, in conformity with the rule we have stated; rapidly, if the
medium opposes little friction; slowly, if it opposes much. The
water so pushed in runs off by the drain, the column of pressure
being diminished in proportion to the water which runs off."

Mr. Thomas Arkell, in a paper read before the Society of Arts, in 1855,
says, on this point:

"The pressure due to a head of water of four or five feet, may be
imagined from the force with which water will come through the
crevices of a hatch, with that depth of water above it. Now, there
is the same pressure of water to enter the vacuum in the
pipe-drain, as there is against the hatches, supposing the land to
be full to the surface."

We do not find any intimation that there is any error in the view
advanced by the learned gentleman quoted; and if there is none, we have
an explanation of the faculty which water seems to have, of finding its
way into drainpipes. Yet, we feel bound to confess, that, aside from
authority, we should have supposed that the pressure due to a column of
pure water, would be essentially lessened, by the interposition of solid
matter between its particles.

CHAPTER XX.

EFFECT OF DRAINAGE ON STREAMS AND RIVERS.

Drainage Hastens the Supply to the Streams, and thus Creates
Freshets.--Effect of Drainage on Meadows below; on Water
Privileges.--Conflict of Manufacturing and Agricultural
Interests.--English Opinions and Facts.--Uses of Drainage
Water.--Irrigation.--Drainage Water for Stock.--How used by Mr.
Mechi.

The effect of drainage upon streams and rivers, has, perhaps, little to
interest merely practical men, in this country, at present; but the time
will soon arrive, when mill-owners and land-owners will be compelled to
investigate the subject. Men unaccustomed to minute investigation, are
slow to appreciate the great effects produced by apparently small
causes; and it may seem to many, that the operations of drainage for
agriculture, are too insignificant in their details, perceptibly to
affect the flow of mill-streams and rivers. A moment's thought will
convince the most skeptical, that the thorough-drainage of the wet
lands, even of a New England township, must produce sensible effects
upon the streams which convey its surplus water toward the sea.

In making investigations to ascertain what quantity of water may be
relied upon to supply a reservoir,