AND OTHER WATER WAVES 179 



steady current parallel to the shore is silent and 

 invisible. Yet all the water of the sea has this 

 lateral drift, including the wash-water of the 

 breaker. The motion of the stones which it then 

 carries is not simply up and down, but a zigzag, 

 the general direction of which is that of the 

 current's motion. 



Where small beaches are formed on the shores 

 of torrential rivers, small progressive waves charge 

 in upon them ; but here the current is more con- 

 spicuous than the wave, and I have then observed 

 ripples in coarse sand facing the shore and impelled 

 by the waves, whilst the coarse sand grains could 

 be seen to travel much faster' in the direction of the 

 current than in that of the wave. 



When, at sea, the wind is obliquely on-shore there 

 is not only a 'longshore current, producing the effect 

 explained above, but waves also break obliquely. 

 Their effect to drive shingle along the shore is then 

 obvious to the eye. On a gently sloping sandy 

 beach the waves running directly before the wind 

 cross the swell coming in from the offing. Just at 

 the breaker -line they combine with the swell and 

 cause it to break sooner than it otherwise would. 

 Thus a number of short, oblique breakers are pro- 

 duced where the crests coincide, and these drive 

 sand along the shore. 



