38 AGRICULTURE 



the supplies provided directly or indirectly 

 by rain or melted snow, it may be mentioned 

 that soil, in common with many other sub- 

 stances, has the power of condensing a 

 certain amount of water from the vapour 

 naturally present in the atmosphere, and 

 such water is not without influence in the 

 soil. This property of soil may be demon- 

 strated by thoroughly drying a small quantity 

 in an oven and then leaving it exposed in a 

 room. If the weight of the soil be accurately 

 determined immediately after drying, and 

 again after exposing to the air for two or 

 three hours, it will be found that the soil has 

 undergone considerable increase in weight, 

 and it is not difficult to prove that this 

 increase is due to the condensation of moisture 

 from the atmosphere. Certain of the con- 

 stituents of soil, notably humus, have this 

 power to a greater extent than others ; 

 while some artificial manures, e.g. kainit and 

 nitrate of lime, act in a similar manner, and 

 to an even greater extent ; but it is doubtful 

 whether artificial fertilizers are ever applied in 

 such quantity as to have any appreciable influ- 

 ence upon the total water contents of the soil. 

 The soil has not only interesting and use- 

 ful relationships with water, but certain of 

 its properties as regards heat are also of 



