The act of renovating the air of chambers, houses, ships, and all kinds of buildings or places. We may exist for several days without food, but we die, if deprived only for a few minutes of air. As air is necessary to life, so is pure air to health. But it appears that this important fact escapes the attention of the greater part of mankind, who are prone to blame the cook or the purveyor for the greater part of their ailments, without reflecting upon the impure air they may have been inspiring at the rate of about two gallons per minute. The oxygen gas, or vital portion of the atmosphere that enters the lungs, is changed at each respiration into carbonic acid gas. This gas, as is well known, is poisonous, if inspired alone, or even if a large proportion of it be mixed with the atmospheric air. But by an admirable provision of the great Author of Nature, this contaminated air is rendered specifically lighter than the pure atmosphere, from the heat it has derived from the lungs, and consequently rises above our heads, during the short pause between our respirations; thus insuring to us always a pure draught of air, unless we prevent it by artificial means.

It is not, however, always owing to a deficiency of oxygen, that the air of rooms or crowded places becomes pernicious to health. A council of health, established by the French government, proved that in an atmosphere which had not lost one-twentieth part of its oxygen, an animal miasmata was diffused in vapoure; that by suspending, in such atmospheres, a glass vessel filled with ice, the vapour diffused in the air becomes condensed on its surface, and the liquid thus obtained by condensation, being collected in another vessel suspended underneath the former, exhales a fetid odour, and speedily undergoes the putrid fermentation, when exposed to a temperature of 79° Fahr.

Certain gaseous and other vapours may be mixed with the air we breathe, without producing any very marked inconvenience; but the effects of a mixture of many other kinds are highly dangerous, and more quick in their action than even those of animal miasmata. A constant renewal of the air is absolutely necessary for its purity; for in all situations, it is suffering either by its vital part being absorbed, or by impure vapours being disengaged and dispersed through it. Ventilation therefore resolves itself into the securing a constant supply of fresh air. Rooms cannot be well ventilated, that have no outlet for the air, and this, from the superior levity of foul air, should be made at the highest point that can be obtained, and so arranged as to diffuse the fresh air that enters over the upper part of the room, and not inconvenience the persons in the room, by descending upon them in a current. There should be a chimney to every room, which on no account should be stopped up with a chimney-board, as is often the case in bed-rooms. We have observed also, in many houses, that the top sashes of windows of the upper rooms are made fast; now if these were made to slide downward, instead of the lower sashes upward, increased salubrity, as well as security, (especially in the case of children,) would be obtained.

In whatever way fresh air may be made to enter an apartment, it should be, as far as may be practicable, at the part remotest from the fire-place, in order that it may traverse the whole apartment in its passage to the chimney. The most effective species of ventilation is that in which nature is adopted as the guide. The simple action of the sun, no less than the devastating phenomenon of the African tornado, tend to the same result. We have only to change the temperature of the air which surrounds us, and a new portion will rush in from the adjacent and purer parts, to supply its place. From this it is obvious, that a lamp placed in an aperture of the ceiling, in any large and crowded room, will tend to purify the air. This is precisely the case in our large theatres, as that at Covent Garden, where the great glass chandelier, with its numerous gas-burners, gives out a great quantity of heat, immediately under a large funnel, which passes through the roof, into the open air. The rarified air which thus rushes through the funnel, is constantly succeeded by continuous fresh currents, entering at numerous apertures beneath, to restore the equilibrium of pressure.

Notwithstanding this arrangement is calculated to render the atmosphere of crowded places more fit for respiration, it is productive of a painful and serious inconvenience to those persons who may be situated near to the apertures before-mentioned, where the fresh air enters; they are thus exposed, as it were, to the action of a series of blow-pipes, and the consequences are, colds, asthmas, and rheumatisms, in abundance. To avoid drafts, and yet ventilate thoroughly, has hitherto been found of difficult accomplishment. In " A letter to the Earl of Chichester, on the practicability of rendering those properties of air, which relate to caloric, applicable to new and important purposes, (1823,)" by Mr. John Vallance, of Brighton; that gentleman has proposed a plan for warming and ventilating the Houses of Parliament, which, in principle, is admirably designed to obviate the difficulties just mentioned; we shall, therefore, give it a place here in the author's own words; although there are some mechanical difficulties to be overcome, before it can be rendered elegant and convenient; the means of effecting which, will, we trust, be ultimately accomplished.

"There are two principles which operate to alter the state of air, in any place where numbers of people convene. One of them affects it physically, and to a change of density, and is the cause of drafts and influxes of cold air; the other affects its chemically, and to a change of quality, as the medium by which the action of the lungs is rendered efficient to the preservation of life, and renders necessary, and indeed indispensable, the drafts and currents of which the first is the cause. The first of these occurs in every place in which air is heated; the other, only in those places in which it undergoes respiration. Now, it is the first only of these that falls under our consideration, when investigating the principle on which drafts take place; and the course of operation of this principle is thus. If heat be communicated to a particle of air, a change takes place with respect to that particle in the following manner; it becomes expanded and increased in bulk, in some such way as may be conceived, by reference to the juvenile practice of holding a flaccid bladder before the fire, to tighten and fill it up again, prior to using it as a football.