st iron, or of copper wire, to prevent the
intrusion of vermin. The screen should be movable, so that any
accumulation in the pipe may be removed. An arrangement of this kind is
shown in Fig. 40, as used in England. We know of nothing of the kind
used in this country. For ourself, we have made of coarse wire-netting,
a screen, which is attached to the pipe by hinges of wire. Holes may be
bored with a bit through even a hard tile, or a No. 9 wire may be
twisted firmly round the end of it, and the screen thus secured.

This has thus far, been our own poor and unsatisfactory mode of
protecting our drains. It is only better than none, but it is not
permanent, and we hope to see some successful invention that may supply
this want. So far as we have observed, no such precaution is used in
this country; and in England, farmers and others who take charge of
their own drainage works, often run their pipes into the mud in an open
ditch, and trust the water to force its own passage.

OF WELLS AND RELIEF PIPES.

In draining large tracts of land of uniform surface, it is often
convenient to have single mains, or even minors, of great length.
Obstructions are liable to occur from various causes: and, moreover,
there is great satisfaction in being certain that all is going right,
and in watching the operation of our subterranean works. It is a common
practice, and to be commended, to so construct our drains, that they may
be inspected at suspicious points, and that so we may know their real
condition.

For this purpose, wells, or traps, are introduced at suitable points,
into which the drains discharge, and from which the water proceeds again
along its course.

These are made of iron, or of stone or brick work, of any size that may
be thought convenient, secured by covers that may be removed at
pleasure.

Where there is danger of obstruction below the wells, relief pipes may
be introduced, or the wells may overflow, and so discharge temporarily,
the drainage water. These wells, sometimes called silt basins, or traps,
are frequently used in road drainage, or in sewers where large deposits
are made by the drainage water. The sediment is carried along and
deposited in the traps, while the water flows past.

These traps are large enough for a man to enter, and are occasionally
cleared of their contents.

When good stone, or common brick, are at hand, occasional wells may be
easily constructed. Plank or timber might be used; an