In addition to the systems describing rotating liquid hydrodynamics traditionally applied to studying the motion of a top filled with a liquid, some recent papers treated systems with the Coriolis term as applied to various problems connected with the atmosphere and ocean dynamics [9, i0], to studying different wave motions in a liquid [ii] such as gravitational waves, inner waves resulting from the interaction of the Coriolis force with the pressure gradient, inertia waves (including the case of unbounded media), and acoustic waves in a compressible liquid. In all these problems the rotation of the Earth is taken into account; that is why the Coriolis term appears in the systems, which endows the solutions with specific features -there appears small waves changing in time in a sophisticated manner.