II. INGRESS AND EGRESS OF AIR.—Though windows, especially when made to open above, afford a very convenient means for the ingress and egress of air, they should not be the sole resources for ventilation in any apartment in new buildings, especially where gas-lights, or any other powerful and brilliant lamps are used, or where they are likely to be crowded with visitors. An aperture in the ceiling of every apartment, constantly drawing off vitiated air, is the great desideratum. It should communicate with a flue discharging into the external air, and be protected there from local currents, or down-draughts, arising from the action of the wind. Valves should regulate with precision the amount of discharge, and arrest it entirely when they are closed. An aperture near the ceiling in an ordinary chimney is sometimes sufficient, but it cannot always be trusted. An independent discharge is better. The ingress of air should be equally under control, and supply air where it can enter gently, and diffuse itself most widely, without local draughts, through the apartment to be ventilated.
A very important arrangement has been introduced in numerous buildings, which consists in providing a large aperture above all internal doors leading to individual rooms, while valves regulate the amount of clear opening permitted. The staircase and passages being constantly supplied with a mild atmosphere, such rooms can always be ventilated from this source, the aperture admitting fresh air and discharging vitiated air by the general discharge from the upper part of the staircase. There, too, the principal ingress, as well as the channel for the escape of vitiated air, is constructed so that the cold air, as it enters, receives indirectly some warmth from the vitiated air. In large assemblies, and where apartments are crowded, it is desirable to maintain a more perfect separation between the fresh and the vitiated air, so as to facilitate the ingress of the former, and the escape of the latter.
Where a more complete system of ventilation is desired, nothing conduces more to secure this object in individual habitations than the construction of a special flue for the discharge of vitiated air. A connection can be established at any time between it and individual rooms, closets, or cellars, and all vitiated air expelled with a velocity proportional to the amount of fuel consumed in this flue.
Thus, then, in the habitations of the people, the independent warming and ventilation of each individual room is the first object; whatever system of heating be employed. The warming of the whole house, to a certain extent at least, through the hall, passage, or staircase, is another desideratum. The special action of a ven-
tilating flue, available at all times and seasons on one or more rooms, is a luxury that has hitherto been only rarely introduced in private dwellings.