162 Physics of the Soil. 



in height to which water may be raised in capillary tubes 

 by surface tension is found in the relation existing between 

 the volume of the tube and its internal circumference at 

 the level of the water surface. Quinke has shown that 

 the force of cohesion is exerted over a distance of suA 

 inch; so that when a glass tube is thrust into water the 

 molecules in the surface of the wall just above the water 

 draw upward upon the rows of molecules in the surface 

 lying nearest, raising them above the natural water level. 

 But as the edge of the surface film is raised the whole water 

 column is carried upward also until the weight lifted above 

 the hydrostatic level is equal to the cohesive attraction be- 

 tween the glass and the water. 



As each molecule of glass has a fixed power to pull, the 

 tube of large diameter will be able to lift as much more 

 water than the small one, as the number of molecules in 

 its circumference is greater. But the circumferences of 

 tubes increase in the same ratio as their diameters, and 

 hence a tube whose diameter is .1 inch will lift above the 

 water level 10 times as much water as the one .01 inch in 

 diameter. But, as the weight of water lifted increases as 

 the squares of the diameters of the tubes, the first tube 

 will only lift its column one-t^nth as high as the second 

 tube, for then its load becomes 10 times as great, and this 

 is the limit of its power, as expressed in the table below : 



The actual amount of water lifted by the surface film 

 stretched across the tube and carried upward by the 

 pull of the glass molecules just above its edge is as fol- 

 lows. 



