in dry weather, since it promotes capillary action by reducing the soil spaces.
Capillarity and Surface Tension.-Reference should be made to the article Capillary Action for the general discussion of this phenomenon of liquids.
Laplace was, moreover, the first to offer a complete analysis of capillary action based upon a definite hypothesis - that of forces "sensible only at insensible distances"; and he made strenuous but unsuccessful efforts to explain the phenomena of light on an identical principle.
By this capillary action water may be transferred to the upper layers of the soil from a depth of several feet below the surface.
If material systems are constituted of discrete atoms, separated from each other by many times the diameter of any of them, this simple plan of exhibiting their interactions in terms of direct forces between them would indeed be exact enough to apply to a wide range of questions, provided we could be certain that the laws of the forces depended only on the positions and not also on the motions of the atoms. The most important example of its successful application has been the theory of capillary action elaborated by P. S.