, made in lengths of about 20 feet, and of the
following thicknesses:

1,349 linear feet, 0.083 inch thick.
220 " 0.095 "
240 " 0.109 "
250 " 0.120 "
320 " 0.134 "
610 " 0.148 "
1,450 " 0.165 "

Some of the iron was of the very poorest quality; the pipe was made by
contract in San Francisco, without the supervision of an inspector, as the
contractors were a firm of good reputation; the bad quality of the iron
was not detected until too late to have it corrected. Since then, the
writer has always had such pipes--the mines of which he has been the
manager using large quantities--made directly on the ground where they are
to be used; the pipe makers, in the latter case, always reject such sheets
as are too much below in thickness the standard gauge, and those which
show in passing through the rolls the bad quality of iron; tests of each
joint by hydrostatic pressure would add too much to the cost.

[Illustration: FIG. 16.]

The maximum tensile strain upon each of the seven thicknesses of iron used
was intended to be 16,500 pounds per square inch. Some of the sheets were
below the standard gauge, so that, in reality, the tensile strain is
sometimes as high as 18,000 pounds. The mean diameter of the pipe was
1.416 feet. The entrance into the pen-stock was tapered, so that the
coefficient of contraction was about 0.92. For pressures not exceeding say
380 feet, the joints were put together stove-pipe fashion. For greater
pressures, the joints were made by an inner sleeve riveted on one end of
the joint, with an outer lap-welded band, as shown by Fig. 15; lead was
run into the space between the outer band and the pipe, and then tightly
driven up by calking-irons. The pipe was laid under the bed of the Big
Canon Creek, a large stream when in freshet, where the head below the
hydraulic grade line was 760 feet. Some of the lead joints leaked slightly
at first, but this was soon remedied by more careful calking. No man-holes
or escape-gates were used. The pipe for the larger part of the year is not
filled at its upper end; when such is the case, the water at the inlet
carries down the pipe a great quantity of air, for which escapes must be
provided to prevent a jarring or throbbing, which would soon destroy the
pipe. The escape air-valves used are shown by Fig. 16. They consist simply
of a hea