172 FARMERS' INSTITUTES. 



d = diameter of pipe in feet, 

 h = rise of pipe. 

 1 = length of pipe. 

 Expressed as a rule it reads : 



To find discharge in cubic feet per second, multiply rise divided by letigthby 

 a f til power of diameter expressed in feet, extract square root of this product, 

 and tnultiply this result by 39^. 



Example. — Find discliarge in cubic feet per second, tile 1 foot diameter, 

 running full, fall divided by length equal ^i^. In this case Q = 39^>/7w 

 = 3.9. 



This formula may be reduced to a more useful form, in which we have 

 discharge in 24 hours instead of each second, in which case 



V = 6780\nj^j 



V = discliarge in cubic feet each 24 hours, 

 D == diameter of tile in inches. 



I" = rise divide 1 by length. 



If water one-half inch in depth were standing over one acre of land, it 

 would amount to 1815 cubic feet. 



By dividing above co-efficient by this amount we have 



A=3.8v/I> 



I 



In which A equals number of acres from which tile will remove water of 

 one-half inch in depth during 24 hours. 



The table following the article is computed from a formula somewhat 

 more accurate than the above, but the difference will in any case hardly be 

 sensible. 



WATER TO BE REMOVED. 



The capacity of the tile must be made dependent on this consideration, 

 and this varies in somewhat wide limits. If the rainfall is the only factor 

 involved, the difference in different localities is not as great as one would on 

 first consideration suspect ; the variation is probably in no case as great as 

 the variation in the annual rainfall. In case of water from other sources 

 just so much additional capacity must be given the drains. 



The annual rainfall is of very little imj^ortance in this consideration from 

 the fact that our drains to be of service must be able to remove the excess of 

 water much oftener than once per year. 



Suppose the annual rainfall to be about 36 inches or one-tenth of an inch 

 per day; if then the capacity of our drains were sufficient to remove thia 

 water, it might be thought that we should get good results. This would in- 

 crease the capacity given in the table five times. I have known systems of 

 drains to be put in on this plan, and although the investment was small for 

 tile, still so far as any returns were concerned, it was thrown away. Agri- 

 cultural crops do not flourish unless the water can be removed within a cer- 

 tain definite time after it falls. That period varies for different crops, and 

 under different systems of cultivation, but my observation leads me to 

 believe, it is not profitable to have this period longer than twenty-four hours. 



After long periods of drouth, the soil retains for a long time all the water 

 that falls upon it. Again during excessive wet weather, it gives off as much 

 as falls. Numerous experiments have been made to test the absorptive 

 powers of the soil; it varies very much with the soil and its condition, run- 

 ning from 10 to 90 pei cent, and over, of the weight of the soil. 



