28 ENGINEERING FOR LAND DRAINAGE. 



Capillary Motwment of Water. 



During the year 1 897 very satisfactory experiments 

 were conducted by the Division of Soils of the U. S. 

 Department of Agriculture for the purpose of determin- 

 ing the quantity of moisture present in soils at differ- 

 ent depths by means of the electrical method. This 

 method is based upon the changing electrical resistance 

 between two plates which are buried in the soil, and 

 consists in measuring the resistance by means of a 

 mechanism devised for the purpose. The study of the 

 results obtained by these experiments in connection 

 with the rainfall record and the drainage of the soil, 

 will well repay the agriculturist or engineer who is in- 

 terested in soil study. 



The table on p. 29, taken from Bulletin No. 12, 

 U. S. Department of Agriculture, Division of Soils, 

 is interesting and useful in showing the per cent of 

 w^ater carried by a soil at Washington, D. C, under 

 three different conditions: the first, growing wheat; 

 the second, cultivated bare, and the third, well 

 mulched. 



From other experiments noted in the same Bulletin 

 the following are selected for the purpose of showing 

 the per cent of clay and corresponding per cent of water 

 carried by the several soils noted, during the growing 

 season : 



At Newbern, N. C, on the best type of early truck 

 land the soil to a depth of three -or four feet has about 

 2.8 per cent of clay, and averages about 8,5 per cent 

 of water for the crop season. 



