em is more or less pervious to water,
and thus the water of the sea and of the rivers would slowly press its
way through the lower strata, and oozing up into the land beyond, would
soon make it all a swamp.

Then, besides the interpercolation from the soil, there is the rain. In
upland countries, the surplus water that falls in rain flows off in
brooks and rivers to the sea; but in land that is below the level of
the sea, there can be no natural flow of either brooks or rivers. The
rain water, therefore, that falls on this low land would remain there
stagnant, except the comparatively small portion of it that would be
evaporated by the sun and wind.

Thus you see, that if the people of Holland were to rely on the dikes
alone to keep the land dry, the country would become in a very short
time one immense morass.

To prevent this result it is necessary to adopt some plan to raise the
water, as fast as it accumulates in the low grounds, and convey it away.
This is done by pumps and other such hydraulic engines, and these are
worked in general by wind mills.

They might be worked by steam engines; but steam engines are much more
expensive than wind mills. It not only costs much more to make them, but
the expense of working them from day to day is very great, on account of
the fuel which they require. The necessary attendance on a steam engine,
too, is very expensive. There must be engineers, with high pay, to watch
the engine and to keep it always in order, and firemen to feed the
fires, and ashmen to carry away the ashes and cinders. Whereas a wind
mill takes care of itself.

The wind makes the wind mills go, and the wind costs nothing. It is
true, that the head of the mill must be changed from time to time, so as
to present the sails always in proper direction to the wind. But even
this is done by the wind itself. There is a contrivance by which the
mill is made to turn itself so as to face always in the right direction
towards the wind; and not only so, but the mill is sometimes so
constructed that if the wind blows too hard, it takes in a part of the
sails by its own spontaneous action, and thus diminishes the strain
which might otherwise be injurious to the machinery.

Now, since the advantages of wind mills are so great over steam engines,
in respect especially to cheapness, perhaps you will ask why steam is
employed at all to turn machinery, instead of always using the wind. The
reason is, because the wind is