CHAPTER XVII 



CAPILLARITY AND OSMOSIS 



98. Water Surfaces. A liquid is said to have its free surface 

 level, but this does not mean that it would conform to a 

 straight line. Since the earth is a sphere, the water level must 

 constantly curve. This curvature may easily be seen on a 

 long straight stretch of water such as a lake or canal. If a 

 telescope or field glass is fixed exactly horizontal at a certain 

 distance above the water and a target a mile or so away is 

 placed at the same height above 

 the water, it cannot be seen 

 through the glass, owing to the 

 curvature. A water surface is 

 considered level, however, when it 

 conforms to the curvature of the 

 earth. A well-known proverb 

 runs to the effect that "water 

 seeks its level." We find this _ _ 



true no matter what the shape of FIG. 37. Capillary attraction 



the vessel containing it happens fe -*?*** (Tower, Smith and 

 to be. If vessels of various shapes 



and sizes are connected at the bottom in such a way that 

 liquid is free to move from one to the other, pouring water 

 into any of the vessels will cause it to rise to the same height 

 in all of them. There are certain conditions, however, in 

 which water is not exactly level, even in ordinary vessels. If 

 we stand a sheet of glass on edge in a dish of water for instance, 

 and examine the point at which the surface of the water comes 

 into contact with it, we find that it curves upward here. The 



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