The construction of artesian wells depends upon the fact that water,
being at liberty to flow, will always sink to a level; by which it
is meant that the parts which are highest press upon those that are
lower, and tend to raise them, the higher parts sinking in the same
proportion that the lower parts are elevated; this continues until
both are upon a level. Suppose a bent glass tube of the form of fig.
1, be partly filled with water, the surfaces of the water in both
arms of the tube will each be upon a level with the other; suppose
now another such tube to have a small hole at A, the water sinking
in each arm will force out a jet of water, and if a tube be inserted
into this hole it will represent an artesian well, and the water will
rise in it till all three are on a level (fig. 2). Instead of these
tubes there is a layer of some porous material, as gravel, at some
distance beneath the surface of the earth, rising at each end and
forming a sort of basin (fig. 3), which is bounded above and below
by some impervious substance as clay or stone; the well being sunk
at any part (as at _a_, _b_, or _c_) below the level of the gravel,
where it forms the surface of the earth, must cut through the upper
stratum of clay or stone, and thus form a tube into the porous gravel
which holds the water; this water is obtained from the rain, which,
falling on the surface of the earth, drains through the gravel and
fills its lower part. The water will rise in the bore at a height
according to circumstances, if the gravel at each side of the bore
rises to higher ground, a jet of water will be forced out, if not so
high, the well will only partly fill, and so on. Artesian wells are
sunk or bored by means of instruments screwing on to the end of a set
of iron rods each screwing into the end of the other as shown in fig.
4. The first piece is generally a sort of gouge (_a_) two or three
inches wide, and so made as to bring up a cylindrical piece of earth
when forced in and screwed round, the weight of the rods after a few
pieces are added is sufficient to force the gouge into the earth,
except in stony places, when a sort of “pick” is used.
The official report of General Desvaux on the artesian borings
executed in the Desert of Zahara of the province of Constantine,
in 1856-7, states, “that a spring affording 4010 quarts of water
per minute, was the result of one of the borings, and that others
affording 35, 120, and 4,300 quarts respectively were successively
completed.” And he goes on to say: “When the shouts of the soldiers
announced the gush, the Arabs sprang in crowds to the spot, laving
themselves in the welcome abundance, into which mothers dipped their
children; while the old Sheik fell upon his knees and wept, returning
thanks to Allah and the French. At Oum Thiour a well sunk to the
depth of 170 metres and yielding 180 quarts a minute was at once
taken as the centre of a settlement by a portion of a previously
nomadic tribe.... As soon as the water appeared they began the
construction of a village, the plantation of 1,200 date trees,
and entirely renounced their wandering existence.”
According to General Desvaux’s report, these artesian wells are
likely to have a most important influence on Arab life, and greatly
to subdue the roving propensities of many of the tribes.