Empirical and theoretical relations between wind, sea, and swell

Prior to the War there existed a wide gap between the theoretical knowledge of surface waves and the empirical knowledge of sea and swell, sea being defined as waves raised by the direct action of the wind, swell as waves that have emerged from a storm area and travel through regions of calm or weak winds. A few theoretical conclusions have been verified by experience. Thus, it had been established that the wind waves have, in general, the character of deep water waves for which speed, period, or length are interrelated.