VENTILATH )N, the method of supplying buildings with fresh air. In buildings which are intended for habitation, or where large bodies of persons are at any tune to be eon gregated it is requisite that there should be some means of replenishing the apartment with a constant supply of pure air. This necessity arises from the fact, that air, when once parsed the hunnm system, is unfit for re-inspiration, that portion which is emitted being not only useless, but deleterious to health. On this account it becomes necessary to remove this vitiated air, and to substitute fresh air, which should be at a temperature of about to The viti ated air, on being emitted from the mouth, has a temperature between and and being thereby ratified and rendered lighter, has a tendency to rise to the upper part of the apart ment. The method hereby naturally suggested for its removal is the provision of some means of escape at the top of the apartment; the success of this method, however, would be nullified, it' the heated air, on emerging from the top of the room into a shaft intended to conduct it away, were to meet with a current (ut' cold air, and it is therefore fund necessary to heat the air in the shaft, so as to assist the upward draft.
It is further necessary to keep up a eonstant supply of fresh air to take the place of the foul air as it is removed ; this is necessary, not only fie: the purposes of health, but also to preserve the upward draft. In solve instances, means have been adopted forcing fresh air in with fans or bellows; but this is scarcely necessary, for if the fresh air be only allowed admission into the apartment, it will naturally enter to full up the vacuum caused by the dispersion of the ftml air. These methods, however, are seldom adopted together; some times the shaft, and at others the him, is employed. Some persons Colltend, that the method of heating the air in the shaft does not answer the intended object, but rather causes a downward current. In supplying fresh air. it is to be observed, that cold currents of air arc to be avoided : it is sometimes customary to heat the air to a certain temperature before admitting it into the apartment. the temperature being regulated according to the season of the year.
V ENTILATon, (fonn the Latin. yenta°, to fan,) machine made to turn with the wind, and placed in the wall or roof, in order to throw a due quantity of fresh air into a close apartment.