CAPILLARY ACTION 101 



finally obtained free from air and perfectly saturated 

 with water. The water level was then lowered till it 

 was i ft. below the surface, and was then maintained at 

 this point. The surface of the cylinder was then exposed 

 to a strong current of air (the velocity of which was 

 measured) for eight days, and the quantity of water evapo- 

 rated from the surface of the sand was ascertained. The 

 water-level was then successively reduced to 2, 3, and 4 ft. 

 below the surface, and at each stage the quantity of water 

 evaporated at the surface was ascertained ; each experiment 

 lasted from ten to twenty-four days. The trials were after- 

 wards repeated, using in place of sand a surface loam 

 (Wisconsin jth Rep.^ 151). The results were as follows : 



Water evaporated daily per Square Foot 



Fine Sand 

 Clay Loam 



The amount evaporated in each case . thus diminished as 

 the distance of the water-level from the surface increased. 

 Towards the close of the trials a slight white crust formed 

 on the surface of both sand and loam, this was removed 

 in the case of the loam, the rate of evaporation then rose to 

 1-27 Ib. per day. 



The quantity of water raised daily a distance of 4 ft. 

 by capillary action was thus at least J Ib. per square foot, 

 equal to a supply of about i inch of rain in five days, a 

 quantity quite sufficient for the most luxuriant growth *. 



- 1 The surface of a soil may be treated both so as to favour or retard 

 evaporation. When the surface of the wet sand was cut across with a knife 



