ORDER AMONG WAVES. 445 



track. It is even asserted, that such is the vio- 

 lence of this extraordinary phenomenon, which 

 is called by the Indians the Pororoca, that the 

 very islands tremble during its passage. 



The second order of waves are produced by 

 the action of the wind. Poets speak of the 

 " inconstant billow ;" and vainly, as might be 

 supposed, might we attempt to reduce to form 

 and law, the irregular and agitated movements 

 whiclx are now throwing the whole sea-surface 

 into tumult. Yet even here order reigns. 

 These waves, which give its restless aspect 

 to the sea, are of the class called oscillatory. 

 Mr. Russell's definition of them is that they 

 are gregarious, and of two species, progressive 

 and stationary. It appears that a certain de- 

 gree of adhesion takes place between a moving 

 mass of air and the water over which it sweeps. 

 The result is, that a certain portion of the 

 fluid is lifted above the general level of the 

 surface, and an oscillatory movement is thus 

 set up, which by the continued action of the 

 breeze is increased in magnitude, until waves 

 of considerable dimensions are formed. Waves 

 of this class exhibit a number of interesting 

 phenomena, into which it becomes not our 

 present inquiry to enter. In consequence of 

 perpetual changes in the direction of the over- 

 sweeping current of air, the direction and 



