In all Countries, and in all Climates, great Care ought to be taken in chusing the Ground on which Men are to encamp. Dry high Grounds, exposed to the Winds, where there is a free Current of Air, and which lie at a Distance from Marshes, stagnating Water, and large Woods, are generally healthful in very different Climates[134]. But Places situated low, where, on digging two or three Feet below the Surface of the Earth, you come to Water[135], and marshy Grounds, and Places surrounded with corrupt stagnating Water, are almost always the contrary, and very unhealthful; as are often those Grounds which are subject to be overflowed by large Rivers, and low Places covered 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 santé 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.