"The savage feels, and acting by the impression of what he feels, instead of fixing his habitation on the exposed bank of large rivers, unsheltered heights, or grounds newly cleared of their woods, seeks the cover of the forests, even avoids the streams of air which proceed from rivers, from the surface of ponds, or from lands newly opened to the sun. The rule of the savage is a rule of experience, founded in truth, and applicable to the encampment of troops, even of civilized Europeans. "In accordance with this principle, it is almost uniformly true, _cæteris paribus_, that diseases are more common, at least more violent, in broken, irregular, and hilly countries, where the temperature is liable to sudden changes, and where blasts descend with fury from the mountains, than in large and extensive inclined plains, under the action of equal and gentle breezes only. From this fact, it becomes an object of the first consideration, in choosing ground for encampments, to guard against the impression of strong winds, on their own account, independently of their proceeding from swamps, rivers, and noxious soils. "In countries covered with woods, abundantly supplied with straw, and other materials applicable to the purpose of forming shelter, it is, upon the whole, better to raise huts and construct bowers than to carry canvas. The individual is exercised by labor, and as his mind is employed in contriving and executing something for self-accommodation, he is furnished with a daily opportunity of renewing the pleasure. The mode of hutting, here recommended, effectually precludes the evils arising from those contaminations of air in which contagion is generated--an evil which often arises in tents, and is carried about with an army in all its movements in the field." * * * * * The view of the ancients in regard to the encampment of troops may be understood from the counsel of Vegetius: "Ne aridis et sine opacitate arborum campis, aut collibus ne sine tentoriis æstate milites commorentur." VI. As we have remarked before, the site of the prison was covered with trees when its outlines were traced and surveyed by the rebel engineers. These trees, felled to the ground, were hewn, and matched so well on the inner line of the palisades as to give no glimpse of the outer world across the space of the dead line, which averaged nineteen feet in width, and which was defined by a frail wooden railing about three feet in height, from fifteen to twenty-five feet distant from the palisades. [Illustration]