IF g denote the intensity of surface gravity, the density of water, and h the elevation of the water surface above its mean position, the potential energy of the oceanic tide is ½g h2 per unit area. The kinetic energy must be comparable. If h has the equilibrium amplitude of 35 cm., the total energy of the ocean, the area of which is 3·7 × 1018 cm.2, must be about 2·2 × 1024 ergs.