,
desert ground-waters are often exceedingly hard or alkaline, and,
therefore, are unfit for many uses.

In going to the high mountains for a supply, the author has struck a
principle of wide application. In many of the mountains of the Southwest
there are springs and small streams of excellent water. Often, as in the
case discussed, very little storage is required. These streams, however,
are absorbed or disappear before reaching even the mouths of the canons,
and the problem has been to convey the water to distant cities and
mining camps at reasonable cost. There are several cities in Arizona now
possessing pumped water supplies, which have possible gravity supplies
of superior quality. The writer believes that ultimately the gravity
supplies will replace the pumping plants.

In the Bonita pipe line, wood-stave pipe was used for the gravity
sections. In other localities, where the grade of the line is very
uniform, as would be the case down a typical clinoplain, cement pipe is
deserving of consideration. It would cost no more than wood stave, would
be more durable, and, furthermore, it need have no greater leakage. Its
cost, however, increases rapidly when built to withstand high pressures.

The use of bran for determining velocities is of interest. The results
are in close accord with those obtained from the weir measurements. In
the measurement of ground-water velocities by means of salts in
solution, it is found that the velocities of different filaments of
waters are extremely variable, and a quart of salt solution, after
moving forward a few feet, is widely dispersed. It would be of value to
know to what extent the bran was distributed during its 4-hour journey
through the pipe line, and during how many minutes it was being
discharged at the lower end of the line. Was the first appearance, or
the average time of appearance, accepted for computing the velocity of
flow?

KENNETH ALLEN, M. AM. SOC. C.E. (by letter).--From its lightness,
toughness, flexibility, and the facility with which it can be laid, wood
pipe has manifest advantages for use in inaccessible places and where
handling is difficult; loss in transportation is almost negligible, it
will stand much unequal settlement without cracking, and ordinary leaks
are easily repaired.

The coating of the bands is of such great importance that it should be
inspected very thoroughly, in order to remedy defects before the
back-filling is done. The writer has f