takes place, according to the quantity of vapour
concentrated, according to the resulting increase
of its specific gravity, it is converted into cloud,
fog, or rain.

Dew also depends on the cooling of the air,
only however to a moderate degree, and during
the night. The dew on plants is partly derived
from the moisture which they have themselves
exhaled. If a waterproof cloth is laid on a
grass plot, it will receive much less dew than
the grass does. Experiment also shows that
dew contains salts and extractive matters which
have been supplied by vegetable exhalation.

If, when atmospheric vapour is collected in
clouds, the temperature drops below the freezing
point, minute crystals of ice are formed
which, adhering together, form flakes of snow.
Hoar-frost is dew frozen as it forms. At very
low temperatures, ice is dry, and may be reduced
to an impalpable powder.

M. Monge thus explains the formation of
hail, which is confined to temperate climates.
Vapour is condensed into drops of water at a
very considerable elevation in the air. These
drops fall with the accelerated velocity impressed
upon them by the laws of motion; and as their
surface evaporates in direct proportion to that
velocity, and at the expense of the heat they
contain, their centre, cooled to zero, freezes.
The hailstones, still falling, cool still further,
and, passing through clouds, freeze the watery
particles which there attach themselves to their
surface, forming coats of greater or less thickness,
and increasing their size, sometimes very
considerably, as we occasionally experience to
our cost. Towards the close of the summer of
1834, I saw the city of Padua unroofed by a
hailstorm. On breaking a hailstone, these coats
are quite perceptible, while the primitive nucleus
sometimes affects a crystalline form.

The efficacy of mineral springs on the human
economy, and especially the different effects of
different springs, have scarcely been accounted
for by chemical analysis. Courses of treatment
by " the waters" are, therefore, in great
measure empirical. Dr. Scoutetten has lately
suggested (at the Académie Impériale de Médecine)
one cause of their activity. Mineral waters
contain no free electricity; but numerous
experiments have proved that they give
unequivocal indications of electro-magnetism. Whilst
river, spring, and lake waters are electro-magnetised
positively, mineral waters are always
negative, whether they be hot or cold. There
is no exception to the rule. If mineral water
in a porous vessel be plunged in ordinary water
contained in a second vessel concentric with the
first, a pile is obtained, and the galvanometer
put in contact with the two poles, immediately
betrays the passage of the current.

Another doctor, residing at Metz, proposes
to substitute for mineral waters a much more
attractive class of fluids. He has written a
pamphlet to prove that a real natural mineral
liquid, as active and even more charged with
mineral principles than many justly-esteemed
springs, and containing potash, soda, lime,
magnesia, iron, manganese, chlorides, sulphates,
carbonates, phosphates, is furnished by—the
juice of the grape in the form, which Noah
bequeathed to us, of wine.

Without insisting on Pindar's opinion touching
the aristocracy of water, there is room for
a few words respecting its pharmaceutical
virtues. Dr. Clochard, of Rocheserviere, advises
gargling with cold water as a new and simple
remedy for angina of the throat. As to hydropathy
in general, it suffices to allude to it.
Patrocles, at the siege of Troy, washed his
friend Euripilus's wound with water, after
drawing out the dart. It is in warfare especially
that the extreme value of water is felt. On the
field of battle, the grand active agents are
powder and steel to kill, and water to save. If
water could be had in sufficiency there, it might
save almost as many wounded as powder and
steel kill. Apart from the assuaging of burning
thirst, its external application is most beneficial.

Sydenham used to say that he would give up
medicine, if opium were taken from him;
Gassicourl said that he would renounce army
surgery, if he were forbidden the use of water.
With six or eight thousand wounded to attend
to, where could an adequate supply of balsams,
balms, and essences be found? How often have
the waters of the Rhine, the Elbe, and the
Danube, worked wonders in curing wounded
French soldiers! The great Larrey, in a printed
circular, advised his colleagues in the Grande
Armée, of every rank, to abstain from alcoholic
liquids in the dressing of gunshot wounds. In
Egypt, he proved the great advantages of the
surgical employment of water. The Nile alone
enabled him to cure the most terrible wounds.
Well might the ancients call it the river of
abundance and health!

Hydrology is an inexhaustible subject. Water
is useful when it rises—take only the
phenomena of capillarity; useful when it falls to
its horizontal position—witness its employment
in levelling. It petrifies and preserves objects
in a bed of stone. It eats away and deposits
rocks. It hollows out and garnishes caves.
Happily such waters do not convert the entrails
of those who drink them (as was once believed)
into concrete and plaster. Water works most
of the changes on the surface of the globe,
lowering hills, raising valleys, filling up estuaries,
creating deltas at the mouths of rivers,
undermining cliffs, and preparing even the bed of the
sea for the use of living creatures at its first
uprising. Water has been turned aside from its
beneficial uses to aid in ordeals and torturing.
In the clepsydra it measures time; in the ceaseless
flow of rivers it figures eternity; while, in
the tides, it is a type of perodicity and reciprocity.

So useful and well-known a thing as water
necessarily lends itself to popular and figurative
phraseology. When an argument won't hold
water, it shows want of tact to press it too
close. As we have fresh-water sailors, so the
French have their " fresh-water doctors "—the
one held in equal honour with the other—