The constant of proportionality in Jeffreys's expression for the work done by the wind on the sea surface. It was assumed by Jeffreys that this work is proportional to the product of the density of air, the slope of the water surface, and the square of the wind velocity relative to the wave. Although the value of the sheltering coefficient (0. 27) found by Jeffreys gives a satisfactory explanation of the initial formation of wind waves, observations of the increase of wind waves shows that this value is about ten times too high for the subsequent transfer of energy from wind to waves.