er, but the
gasoline engine has made it possible to propel aeroplanes through the
air.

CHAPTER XVIII

PUMPS AND THEIR VALUE TO MAN

181. "As difficult as for water to run up a hill!" Is there any one
who has not heard this saying? And yet most of us accept as a matter
of course the stream which gushes from our faucet, or give no thought
to the ingenuity which devised a means of forcing water upward through
pipes. Despite the fact that water flows naturally down hill, and not
up, we find it available in our homes and office buildings, in some of
which it ascends to the fiftieth floor; and we see great streams of it
directed upon the tops of burning buildings by firemen in the streets
below.

In the country, where there are no great central pumping stations,
water for the daily need must be raised from wells, and the supply of
each household is dependent upon the labor and foresight of its
members. The water may be brought to the surface either by laboriously
raising it, bucket by bucket, or by the less arduous method of
pumping. These are the only means possible; even the windmill does not
eliminate the necessity for the pump, but merely replaces the energy
used by man in working it.

In some parts of our country we have oil beds or wells. But if this
underground oil is to be of service to man, it must be brought to the
surface, and this is accomplished, as in the case of water, by the use
of pumps.

An old tin can or a sponge may serve to bale out water from a leaking
rowboat, but such a crude device would be absurd if employed on our
huge vessels of war and commerce. Here a rent in the ship's side would
mean inevitable loss were it not possible to rid the ship of the
inflowing water by the action of strong pumps.

Another and very different use to which pumps are put is seen in the
compression of gases. Air is forced into the tires of bicycles and
automobiles until they become sufficiently inflated to insure comfort
in riding. Some present-day systems of artificial refrigeration
(Section 93) could not exist without the aid of compressed gases.

Compressed air has played a very important role in mining, being sent
into poorly ventilated mines to improve the condition of the air, and
to supply to the miners the oxygen necessary for respiration. Divers
and men who work under water carry on their backs a tank of compressed
air, and take from it, at will, the amount required.

There are many forms of p