, pipes as in the one-inch pipe.

The ascertained instances of the obstruction of pipes, by excluding the
water from the joints, are very few. No doubt that clay, puddled in upon
the tiles when laid, might have this effect; but they who have
experience in tile-drainage, will bear witness that there is far more
difficulty in excluding sand and mud, than there is in admitting water.

It is thought, by some persons, that sufficient water to drain land may
be admitted through the pores of the tiles. We have no such faith. The
opinion of Mr. Parkes, that about 500 times as much water enters at the
crevices between each pair of tiles, as is absorbed through the tiles
themselves, we think to be far nearer the truth.

Collars have a great tendency to prevent the closing up of the crevices
between tiles; but injuries to drains laid at proper depths, with
two-inch pipes, even without collars, must be very rare. Indeed, no
single case of a drain obstructed in this way, when laid four feet deep,
has yet come within our reading or observation, and it is rather as a
possible, than even a probable, cause of failure, that it has been
mentioned.

HOW TO DETECT OBSTRUCTIONS IN DRAINS.

When a drain is entirely obstructed, if there is a considerable flow of
water, and the ground is much descending, the water will at once press
through the joints of the pipes, and show itself at the surface. By
thrusting down a bar along the course of the drain, the place of the
obstruction will be readily determined; for the water will, at the point
of greatest pressure, burst up in the hole made by the bar, like a
spring, while below the point of obstruction, there will be no upward
pressure of the water, and above it, the pressure will be less the
farther we go.

The point being determined, it is the work of but few minutes to dig
down upon the drain, remove carefully a few pipes, and take out the
frog, or mouse, or the broken tile, if such be the cause of the
difficulty. If silt or earth has caused the obstruction, it is probably
because of a depression in the line of the drain, or a defect in some
junction with other drains, and this may require the taking up of more
or less of the pipes.

If there be but little fall in the drains, the obstruction will not be
so readily found; but the effect of the water will soon be observed at
the surface, both in keeping the soil wet, and in chilling the
vegetation upon it. If proper peep-holes have been