Flow to obtain it. 53 
is drawn by means of a sluice from the main stream. They are 
on the side of a hill, and the fall from one to the other is thus 
excellent. The aqueduct passes through cuttings and along em- 
bankments, and where watercourses of a dangerous nature cross 
its track they are carried over it by means of wooden shoots. The 
sluice box in this particular instance is two feet by one foot, and 
under no circumstances can more water be drawn from the stream 
than can pass through this box. A much smaller one than this, 
however, or a pipe, may often be used with great success. I have 
seen a series of ponds working very well that were supplied through 
a three-inch pipe. 
At the lower end of a long open aqueduct it is sometimes 
desirable to have-.another sluice and an overflow for waste water, 
as during heavy rains a good deal of surface water necessarily 
comes down. And here allow me to give a word of caution. 
Avoid lessening the regular supply from the stream at a time like 
this, or the water passing into the pond will contain too much of 
this surface water. Ponds supplied in such a manner, if properly 
made, are entirely under control and thoroughly workable. Too 
much water cannot get into them. On the contrary, during flood- 
time the quantity is found to lessen, as it is desirable to have a 
leaf screen in front of the sluice, and the flow of water is reduced 
by the mass of leaves or other floating matter brought down at such 
atime. I have found this arrangement work most satisfactorily— 
it is in fact the safety valve, and without such an arrangement in 
some form or other a pond or series of ponds is seldom safe. 
There are several ways of constructing a leaf screen. The 
simplest of all for the present purpose is to drive suitable wooden 
stakes into the bottom of the aqueduct, where the soil will allow 
of it. I make them of larch, and cut them three-sided rather than 
square, and about one to one and a half inches in diameter. 
Drive them all carefully so that the apex of the triangle formed by 
the three sides of each stake is up-stream, and then place a rail 
across their upper ends behind them, and nail each one to it. 
Should any of the ends stand higher than the rail, owing to not 
having been all driven the same distance into the ground, take a saw 
and cut them off. The rail may be nailed to posts driven into 
the bank at either end, or otherwise made secure according to 
