The interaction of a gravitational wave (G.W.) with substances causes periodical changes of their density. These changes may be fixed either by means of piezocrystals (just as in Weber's arrangement [1], for example) or by means of the light scattering on the sound aroused by G.W. It is of great interest the utilization of substances' critical states as a detector; the large compressibility of the former affords the maximum of possible changes of their density in a definite gravitational field. They have discussed one kind of experiment in [4] (denoted here as I) in which the presence of the gravitational flow caused periodical changes of the freguency of the light scattered on the fluctuations of one of the components of the two – component solution in its critical state of stratification.