This paper deals with the results of the investigation on the stability of the vertical salinity distribution effected with the wind velocity in Nakaumi Sea. In order to carry out this investigation, the author observed continually the vertical salinity distribution in Nakaumi Sea for a month running from Jan. 26, 1964 to Feb. 26 and analyzed the data obtained. To clarify the stability of the boundary or the diffusion from the lower salt water, the author applied the modified Richerdson's number R_<im> to this problem. And from this investigation, the following results were obtained.
( 1 ) The value of R_<im> calculated in each cases ranges from 0 to 23.7, i. e., the stability of the vertical salinity distribution in Nakaumi Sea is much more largely effected with the wind velocity than generally expected.
( 2 ) The value of C_f, coefficient of the friction resistance caused on the internal boundary plane is presumed to exist in order <10>^<-4>-<10>^<-6> (c. g. s.) and to have an inclination to proportinate inversely ⊿ρ, the difference of the density between the upper fresh water and the lower salt water.