TILE DRAINAGE 



29 



surveyor to do the job. Where the fall is ample and less 

 accurate work is required, a home-made water level or 

 an ordinary carpenter's level, set on a straight-edge, may 

 be made to answer the purpose. These instruments are 

 illustrated in the cut following. When the total fall, 

 either of the main or laterals, is not quite as great as. 



Fig. 3. Different kinds of levels for determining grades. A, sur\-%yor's 

 level; B, carpenter's level; C, home-made water level. The water level is 

 made of half-inch gas pipe, with an upright five feet long and a cross piece 

 two feet long with elbows on the ends. Corks are put in the elbows and 

 pieces of glass tube inserted in the corks. The top of the upright is then 

 stopped and the cross piece filled with water so that it comes up in the glass 

 tubes. The instrument is used by standing it in the ground and sighting 

 along the water level in the two tubes to the rod. When being carried from 

 one place to another the ends of the tubes must be stopped to keep the 

 water in. 



is desired, it may be increased by making the drains a 

 little shallower at the upper ends. After the total avail- 

 able fall has been determined, divide it by the number of 

 fifty-foot spaces which the line contains; this, then, will 

 give the fall from one stake to the next. For example, 



