170 



Improved Agricultural Drainage Level. 



tion. In the example it is 40 inches. The numbers in column 

 fifth are added to, and those in column sixth subtracted from the 

 number at top of column seventh, as they succeed each other in the 

 two columns. 



Eighth — Contains the inches to be deducted from the inches 

 opposite in column seventh, that the drain may have an even and 

 uniform fall from its highest part to the outlet. These numbers 

 are obtained thus: — Add together the numbers in column second, 

 the sum is the whole length of the drain. Decide upon the fall 

 the drain should have for that length, or upon as much as 

 circumstances will allow. In this example it is made 36 inches, 

 which is put the bottom number in the column. For the num- 

 ber for each of the other stations multiply the distance of the 

 station from the first station or outlet by the inches of fall in the 

 whole length of the drain, and divide the product by the whole 

 length : the quotient will be the fall for that station. 



Thus for the fourth station. 



270 yards, distance from outlet. 

 36 inches, fall in the whole length. 



1620 

 810 



Length 455 yards )9720( 21^ inches fall from station fourth. 

 910 



620 

 455 



165 



Ninth— Contains the inches the depth for the drain from sur- 

 face of ground at each station, obtained by subtracting each of 

 the numbers in column eighth from that in the same line in 

 column seventh. 



Tenth. — The number of the stations. 



In the figure annexed, A is the bottom of drain at outlet. A B 

 the horizontal datum line. A 1, b2, d 3, f4, lib, B6, are the 

 depths given in inches in column seventh, a b, cd, ef, gh, CB, 

 are the depths given in inches in column eighth. A 1, a 2, c 3, 

 e 4, g 5, C 6, are the depths for the drain at the different stations 

 given in inches in column ninth. 



The line A C represents the bottom of the drain. 



As a check to the calculations, the difference of the sums of 

 columns third and fourth should be the same as that of columns 

 fifth and sixth, as should also the difference of top and bottom 

 number of column seventh. 



If the difference of level between two places is merely wanted 



