III. EQUALIZATION.—Air entering by doors, windows, or other apertures, and rushing in a well defined but partial stream, so as to produce local currents, may be exceedingly offensive, while, if divided into innumerable smaller streams, by causing it to pass through a porous texture having the most extensive possible surface, it may proceed so gently as not to be perceived. Air ought always to be admitted in this manner, or at such a distance from those upon whom it is to act, that its impulse may be greatly moderated before it reaches them. Wherever a proper supply of air is admitted, this equalization is essential, more particularly in crowded apartments; and the greater the degree to which it is carried, the more perfect and agreeable is the result. Nothing is more common than to see apartments ventilated effectually, so far as may be necessary for the removal of foul air, but with a movement that induces a most offensive series of chilling draughts, if means be not taken to warm the supply of air given, and for introducing an effective equalization. In rooms for invalids, this subject becomes of great consequence, especially in diseases of the chest. To a great number of constitutions, unequal currents are as dangerous and offensive as an oppressive atmosphere.