98 FOR BETTER CROPS IN THE SOUTH 



hub at Station 0: Station 1, three inches; Station 2, six inches; 

 Station 3, nine inches; Station 4, twelve inches. If it were 

 possible to sight over the top of these hubs, we would find that 

 they are in a straight line, and that this line has a uniform 

 slope of six inches to a hundred feet. 



All fields may not work out as simply as the above example, 

 so we will cite another case, which will show how to handle a 

 more complicated problem. Figure 6 shows that the elevation 

 of the different stations above Station is as follows: Station 

 1, one inch; Station 2, four inches; Station 3, six inches; Station 

 4, eighteen inches. Now, if we were to divide the eighteen inches 

 by four, giving a uniform fall of four and a half inches per fifty 



-** *— lUKL'QttT 3 " 



Fig. 6. 



feet, by the time we reached Station 3, we would be too close to 

 the surface of the ground with our tile line to obtain profitable 

 returns. In this case, we will consider only Stations 0, 1, 2, 

 and 3. w We will divide six, the elevation of Station 3, by three, 

 which will give a uniform fall of two inches per fifty feet. 

 Starting as before, we will drive the hub at Station 1 until it is 

 two inches higher than the one at Station 0, Station 2 will be 

 four inches higher, and Station 3, six inches higher. We will 

 now change the grade, and set the stake at Station 4, twelve inches 



The final hub showing change of grade 



(the difference between 18 and 6) above the stake at Station 3. 

 This will give the line a fall of twelve inches the last fifty feet. 



Grading — The three systems of grading that are generally 

 used are the target, the string, and the flow of water. Of these 

 the target system is the most accurate for all practical purposes 

 and the most generally used, and for this reason will be con- 

 sidered in this article. The string sometimes used is subject 

 to sag and is affected by the wind, thus making it unreliable 

 and not to be generally recommended. In some cases, where 

 the fall is unusually great, the flow of water might be used 

 satisfactorily. It is not to be recommended, however, because 

 of the impossibility of detecting small variations in the grade, 

 which will cause pockets in the tile line. These pockets soon 



