THE PROPERTIES OF SOIL 29 



with the water, will be found to become 

 entirely saturated. In respect of this property 

 soils vary greatly. Some can raise water 

 rapidly but not to a great height, others will 

 raise water slowly but, given time, the water 

 will reach a much higher level than in the 

 other case. It has been found that the 

 property largely depends upon the fineness 

 of the particles of soil, or, in other words, 

 on the size of the interstices between the 

 particles. Nowadays it is usual to speak of 

 the property, by the exercise of which water 

 rises in the soil, as " surface attraction," 

 each particle of soil covering itself with a 

 thin film of water, which diffuses from 

 particle to particle until the whole mass is 

 equally moist. Coarse sand, for instance, 

 does not raise water so effectively as sand with 

 finer grains ; clay, with its fine particles, 

 raises water rather slowly but to a com- 

 paratively great height. Humus facilitates 

 the rising of water and, therefore, improves 

 the conditions of sand. Of all the soils with 

 which a farmer has usually to do, fairly pure 

 sands are most likely to suffer from the effects 

 of drought in a season when rain is deficient. 

 Much, however, can be done to improve 

 matters by increasing the supply of humus, 

 so that a sand, comparatively barren in its 



