in residual velocity fields of spiralgalaxies is predicted. In the reference frame rotating with the spiral patternthese cyclones have to reveal themselves in galaxies where a radial gradient ofazimuthal residual velocity is steeper than that of the rotation velocity(abridged).Comment: 23 pages including 25 eps-figures. Accepted for publication in A&

Restoring the full velocity field in the gaseous disk of the spiral galaxy NGC 157