ed with
Wood, where there is no free Circulation of Air. However, it ought to
be observed, that it is not the Neighbourhood of Water alone which is
prejudicial, but the watery Vapours which keep the Air perpetually
moist, and the Exhalations of corrupt Effluvia, which render such
Places unwholesome; for the Neighbourhood of Rivers, and of the Sea,
where the Tide ebbs and flows freely, has no such Effect, where the
Situation is dry and airy; and those very unhealthy marshy Grounds
often continue healthy in cold Weather, when their Waters are
refreshed with Rains[136], and little or no moist putrid Exhalations
rise from them; though, as Dr. _Pringle_ observes, in Summer and
Autumn, when their Waters begin to corrupt, and the Exhalation is
strong, they are always exposed to Diseases; and it is for this
Reason that such Places are always very unhealthy in warm Climates.

[134] Mr. _du Hamel_ says, that the Air of the Island of _St.
Domingo_ is very fatal to _Europeans_; but it is observed
that those People who inhabit the rising Grounds are much
less exposed to Diseases than those who live in the Vallies.
_Sur la sante des Equipages_, art. i. p. 16.

[135] Ground may seem very dry and healthful, and yet be
quite the contrary, as Dr. _Pringle_ remarks is the Case in
the Neighbourhood of _Bois le Duc_, in _Flanders_, where
Water is found every where at the Depth of two or three Feet
from the Surface.

[136] Mr. _du Hamel_ remarks, that Places which were formerly
very subject to Diseases have become healthful when the Water
which surrounded them was refreshed by opening a
Communication with the Sea. _Ibid._ art. i. p. 18.

Hence, where the military Operations will permit, Commanders, if
possible, ought to chuse a dry Ground, whose Situation is high, and
which admits a free Current of Air, such as on the Banks of Rivers,
where there is generally a Stream of fresh Air, and Plenty of fresh
Water to supply the Camp[137]; taking Care to avoid the Neighbourhood
of low marshy Grounds, and corrupt stagnating Waters, especially in
Summer, and in hot Climates.

[137] Dr. _Pringle_ observes, that where Grounds are equally
dry, that the Camps are always most healthful on the Banks of
large Rivers; because in the hot Season Situations of this
Kind have a Stream of fresh Air from the Water, tending to
carry off both the moist and putrid Exhalations.--And in