232 MACHINERY IX CONNECTION WITH WATER. 



WAVES. 

 NATURE OF WAVES. 



An inverted syphon, or bent tube, like that shown in 

 fig. 259, may be used to exhibit the ^''^'- ''^^ 



principle on which depends the motion 

 of the waves of the sea. The action of 

 the waves on shores and banks, and the 

 inroads which they make upon farms 

 situated on the borders of lakes and 

 large rivers, present an interesting sub- 

 ject of inquiry. 



If the bent tube (fig. 259) be nearly filled with water, 

 and the surface be driven down in one arm by blowing 

 suddenly into it, the liquid will rise in the other arm. 

 The increased weight or head of this raised column will 

 cause it to fall again, its momentum carrying it down belo^v 

 a level, and driving the water up the other arm. The 

 surfaces will, therefore, continue to vibrate until the force 

 is spent. The rising and falling of waves depe'tid on a 

 ^similar action. The wind, by blowing strongly on a por- 

 tion of the water 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 add- 

 ed force of the wind upon it, until the vibrations increase 

 into large waves. 



THE WATER NOT TROGRESSIVE. 



The waves thus produced have a progressive motion 

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

 served. A curious optical deception attending this ad- 

 vancing 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 for- 

 ward with them j they pass underneath, now lifting it on 



