DISCHARGING THE WATER. 109 



when the reservoir is full will discharge until the water is 

 exhausted, into the distributing furrow, #, fig. 44, and I, 

 b, fig. 45. The dotted line, in fig. 44, shows the level of 

 the water in the reservoir when it is full and overflowing 

 at the outlet, a. 



When the reservoir is filled, the surplus is discharged 

 on each or either side, by the channels made for that pur- 

 pose. This will obviate the difficulty previously pointed 

 out. The flow may then be turned upon the upper por- 

 tion of the meadow for twelve hours, in such a manner 

 that the whole of the water shall be absorbed by the soil, 

 and afterwards the contents of the reservoir may be flow- 

 ed on to the lower portion during the next twelve hours, 

 when the outlet will be closed. Many different arrange- 

 ments for the use of the water may be devised to meet 

 the necessities of any peculiar case, and as experience is 

 gained, any difficulty that may arise at the first will be 

 readily overcome. The reservoir may be discharged by 

 an intermittent self-acting arrangement which is either a 

 siphon, already described, or a more complicated but 

 equally effective method of a balanced trap, fig. 46. The 

 balanced trap consists of a board having a weight, H, at- 

 tached to one end, and a cup or basin at the other, and 

 being suspended upon pivots in a frame erected at the edge 

 of the main distributing ditch at the outlet in front of 

 the dam. The board is nicely balanced, so that when the 

 basin is empty the weighted end rests upon a prop, F, pur- 

 posely placed for it ; but when the basin is filled with 

 water it overbalances the weight and falls. As it falls it 

 releases a gate, /, upon which is fixed a leather cushion 

 which closes the outlet pipe of the reservoir, M. When 

 the reservoir is empty the gate is raised and the pipe is 

 closed. When the reservoir is filled the overflow enters a 

 pipe through the upper part of the dam, (7, and flows into 

 the basin. The basin descends and releases the gate ; the 

 force of the water flowing from the discharge pipe keeps 



