ong
the whole length of five hundred feet, the stream will pass in a thin
sheet off on to the descending ground. The hill-side, immediately below
the gutter, is brought to a true grade and covered with grass. As its
inclination is much greater than would be admissible for sub-irrigation
drains, these are laid _obliquely_ in parallel lines at intervals of six
feet from one end to the other over the whole graded slope. These drains
are connected at their upper ends with the direct outlet-pipe leading
from the siphon chamber. They have an aggregate length of about ten
thousand feet. The method of operation is as follows:--

The capacity of the tank is supposed to equal about two days' discharge,
or about thirty-five hundred gallons; and the whole capacity of the
drains is about half that of the tank, so that the rapid emptying of the
whole volume into them will insure their being pretty thoroughly filled
from end to end. This arrangement will provide for the saturation of the
soil about once in two days, and will leave a sufficient interval
between the periods of saturation for the thorough dispersal and
aeration of the filth.

The extent to which this system will be interfered with by frost, it is
impossible to say. This will probably be less than would be supposed,
for the reason that the ground would often be covered with snow, and
that the sewage will have sufficient warmth to exert considerable
thawing influence. Whenever the discharge of the liquid through
irrigation pipes is shown to have become obstructed by freezing, it will
only be necessary to divert the flow, and turn it into the surface
gutter to be distributed over the ground.

It is possible that in this case, as in the one which has been under my
observation for six years past, there will be no interruption of the
working because of cold; but, should the interruption become serious, I
shall propose the planting of evergreen trees in parallel rows midway
between the drains. The protection that would thus be afforded, both by
the trees and by the drifting snow which they would gather, would
probably keep the ground free throughout the winter. Incidentally to the
chief advantage of this system, there will be, so long as the land is in
grass, quite an addition to its product.

* * * * *

There are hundreds of villages, with and without a water supply, where
the houses are too scattering and the street lengths too great to mak