THE WATER NOT PROGRESSIVE. 205 



and banks, and the inroads which they make upon 

 farms situated on the borders of lakes and large rivers, 

 present an interesting subject of inquiry. 



If the bent tube [Fig. 174) be nearly filled with wa- 

 ter, and the surface be driven down in one branch by 

 blowing suddenly into it, the liquid will rise in the 

 other branch. The increased weight or head of this 

 raised column will cause it to fall again, its moment- 

 um carrying it down below a level, and driving the 

 water up the other branch. The surfaces will, there- 

 fore, continue to vibrate until the force is spent. The 

 rising and falHng of waves depend on a similar action. 

 The wind, by blowing strongly on a portion of the wa- 

 ter of the lake or sea, causes a depression, and produces 

 a corresponding rise on the adjacent surface. The 

 raised portion then falls by its weight, with the added 

 force of the wind upon it, until the vibrations increase 

 into large waves. 



THE WATER NOT PROGRESSIVE. 



The waves thus produced have a progressive motion 

 (for reasons to be presently shown), as every one has 

 observed. A curious optical deception attending this 

 advancing motion has induced many to believe that 

 the water itself is rolling onward ; but this is not the 

 fact. The boat which floats upon the waves is not 

 carried forward with them ; they pass underneath, now 

 lifting it on their summits, and now letting it sink into 

 the hollows between. The same effect may be observ- 

 ed with the water-fowl, which sits upon the surface. 

 It often happens, indeed, that the waves on a river roU 

 in an opposite direction to the current itself 



