396 NEWTON S PRINCIPIA. 



Professor Airy has also investigated the manner in 

 which the wind acts to raise the waves. His theoretical 

 conclusions are as follows : &quot; It is to be understood 

 that either from preceding disturbances, or from the trifling 

 inequalities of the wind while the water is smooth, there 

 are very shallow undulations upon the water. When the 

 wind begins to act, it will at first only increase the height 

 of the waves in every part, and during this time the heads 

 of the waves will be broken. But after a time the waves 

 beginning with the windward shore will be (for a short 

 distance at least) so much increased, that the power of the 

 wind will merely maintain them in that state without any 

 increase; but for all the sea in advance, the wind will 

 still be raising the waves. But as the waves successively 

 obtain that height which corresponding, according to our 

 result, with the height which the wind can just maintain, 

 these waves will no longer be increased, but the waves 

 in advance will still be increased. Thus a wind of given 

 intensity, however long it blows, can only raise the waves 

 at a given point to a certain height ; which height, how 

 ever, will depend upon the distance of that point from 

 the windward shore.&quot; 



