THE FREE WATER OF THE SOIL. 211 
actly demonstrated in case of the force of gravity and 
electrical attraction, which act through great intervals of 
space. 
We must therefore suppose that when a mass of hygro- 
scopic matter is allowed to coat itself with water by the 
exercise of its adhesive attraction, the layer of aqueous 
particles which is in nearest contact 1s more strongly held 
to it than the next outer layer, and the adhesion diminish- 
es with the distance, until, at a certain point, still too 
small for us to perceive, the attraction is nothing, or is 
neutralized by other opposing forces, and further adhesion 
ceases. 
Suppose, now, we bring in contact at a single point two 
masses of the same kind of matter, one of which is satu- 
rated with hygroscopic water and the other is perfectly dry. 
It is plain that the outer layers of water-particles adhering 
to the moist body come at once within the range of a 
more powerful attraction exerted by the very surface of 
the dry body. The external particles of water attached 
to the first must then pass to the second, and they must 
also distribute themselves equally over the surface of the 
latter; and this motion must go on until the attraction 
of the two surfaces is equally satisfied, and the water is 
equally distributed according to the surface, i. e., 1s wni- 
form over the whole surface. 
If of two different bodies put in contact (one dry and 
one moist) the surfaces be equal, but the attractive force 
of one for water be twice that of the other, then motion 
must go on until the one has appropriated two-thirds, and 
the other is left with one-third the total amount of water. 
When bodies in contact have thus equalized the water 
§at their disposal, they may be said to be in a condition of 
hygroscopic equilibrium. Any cause which disturbs this 
equilibrium at once sets up motion of the hygroscopic 
water, which always proceeds from the more dry to the 
less dry body. 
