ix million gallons a day,
and, in 1851, at nearly double that amount, the increase being
accompanied by an average fall of no less than two feet a year in the
level to which the water rose. The water stood commonly, in 1822, at
high-water mark, and had sunk in 1851 to 45, and in some wells to 65
feet below high-water mark.[307] This fact shows the limited capacity of
the subterranean reservoir. In the last of three wells bored through the
chalk at Tours, to the depth of several hundred feet, the water rose 32
feet above the level of the soil, and the discharge amounted to 300
cubic yards of water every twenty-four hours.[308]

By way of experiment, the sinking of a well was commenced at Paris in
1834, which had reached, in November, 1839, a depth of more than 1600
English feet, and yet no water ascended to the surface. The government
were persuaded by M. Arago to persevere, if necessary, to the depth of
more than 2000 feet; but when they had descended above 1800 English feet
below the surface, the water rose through the tube (which was about ten
inches in diameter), so as to discharge half a million of gallons of
limpid water every twenty-four hours. The temperature of the water
increased at the rate of 1.8 degrees F. for every 101 English feet, as
they went down, the result agreeing very closely with the anticipations
of the scientific advisers of this most spirited undertaking.

Mr. Briggs, the British consul in Egypt, obtained water between Cairo
and Suez, in a calcareous sand, at the depth of thirty feet; but it did
not rise in the well.[309] But other borings in the same desert, of
variable depth, between 50 and 300 feet, and which passed through
alternations of sand, clay, and siliceous rock, yielded water at the
surface.[310]

The rise and overflow of the water in Artesian wells is generally
referred, and apparently with reason, to the same principle as the play
of an artificial fountain. Let the porous stratum or set of strata, _a_
_a_, rest on the impermeable rock _d_, and be covered by another mass of
an impermeable nature. The whole mass _a_ _a_ may easily, in such a
position, become saturated with water, which may descend from its higher
and exposed parts--a hilly region to which clouds are attracted, and
where rain falls in abundance. Suppose that at some point, as at _b_, an
opening be made, which gives a free passage upwards to the waters
confined in _a_ _a_, at so low a level that they are subjected to