THE TIDES. 145 



of the wind produces ripples and waves of every 

 size, it also produces a heaping-up of the water 

 as illustrated by this diagram (Fig. 19). Suppose 

 we have wind blowing across one side of a sheet 

 of water, the wind ruffles the surface, the waves 

 break if the wind is strong, and the result is a 

 strong tangential force exerted by the wind on 

 the surface water. If a ship is sailing over the 



FIG. 19. Showing the heaping-up of water produced by wind. 



water there is strong tangential force ; thus the 

 water is found going fast to leeward for a long 

 distance astern of a great ship sailing with a side 

 wind : and, just as the sails of a ship standing 

 high above the sea give a large area for the wind 

 to act upon, every wave standing up gives a 

 surface, and we have horizontal tangential force 

 over the whole surface of a troubled sea. The 

 VOL. ill. L 



