Figure showing the direction of flow (relative to fixed axes) of particles in the neighbourhood
of a series of waves of constant form passing over the body of a model fish in the direction
of the large arrow. Leading surfaces are shown at fg, be, Ig, de. Trailing surfaces are shown at
nb, gh, cd, jk. The relative velocities of particles lying in the plane of a wave crest are shown
at the level hccx: the length and direction of the arrows at this level indicate the velocity and
direction of movement of the particles