t of apparatus nor in
operation. The principle is shown by the diagram of Fig. 23, and
explains without words how air pressure may be carried down into the
well through one pipe and thereby force the water of the well up into
another pipe far above its natural level. The machinery needed involves
an engine or motor and an air compressor, the latter taking the place of
the ordinary pump. It has the single advantage that it avoids the
maintenance of valves and similar deep-well machinery at a great
distance below the ground, the air pump not requiring any mechanism in
the well.

In Fig. 50 is shown a plant installed by the Knowles Pump Co. for a
hotel where the air compressor furnished compressed air to raise the
water from the deep well into a tank, whence a steam pump lifts the
water to a reservoir, not shown.

[Illustration: FIG. 51.--Wooden tank.]

_Water tanks._

The standard form of wooden tank in which water may be stored and from
which it may be delivered to the house fixtures is pictured in Fig. 51.
Figure 52 shows a galvanized iron tank for the same purpose. The tables
appended, taken from catalogues of firms building such tanks, show the
dimensions, weights, and costs of the two kinds of tanks.

TABLE XV. DIMENSIONS AND LIST PRICES OF WATER TANKS.

WOODEN STAVE TANKS

======+=======+=========+=====+======+=============+=============+=============
| | | | | 1-1/2 In. | 2-In. | 2-In.
Length| | | |Price | Cypress | Cypress | Pine
Of | Dia. | | No.|Galv. +------+------+------+------+------+------
Stave,|Bottom,|Capacity,|of |Hoops,|Weight| |Weight| |Weight|
Feet| Feet | Gallons |Hoops|Extra | Lb. | Price| Lb. | Price| Lb. | Price
------+-------+---------+-----+------+------+------+------+------+------+------
2 | 3 | 66 | 2 |$ .30 | 105 |$ 9.30| 127 |$12.00| 110 |$10.50
3 | 3 | 108 | 3 | .40 | 146 | 12.00| 182 | 15.00| 157 | 13.20
2 | 4 | 125 | 2 | .35 | 150 | 14.30| 186 | 17.50| 160 | 15.50
4 | 4 | 283 | 4 | .65 | 260 | 21.00| 321 | 26.00| 277 | 23.00
2 | 5 | 207 | 2 | .45 | 190 | 19.80| 240 | 24.00| 207 | 21.00
2-1/2| 5 | 272 | 3 | .65 | 247 | 21.30| 305 | 26.00| 263 | 23.50
3 | 5 | 337 | 3 | .65 | 267 | 22.80| 332 | 28.00| 287 | 25.00
4 | 5 | 467 | 4 | .85 | 342 | 25.80|