In the centre of the cylinder, there is now put (perpendicularly) a shaft, of about three inches diameter and of the length of the cylinder; and having it, and the centres of the top and bottom of the cylinder, so prepared and fitted to each other, that the shaft may easily turn round, or revolve; then there are fixed on it, at right angles to each other, eight arms or radii, four at top, and four at bottom; the bottom four being' exactly under the upper ones. To these arms there are fixed four sheets, or pieces of iron plate, of such lengths and widths as will just go into, and fill up, (though without touching,) the space left between the shaft and the side of the cylinder; and these things being so done, that the plates or leaves fixed on the arms may turn easily round, inside the cylinder; and the ends and sides of these leaves being so fitted to each other that, when the leaves are turned round, there may not be a space greater than about the sixteenth of an inch left between them, the arrangements for the door-way are complete; and the cylinder through which the place is entered, has within it four leaves or wings, somewhat like the fans of a winnowing-machine, fixed perpendicularly.

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Now, the effect of these arrangements is this: - Were a common door to be made use of, whenever it was opened, freeingress or egress would be given to air, and it would pass from, or into the place, as circumstances dictated. But with a door arranged in this way, no air can at any time pass either into, or out of the place, excepting by the narrow space or crevice left between the edges of the leaves and the inside of the cylinder; since, the leaves being all at right angles with each other, and the two apertures in the cylinder being neither of them so wide as to be equal to ninety degrees of a circle of the same diameter as this door-way cylinder, it follows that, turn, or cause the leaves to revolve in what way we may, two of them will always be within the uncut parts of the cylinder, and constantly interposed between the inside of the place and the open air; and in consequence, there never can be any other passage for air into, or out of the place, by thisdoor-way, than by the space or crevice between the edges of the leaves, and the inside of the cylinder.

When the windows and door are thus finished, I proceed as follows with the ventilator: - To the aperture in the ceiling, through which ventilation takes place, there is fixed a pipe of an equal diameter with that aperture; which pipe goes through the roof and then descends, and opens into a reservoir or cistern, situated on the outside of the building. Now, with things thus arranged, and with the cistern so far filled with water that the end of the ventilation-pipe is immersed a few inches in the water, the machinery by which the warm air is injected is set to work, when air, fresh, andof a temperature pleasantto the feelings, is injected into the bottom of the building, at a rate sufficient for the consumption of the people inside. ' The pipes which convey this air, are so contrived and arranged, as to distribute it over the whole surface of the floor, in a way which renders its introduction imperceptible; and consequently inconvenience from drafts or currents of it is guarded against. As fast as it is distributed over the floor, it gives place to the air that follows it, and rises towards the ventilator.

In its ascent it passes the persons of the people in the place; and becoming, from the heat imparted to it by their bodies, and from the deteriorating effects of their respiration, lighter, it rises more rapidly towards the ventilator.

Now, from the arrangements and lutings I have mentioned, the only places where this air can find egress, are through the ventilation-pipe, and by the spaces or crevices between the door-way cylinder, and the leaves that revolve in it; and these spaces or crevices being, when the cylinder and leaves are well finished and fitted to each other, as almost nothing in comparison with the quantity of air injected, it follows that the ventilation-pipe must be the main channel of exit. But before any air can pass through this pipe, it must displace the water inside that end of it which is immersed in the cistern; to displace this, a slight pressure must be thrown upon it; the causing this pressure will somewhat condense the air in the ventilation-pipe; and as this condensation will, owing to that principle of fluids by which action and reaction are communicated, be reverted, or reflected back upon, and caused to take place with respect to all the air in the building, the whole of it will be somewhat condensed, and, in consequence, the building will have in it a quantity of air greater than it would under common circumstances have, according to the depth to which the end of the ventilation-pipe is immersed in the water.

Now, as this compressed state of the air, and the building's thus having within it more than it would under common circumstances contain, is contrary to the natural tendencies of air, its expansive principle will be exerted, and every crack and crevice about the place will become a channel to let air out instead of into it; and, in consequence, drafts into the building effectually prevented, owing to every cranny through which they used to enter, becoming a channel of egress instead of ingress.

This is the way in which I prevent and do away with "drafts;" and when the door and ventilation apparatus (which is, in fact, nothingmore than a most sensitive valve, and to which a valve would, under some circumstances, be preferable.) are well arranged, and their effect not counteracted by any of the cracks and crevices which are about rooms being suffered to remain unluted, or otherwise unstopped, the evil it is intended to remedy will be effectually done away with.

There is, to be sure, both singularity, and a degree of inconvenience, in a door-way such as I have described; though, by having the panels of the revolving-leaves of glass, this might be much done away with; and as there is no other equally convenient way of preventing all possibility of annoyance from the door, whenever any one either entered or went out of the place, it might be submitted to, should common doors not be considered sufficient.

With the prevention of inconvenience, and the danger of taking cold inside the building, would also be the removal of much of the liability to cold, etc, when leaving the now highly heated atmospheres of public places; as, owing to the temperatures being always uniform, and never above that which was agreeable and salubrious, much of the danger we all experience, and many of the indispositions people of delicate constitutions incur, in consequence of passing from those atmospheres to the open air, would be done away with. And, by varying the depth of the water, in which the ventilation-pipe is immersed, according to the variations of the barometer, constant uniformity, as to the density of the atmosphere inside of the building, might be maintained."

The usual mode of ventilating ships is by a canvass bag, called a wind-sail. This is suspended over the principal aperture in the deck, and having an opening in the direction of the wind, a current is propelled downwards, which tends to purify the air. But ventilation is chiefly required in ships during foul weather, when such a process as that of the wind-sail cannot possibly be employed. Mr. Jacob Perkins has proposed, under these circumstances, the following very simple arrangement.

a and b represent two casks or tanks half filled with water, placed on the opposite sides of the vessel, with a channel c, having an open communication with both; d and e represent two large hoses or pipes, through which the foul air from below deck escapes into the tank, where there are valves opening inward; fand g are two pipes furnished with valves opening outwards, serving to discharge the foul air out of the tanks. Now, when the tank a is elevated by the ship's motion, the water will run along the pipe c into the depressed tank b, the rising of the water in which will open the valve of the pipe g, and discharge as much air as the water displaces. At the same time the elevated tank a is receiving the foul air from below through the hose d, the valve in it having been opened by the pressure acting upon the vacuum formed in a by the retiring of the water, the external pressure of the atmosphere having shut the valve in the discharge-pipe f: now, when the vessel rocks in the opposite direction, as would be represented by a line from d to g, the charge of foul air in the tank a, is discharged by its filling with water in the manner already shown as respects the tank b; and thus the operation is continually performed by the oscillation of the vessel.

It will, however, be evident that, if the tanks be fixed at right angles to the keel, the ventilation will only be effected by the rolling of the ship: but if the tanks be placed diagonally, then the ventilation will be equally effected by the pitching also. A very excellent warming and ventilating stove for buildings, particularly adapted to manufactories, by the same ingenious mechanician, is described under the article Air: which see.

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