t regularly ebb
and flow.

If the transmission of water through a porous medium be so rapid, we
cannot be surprised that springs should be thrown out on the side of a
hill, where the upper set of strata consist of chalk, sand, or other
permeable substances, while the subjacent are composed of clay or other
retentive soils. The only difficulty, indeed, is to explain why the
water does not ooze out everywhere along the line of junction of the two
formations, so as to form one continuous land-soak, instead of a few
springs only, and these far distant from each other. The principal cause
of this concentration of the waters at a few points is, first, the
frequency of rents and fissures, which act as natural drains; secondly,
the existence of inequalities in the upper surface of the impermeable
stratum, which lead the water, as valleys do on the external surface of
a country, into certain low levels and channels.

That the generality of springs owe their supply to the atmosphere is
evident from this, that they become languid, or entirely cease to flow,
after long droughts, and are again replenished after a continuance of
rain. Many of them are probably indebted for the constancy and
uniformity of their volume to the great extent of the subterranean
reservoirs with which they communicate, and the time required for these
to empty themselves by percolation. Such a gradual and regulated
discharge is exhibited, though in a less perfect degree, in every great
lake which is not sensibly affected in its level by sudden showers, but
only slightly raised; so that its channel of efflux, instead of being
swollen suddenly like the bed of a torrent, is enabled to carry off the
surplus water gradually.

Much light has been thrown, of late years, on the theory of springs, by
the boring of what are called by the French "Artesian wells," because
the method has long been known and practised in Artois; and it is now
demonstrated that there are sheets, and in some places currents of fresh
water, at various depths in the earth. The instrument employed in
excavating these wells is a large augur, and the cavity bored is usually
from three to four inches in diameter. If a hard rock is met with, it is
first triturated by an iron rod, and the materials being thus reduced to
small fragments or powder, are readily extracted. To hinder the sides of
the well from falling in, as also to prevent the spreading of the
ascending water in the surrounding soil