68 Flow to obtain tt. 
any account have it too small. It will do no harm by being 
made too big, and will give less trouble. Where the size can be 
given in width and depth the matter is simple, but sometimes this 
is not convenient. There may be an opening through which the 
water passes that cannot be easily altered, and which at the same 
time is too narrow for a screen to work. In such a case the 
screen must project into the pond, and may be on the rectangular 
system—that is, consisting of two sides and a front—or it may be 
made semi-circular, and in this case may be much wider than the 
outlet. In cases where there is much floating matter and heavy 
flooding, it may be commenced several yards from the outlet, 
beginning on the pond bank, and running out in semi-circular 
form until it reaches the bank again, a few yards on the other side 
of the outlet. It will be apparent, that the greater the dimensions 
of the screen the less will be the liability to become choked, and, 
consequently, the more easily will it be kept in working order. 
It is very desirable that a screen should be well fixed, that 
is, that it should be so let into the banks of the pond that there 
is no chance of the water flowing round it, or under it, instead of 
through it. This end can be attained by means of masonry or 
concrete, in which the screen may work, and which must be well 
puddled behind. A very simple and effective way of fixing a 
screen, when made of wood and perforated or woven metal, and 
one which I have frequently followed, is explained by the 
annexed diagram :— 
c 
Fig. z. 
