How to obtain tt. 69 
A B is a bar of wood, underneath which is the wire or perforated 
screen, as shewn. On the outer ends of this bar, where it 
extends to C and D, are nailed several boards. Another cross 
bar lies at the back of the boards just below the screen, e to f, 
and another at the bottom of all, g to 4. The whole of the wood- 
work below the dotted line 4, 4, m, 2, 0 is to be buried in the 
bottom and banks of the raceway, and, in constructing it, the 
screen should be made of a suitable size to fit the raceway, 
unless it be intended to use a projecting one. In such a case 
no screen is fitted into the opening below A B, but the projecting 
one may be fixed to the woodwork, and instead of working in the 
raceway it works in the pond. There is a great advantage in 
using wood, inasmuch as joints, alterations, and repairs are easily 
made. It is true that it is more liable to decay than stone, but it 
lasts a long time, and is not so often damaged by frost, and it has 
the advantage of being less expensive and more easily adapted 
than masonry. It should always be charred, both for the sake of 
preservation, and to prevent the growth of fungus (Saprolegnia. ) 
A screen constructed in this way will be found a very simple 
affair, and the filling of the trench which has been dug to receive 
it, if properly done, will render it perfectly tight and secure. If 
the work be done in concrete or masonry the principle is still the 
same, and will ensure safety unless it has been very clumsily 
managed indeed. The screen can be made to slide in a groove or 
be a fixture, as may be most desired. 
There is not much fear of the water getting round or under- 
neath such a screen, and it will be found to be worth the labour 
expended upon it. Fully three-fourths of those I have come 
across which have been made in some other way have been 
found to be useless. Once I was called to inspect a small lake 
that had been stocked by an enterprising hotel proprietor. The 
fishing had not improved as it should have done. We made a 
careful survey of the water and its surroundings, and on 
approaching the outlet one of the causes of failure was very 
apparent. The outlet screen consisted of a big wooden frame 
with perpendicular iron bars, but it was choked up so that no 
water could pass through it, and instead of doing so it was escaping 
through a hole which it had washed out round the end of the 
