THE FltEK ■WATJiU OK THE SOIL. 211 



actly tlemonstrated 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 

 exeicise of its adhesive attraction, the Liver of aqueous 

 particles which is in nearest contact is more strongly held 

 to it than the next outer layer, and the adhesion diminish- 

 es with the distance, itntil, 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, no\v, we bring in contact at a single point two 

 masses of the same kind of matter, one of Avhich is satu- 

 rated with hygroscopic water ;ind the other is perfectly dry. 

 It is plain tliat the outer layers of water-particles adhering 

 to the moist body come at once Avithin 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., is uni- 

 form o\'er the whole surface. 



If of two diff"erent 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 appiopriated 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 equWhv'ivm. Any cause which disturbs this 

 equilibrium at once sets up motion of the hygroscopic 

 water, which always j^roceeds from the more dry to thy 

 less dry body. 



