THE FLOW OF WATEK IN DKAIN TILE. 7 



To decrease the amount of work necessary to adjust the grade of 

 this continuous channel, the flume was rotated about its longitudinal 

 center. Thus, when changing grade, one half of the flume would be 

 lowered while the other half would be raised. The flume could be 

 set to any grade up to 1.50 feet in 100 feet. 



To enable the workmen to determine whether the flume was at the 

 proper grade, graduated wooden strips (A, PI. VI, fig. 1) 2 inches 

 wide, 0.5 inch thick, and several feet long were placed on each side 

 of the flume at each bent. The difference of elevation between 

 various grades at each bent had been previously computed, and these 

 differences were marked on the gage strips with the corresponding 

 grade number. Thus, when the proper mark appeared at the cross 

 board through which the gage strip ran, the workmen knew that part 

 of the flume to be at the desired grade. At points where the required 

 change of elevation was considerable, the flume was not raised or 

 lowered the entire amount at one time, but was changed by successive 

 increments of only a few inches. Thus the amount of stress on the 

 flume was lessened, and the liability of leakage through the possible 

 springing of the planks was eliminated. ' 



The grade of the flume was checked with an engineer's level im- 

 mediately before each experiment, to eliminate all possible errors 

 from inaccurate adjustment or from settlement of the vertical posts. 



LAYING THE TILE. 



The tile were laid on earth in the flume as in actual practice. 

 This earth in the bottom of the flume was about 7 inches deep. It 

 was placed in layers, 2 inches at a time, and each layer was thoroughly 

 tamped so that the bed on which the tile rested would not settle. 

 At first a line was stretched along the flume immediately over its 

 center and about 3 feet above the grade, and this line was used to 

 grade the bed for the tile. It was soon found, however, that the gage 

 line was in the way of the workmen, and another method for grading 

 the tile bed was adopted. The material for this method consisted of 

 a 30-inch strip, 2 inches wide and 0.75 inch thick, and a gage stick of 

 the same size but 17| inches long. The workman laid the strip 

 across the top of the flume and, holding the top of this gage stick 

 flush with the top of the cross arm, determined whether the invert of 

 each tile was at grade (P. VI, fig. 2) . 



COVERING THE THE. 



While blinding the tile, an engineer was constantly in the flume to 

 oversee the work and prevent any tile from being pushed out of line. 

 Fine earth, free from large clods, was used for blinding, the inspector 

 tamping the earth on each side of the tile with his feet. Thus any 

 appreciable movement or current of water through the earth on 



