In 1909 Lord Raleigh established the general law of fluid flow: R = wV₂(f)(wVD/m), where R = resistance of flow, w = density of fluid, V = velocity of flow, D = diameter of pipe, m = viscosity of fluid, f = signifies function. For any particular value of (wVD)/m, using any combination of quantities, there will be a definite corresponding value of R/wV₂.