VENTILATOR

, a machine by which the noxious air of any close place, as an hospital, gaol, ship, chamber, &c, may be discharged and changed for fresh air.

The noxious qualities of bad air have been long known; and Dr. Hales and others have taken great pains to point out the mischiefs arising from foul air, and to prevent o<*> remedy them. That philosopher proposed an easy and effectual one, by the use of his Ventilators; the account of which was read before the Royal Society in May 1741; and a farther account of it may be seen in his Description of Ventilators, printed at London in 8vo, 1743; and still farther in part 2, p. 32, printed in 1758; where the uses and applications of them are pointed out for ships, and prisons, &c. For what is said of the foul air of ships may be applied to that of gaols, mines, workhouses, hospitals, barraeks, &c. In mines, Ventilators may guard against the suffocations, and other terrible accidents arising from damps. The air of gaols has often proved infectious; and we had a fatal proof of this, by the accident that happened some years since at the Old Bailey sessions. After that, Ventilators were used in the prison, which were worked by a small windmill, placed on the top of Newgate; and the prison became more healthy.

Dr. Hales farther suggests, that Ventilators might be of use in making salt; for which purpose there should be a stream of water to work them; or they might be worked by a windmill, and the brine should be in long narrow canals, covered with boards of canvas, about a foot above the surface of the brine, to confine the stream of air, so as to make it act upon the surface of the brine, and carry off the water in vapours. Thus it might be reduced to a dry salt, with a saving of fuel, in winter and summer, or in rainy weather, or any state of the air whatever. Ventilators, he apprehends, might also serve for drying linen hung in low, long, narrow galleries, especially in damp or rainy weather, and also in drying woollen cloths, after they are fulled or dyed; and in this case, the Ventilators might be worked by the fulling water-mill. Ventilators might also be an useful appendage to malt and hop kilns; and the same author is farther of opinion, that a ventilation of warm dry air from the adjoining stove, with a cautious hand, might be of service to trees and plants in green-houses; where it is well known that air full of the rancid vapours which perspire from the plants, is very unkindly to them, as well as the vapours from human bodies are to men: for fresh air is as necessary to the healthy state of vegetables, as of animals.—Ventilators are also of excellent use for drying corn, hopsand malt.—Gunpowder may be thoroughly dried, by blowing air up through it by means of Ventilators; which is of great advantage to the strength of it. These Ventilators, even the smaller ones, will also serve to purify most easily, and effectually, the bad air of a ship's well, before a person is sent down into it, by blowing air through a trunk, reaching near the bottom of it. And in a similar manner may stinking water, and ill tasted milk, &c, be sweetened, viz, by passing a current of air through them, from bottom to top, which will carry the offensive particles along with it.

For these and other uses to which they might be applied, as well as for a particular account of the construction and disposition of Ventilators in ships, hospitals, prisons, &c, and the benefits attending them, see Hales's Treatise on Ventilators, part 2 passim; and the Philos. Trans. vol. 49, p. 332.

The method of drawing off air from ships by means of sire-pipes, which some have preferred to Ventilators, was published by Sir Robert Moray in the Philos. Trans. for 1665. These are metal pipes, about 2 1/2 inches diameter, one of which reaches from the fireplace to the well of the ship, and other three branches go to other parts of the ship; the stove hole and ash hole being closed up, the fire is supplied with air through these pipes. The defects of these, compared with Ventilators, are particularly examined by Dr. Hales, ubi supra, p. 113.

In the latter part of the year 1741, M. Triewald, military architect to the king of Sweden, informed the secretary to the Royal Society, that he had in the preceding spring invented a machine for the use of ships of war, to draw out the foul air from under their decks, which exhausted 36172 cubic feet of air in an hour, or at the rate of 21732 tuns in 24 hours. In 1742 he sent one of these to France, which was approved of by the Academy of Sciences at Paris, and the navy of France was ordered to be furnished with the like Ventilators.

Mr. Erasmus King proposed to have Ventilators worked by the fire engines, in mines. And Mr. Fitzgerald has suggested an improved method of doing this, which he has also illustrated by figures. See Philos. Trans. vol. 50, p, 727.

There are various ways of Ventilation, or changing the air of rooms. Mr. Tidd contrived to admit fresh air into a room, by taking out the middle upper sash pane of glass, and fixing in its place a frame box, with a round hole in its middle, about 6 or 7 inches diameter; in which hole are fixed, behind each other, a set of sails of very thin broad copper-plates, which spread over and cover the circular hole, so as to make the air which enters the room, and turning round these sails, to spread round in thin sheets sideways; and so not to incommode persons, by blowing directly upon them, as it would do if it were not hindered by the sails.

This method however is very unseemly and disagreeable in good rooms: and therefore, instead of it, the late ingenious Mr. John Whitehurst substituted another; which was, to open a small square or rectanglar hole in the party wall of the room, in the upper part near the cieling, at a corner or part distant from the | fire; and before it he placed a thin piece of metal or pasteboard &c, attached to the wall in its lower part just below the hole, but declining from it upwards, so as to give the air, that enters by the hole, a direction upwards against the cieling, along which it sweeps and disperses itself through the room, without blowing in a current against any person. This method is very useful to cure smoky chimneys, by thus admitting conveniently fresh air. A picture placed before the hole prevents the sight of it from disfiguring the room. This, and many other methods of Ventilating, he meant to have published, and was occupied upon, when death put an end to his useful labours. These have since been published, viz in 1794, 4to, by Dr. Willan.