e beautiful waters of the Dee, and numberless other rivers
that flow through the hollow of every valley. Switzerland has long been
celebrated for the purity and excellence of its waters, which pour in
copious streams from the mountains, and give rise to the finest rivers
in Europe.

Some rivers, however, that do not take their rise from a rocky soil, and
are indeed at first considerably charged with foreign matter, during a
long course, even over a richly cultivated plain, become remarkably pure
as to saline contents; but often fouled with mud containing much animal
and vegetable matter, which are rather suspended than held in true
solution. Such is the water of the river Thames, which, taken up at
London at low water mark, is very soft and good; and, after rest, it
contains but a very small portion of any thing that could prove
pernicious, or impede any manufacture. It is also excellently fitted for
sea-store; but it then undergoes a remarkable spontaneous change, when
preserved in wooden casks. No water carried to sea becomes putrid sooner
than that of the Thames. But the mode now adopted in the navy of
substituting iron tanks for wooden casks, tends greatly to obviate this
disadvantage.

Whoever will consider the situation of the Thames, and the immense
population along its banks for so many miles, must at once perceive the
prodigious accumulation of animal matters of all kinds, which by means
of the common sewers constantly make their way into it. These matters
are, no doubt, in part the cause of the putrefaction which it is well
known to undergo at sea, and of the carburetted and sulphuretted
hydrogen gases which are evolved from it. When a wooden cask is opened,
after being kept a month or two, a quantity of carburetted and
sulphuretted hydrogen escapes, and the water is so black and offensive
as scarcely to be borne. Upon racking it off, however, into large
earthen vessels, and exposing it to the air, it gradually deposits a
quantity of black slimy mud, becomes clear as crystal, and remarkably
sweet and palatable.

It might, at first sight, be expected that the water of the Thames,
after having received all the contents of the sewers, drains, and water
courses, of a large town, should acquire thereby such impregnation with
foreign matters, as to become very impure; but it appears, from the most
accurate experiments that have been made, that those kinds of impurities
have no perceptible influence on the salubri