The important part of the present paper deals with the deriva tion of,besides Reynolds' equation of mean motion,a set of equations of tarbclent fluetuation and its solution. The latter set follows necessarily,if we subtract the former from the original Navier-Stokes differential equations.To solve these equations of turbulence we build velocity and velocity, velocity and pressure correlations of the second and third orders and the differential equations satisfied by themIt is shown that these equations containing correlations have no defite solution unless two new hypotheses are introduced:one of them is merely a mathematical approximation in nature and the aacond can be interpretel physically that turbulence is the sum of two parta:one depends upon the mean pressure gradient in the moving fluid while the other does not. The general theory is then applied to explain the pressure flow between two paralel planes. The restlt is in good agreement with observation.