VISCOSITY RETARDS UNDERGROUND CIRCULATION. 153 



THE FACTOR OPPOSlMi 1VATKR t II!( TLATIOX. 



The factor opposing water circulation is internal friction of the water. 

 The internal friction is dependent upon the viscosity of the solutions. The 

 elements entering into viscosity are the concentration of the solutions and 

 the temperature. The more concentrated the solutions the greater the 

 viscosity ; but as the underground solutions of water are commonly not 

 strong, this is ordinarily not an important element. The viscosity of water 

 decreases very rapidly with increase of temperature. The relative viscosity 

 of pure water at 0° C, 45° C, and 90° C. is respectively 100.00, 33.89, and 

 18.16. (See p. 141.) From these ratios it is apparent that the viscosity of 

 water at 45° C. is about one-third of that at 0° C, and at 90° C. only about 

 one-fifth of that at 0° C. 



It is therefore clear that the higher the temperature the less the 

 viscosity and the less the internal friction. Internal friction due to viscosity 

 results from the variable speeds of different parts of moving water columns 

 and from the friction between the moving and fixed portions. The greater 

 the variations in speed of the moving parts the greater the internal friction 

 due to this cause. 



Water usually wets the surface of the rocks. In other words, there is 

 molecular attraction between the water solutions and the minerals com- 

 posing the rocks. This attraction is so strong that a thin film of water is 

 firmly held by the walls of the openings — so firmly that it may be consid- 

 ered as fixed; at least the only interchange which occurs between it and 

 the passing water "currents is that of diffusion, not that of flow. Daniell 

 says the friction between the layer of adherent water and the rock is 

 infinite as compared with the friction within the liquid.* 1 That the friction 

 is between the moving liquid and the fixed film of liquid is shown by the 

 fact that for any liquid the composition of the walls has no effect upon the 

 flowage. 6 This being the case, it is clear that in the flowage of water 

 through tubes there is no friction of the water against the rock walls. The 

 adherent films of water are the walls of the moving columns, and the internal 

 friction between the water and the walls is that between the fixed films and 

 moving water. 



« Daniell, Alfred, A text-book of the principles, of physics, 3d ed., Macmillan Co., New York, 

 1895, p. 306. 



a Daniell, cit., p. 316. 



