which
forms a groove into which the pipes fall readily into line, and very
little seems to be said of collars in the published estimates of the
cost of drainage.

On this subject, we have the opinion of Mr. Denton, thus expressed:

"The use of collars is by no means general, although those who have
used them speak highly of their advantages. Except in sandy soils,
and in those that are subject to sudden alteration of character, in
some of the deposits of red sand-stones, and in the clayey subsoils
of the Bagshot sand district, for instance, collars are not found
to be essential to good drainage. In the north of England they are
used but seldom, and, in my opinion, much less than they ought to
be; but this opinion, it is right to state, is opposed, in numerous
instances of successful drainage, by men of extensive practice; and
as every cause of increased outlay is to be avoided, the value of
collars, as general appliances, remains an open question. In all
the more porous subsoils in which collars have not been used, the
more successful drainers increase the size of the pipes in the
minor drains to a minimum size of two inches bore."

_The form of the bore, or water passage_, in tiles, is a point of more
importance than at first appears. At one of our colleges, certain plank
sewers, in the ordinary square form, were often obstructed by the
sediment from the dirty water. "Turn them cornerwise," suggested the
professor of Natural Philosophy. It was done, and ever after they kept
in order. The pressure of water depends on its height, or head.
Everybody knows that six feet of water carries a mill-wheel better than
one foot. The same principle operates on a small scale. An inch head of
water presses harder than a half inch. The _velocity_ of water, again,
depends much on its height. Whether there be much or little water
passing through a drain, it has manifestly a greater power to make its
way, to drive before it sand or other obstructions, when it is heaped up
in a round passage, than when wandering over the flat surface of a tile
sole. Any one who has observed the discharge of water from flat-bottomed
and round tiles, will be satisfied that the quantity of water which is
sufficient to run in a rapid stream of a half or quarter inch diameter
from a round tile, will lazily creep along the flat bottom of a sole
tile, with hardly force sufficient to turn asi