AGENTS AT WORK IN THE OCEAN 223 
(an elliptical rise and fall), and the other the wave 
passage itself, which is horizontal, and merely a 
transmission of motion, not a bodily transfer of the 
water. When the wind is blowing there is a third 
movement, a slow drift or current of the surface water 
carried in the direction of the wind. Therefore, a 
floating object will move forward a little, though never 
nearly so fast as the wave form. 
Reaching the shallower water of the coast, the wave 
begins to change its habit (Fig. 124). It is a disturb- 
ty ® 
S 
Fic. 124. 
Diagram to show approach of a wave upon a beach. 
ance of the water extending to a depth of several 
feet or yards, and in great waves several score of feet. 
In the open sea this can proceed with no other 
interference than that of the water itself, but on the 
shallowing coast the true wave movement is partly 
checked. The wave then travels faster at the top 
than at the bottom; it overtopples and rushes upon 
the coast as a breaker, hurling tons of water against 
the shore with terrific force (Fig. 125). Often- 
times the onset of the wave is vigorous enough to 
move bowlders several tons in weight. At the same 
