he dirt from the interior of the well instead
of a sand pump. As shown by Fig. 32 water under pressure is forced down
the small pipe _A_ which runs to the bottom of the well. The large pipe
_B_ can then, as the sand is loosened by the water, be driven down by
the one thousand-pound hammer _M_. The water and sand together flow up
in the space outside the small pipe and inside the large pipe,
overflowing through the waste pipe _W_. This type of well has been very
largely used throughout New York State; on Long Island, in connection
with the Brooklyn Water-supply; along the Erie Canal, in connection with
the Barge Canal Work, and in New York City, in connection with building
foundations.

[Illustration: FIG. 32.--Sinking a well by means of a water-jet.]

Sometimes, when a shallow dug well does not furnish the required
quantity of water, the amount of water can be increased by driving pipe
wells down into water strata below the one from which the dug well takes
its supply, so that water will rise to the strata penetrated by the dug
well. This has been done to increase the public supplies at Addison and
Homer in New York State. Unfortunately, much uncertainty exists in the
matter of the yield of driven wells, and an individual undertakes a deep
well usually with great reluctance on account of the expense involved
and the uncertainty of successful results. In level ground, conditions
are not likely to vary in the same valley, so that if one well is proved
successful, the probabilities are that wells in the vicinity will be
equally so, and yet, at some places, the contrary has proved to be true.

One may estimate the cost of putting down four-inch driven wells as
approximately one dollar per foot besides the cost of the pipe, which
will be about fifty cents per foot. The cost of one-and-one-half-inch
pipe would be considerably less than fifty cents, the cost of driving
varying not so much with the size of the pipe as with the soil
conditions. The writer recently paid ninety dollars for driving two
one-and-one-half-inch wells to a depth of about one hundred feet, the
above cost including that of the pipe; the soil conditions,
however, were very favorable. In Ithaca the cost of driving
one-and-one-quarter-inch pipe is fifteen cents per lineal foot up to
about fifty feet deep with the cost of the pipe fifteen cents per foot
additional. Below fifty feet deep the cost increases, since the labor
and time required for pulling up th