ely used in
California than in any other part of the world, for conveying large
quantities of water which is required for hydraulic mining, for
irrigation, for the supply of towns and for transporting timber. The
flumes are frequently carried along precipitous mountain slopes, and
across valleys, supported on trestles. In Fresno county, California,
there is a flume 52 m. in length for transporting timber from the Sierra
Nevada Mountains to the plain below; it has a rectangular V-shaped
section, 3 ft. 7 in. wide at the top, and 21 in. deep vertically. The
boards which form the sides are 1-1/4 in. thick, and some of the
trestlework is 130 ft. high. The steepest grade occurs where there is a
fall of 730 ft. in a length of 3000 ft. About 9,000,000 ft. of timber
were used in the construction. At San Diego there is a flume 35 m. long
for irrigation and domestic supply, the capacity being 50 ft. per
second; it has 315 trestle bridges (the longest of which is that across
Los Coches Creek, 1794 ft. in length and 65 ft. in height) and 8
tunnels, and the cost was $900,000. The great bench flume of the
Highline canal, Colorado, is 2640 ft. in length, 28 ft. wide, and 7 ft.
deep; the gradient is 5.28 ft. per mile, and the discharge 1184 ft. per
second.

Aqueduct in iron piping.

As previously stated, the type of aqueduct built of concrete, &c., can
only be adopted where the ground is sufficiently elevated to carry it,
and where the quantity of water to be conveyed makes it more economical
than piping. Where the falling contour is interrupted by valleys too
wide for a masonry structure above the surface of the ground, the
detached portions of the built aqueduct must be connected by rows of
pipes laid beneath, and following the main undulations of, the surface.
In such cases the built aqueduct terminates in a chamber of sufficient
size to enclose the mouths of the several pipes, which, thus charged,
carry the water under the valley up to a corresponding chamber on the
farther hillside from which the built aqueduct again carries on the
supply. These connecting pipes are sometimes called siphons, although
they have nothing whatever to do with the principle of a siphon, the
water simply flowing into the pipe at one end and out at the other under
the influence of gravity, and the pressure of the atmosphere being no
element in the case. The pipes are almost always made of cast-iron,
except in such cases as the lower part of some siph