“The heated air is always admitted near the ceiling to obviate any contamination at its point of delivery. The foul air is drawn off near the wash-board, any impurities there deposited being drawn down, but not into the room. The diffusion of the air, where an adequate exhaustive power is provided, is also much favored by being thus turned in its course, and the lower stratum is not uncomfortably cool to the feet,--a common objection to the usual method of receiving and withdrawing the supplies. “The foul air channels into which the flues from each story open, do not come together, until just as they pass under the foot of the ventilating shaft or chimney, which through the agency of a cast iron pipe, a foot in diameter in the middle of the shaft, running up fifty feet and receiving the smoke from the furnaces, constitutes the moving power. This shaft is built of brick in a useless angle where the two buildings approached each other, and has an internal diameter, it being a circle, of about six feet at its basis a few feet below the cellar floor, and terminates in one of the original chimney stacks at the corner of the foundation of the dome, height of about seventy-five feet, and with about one half its size at bottom. A deviation of a few feet from the perpendicular was inevitable at about two-thirds its length. It is carefully plastered or _pargetted_ within. As its upper opening was commanded by the spherical dome, endangering the regurgitation of wind at certain times, it was surmounted with a form of chimney-cap, figured in Mr. Tredgold’s works some forty years since, and being essentially that recently introduced into considerable use in this vicinity. “As a cure for smoky chimneys, this cap has considerable efficiency, but is regarded as of very trifling moment as for as suction or exhaustion from below is required. For its power is too feeble at all times, for such an amount of ventilation as an insane hospital requires, and depends wholly on the fluctuation currents of external air. If the upper range of bricks had been laid with a bevel upwards, and a plain plate of metal placed on four short legs a few inches above, it would have answered equally well and at a tenth of the cost. The rarefaction produced by the heat radiated from the central iron smoke pipe occasions a partial vacuum, instantly filled from the rooms behind.