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three of these, (one to each mast), the feamen are a considerable time in getting their apparatus ready, and in hoisting them up to make use of. 2dly, They can only be used in mild weather. 3dly, Near the equator, where fresh air is most wanted, there fometimes happen such stark calms, that they are useless, by not having air enough to distend them. 4thly, The air hereby admitted passes only into the upper and more open parts of the ship, so that the well, &c. receive no change therefrom ; and it is observed, that fometimes, upon using them after some discontinuance, they drive offensive air into the cabin, and more airy parts of the ship : like as the pouring fome fresh into stinking water makes the whole link, though in a less degree. Sthly, They are improper to be used in the night-time, when the people are fleeping between decks. And lastly, admitting they had none of the former inconveniencies, their use must be destructive in hospital-thips; where, though fresh air imperceptibly received, is absolutely neceffarý to preserve the crew as free as possible from the infectious breath and exhalations of the diseased and wounded seamen ; yet blasts of wind, pouring impetuously into the very places where the sick lie, must be attended with such confequences as are too obvious to mention.
To remedy these inconveniencies, to prevent the air proving foul even in the wells and holds of ships, and to cause imperceptibly a large circulation of fresh air into every part of the ship at all times, Mr Sutton has invented the following scheme, which is useful not only in these cases, but, by altering fome parts as particular places require, may be applied to
houses, the close parts of prisons, wells at land, privies, hospitals, c.
Nothing rarefies air fo confiderably as heat, which whenever it causes a diminution in the density of the air, that part next in contact will rush in, and be fucceeded by a constant supply, till the air becomes of an equal degree of elasticity. Therefore, if a tube be laid in the well, hold, or any other part of the thip, and the upper part of this tube be sufficiently heated to rarefy the impending column of air, the aquilibrium will be maintained by the putrid air from the bottom of the tube, which being drawn out this way, a supply of fresh air from the other parts of the thip will succeed in its place ; which operation, being continued, will entirely change the air in all parts of the ship. This principle, exactly conformable to the doctrines of pneumatics, is the basis of Mr Sutton’s machine, which being put in execution on board the hulk at Deptford, before the Lords of the Admiralty, Commissioners of the Navy, our very learned and ingenious President, M. Folkes, Efq; Dr Mead, &c. performed to their fatisfaction, in bringing air from the bread-room, horlop, and well of the ship at the same time, in such quantity, that large lighted candles being put to the end of the tubes, the flame was immediately sucked out as fast as applied, though the end of one of the tubes was above twenty yards distant from the fire. The method is as follows. • To boil the provisions of the ship's company, they must have a copper, which is bigger or less, in proportion to the size of the ship, and number of the crew ; this copper is fixed in ships in the manner as
on land, having under it two openings divided by an
The first opening, baving an iron door, is for the fire ; the ashes from the grate drop through into the bottom of the other ; the smoke passes through a chimney, and is discharged as usual. After the fire is lighted, it is supported by the air from the parts next the alh-pit; but having, contrary to the usual custom, adapted an iron door, like the former, made very tight, to preverit the ingress of air, the fire would soon be extinguished, if not supplied by some other aperture : in order to which, one or more holes are made through the brick-work in the side of the ash-pit; and tubes of lead or copper, fitted closely in the holes, and made fast, are laid from thence into the well, and other parts of the ship; by which means the air next the bottom of the tubcs rushes through them, and the foul and stinking air succeeding is transmitted through the fire, and passes off, without offending, by means of the chimney; and a supply of fresh air from the other parts of the ship continually fills the place of the former, the fire requiring a constant support. This support will not be wanting, not only during the continuance of the fire, but while any warmth remains in the fire-place, copper, or brick-work, as was observed on board the hulk at Deptford, where the draught of air through the tube lasted above twelve hours after the fire was taken away.
This being considered, as the dressing the provisions for a number of people will take up fome hours every day, the warmth of the brick-work and Aues will continue a draught of air from one day to the next. Mr Sutton proposes thus to circulate the air by the fame, and
no greater expense of fire than is customarily used for the neceffities of the ship.
The operation of the machine will be equally useful in large as in small ships ; for the greater the number of people they have on board, the larger quantity and longer continuance of the fire will be necessary to dress the provisions; and therefore there will be required a greater quantity of air to support that fire. The size and number of the tubes need not be specified ; because as the circulation of air is in proportion to the quantity of fire ; the wider the tube, and greater the number of them, the less the velocity of the air, and vice versa.
I feveral times took notice in this machine, when, for the sake of observation, after the fire was well lighted, the lowest iron door was left open, that the flame did not ascend so high, or burn fo fierce ; but immediately upon shutting thereof, when the draught of air was only through the tubes, the flame foon recovered its former vigour,
There is likewise, especially in large ships, not only a copper, but also a fire grate like those used in kitchens : that the heat and smoke of this also may not be useless, an iron tube may be fixed behind the grate, and inferted quite through the brick-work, and through the deck, so that one end thereof will stand about a foot, or little more, in the chimney above the brick-work, and the other will enter into the hold, or any other part of the ship; the upper end of this tube then being heated, the draught of air will be supplied from below, as in the other case. This likewile was tried on board the hulk, with an iron tube about two inches and an half in diameter, and the
lighted candles held at the bottom of this tube were extinguished as fast as by any of the others.
It may be objected, that a number of tubes take up too much room, especially in merchant-ships, and are subject to be broken or injured by loading or unloading: to remedy which, it is adviseable, that only one tube of a convenient size be made fast unto the side of the alh-pit, and, as soon as it comes through the main deck, to compress it (a circular or any other form being equally useful) not too clofe ; and it may be divided into as many
ramifications as may
be thought necessary, (especially as the bread-room, 1tore-room, &c. cannot be kept too sweet, 'a branch for each of these) ; and these branches may be carried between the beams which support the deck, till they come to the side of the ship, and there be let down likewise between the beams into the places intended ; by which contrivance their operation will not in the least be obstructed, and the tubes be fecured from any accident.
The simplicity of this machine, it being fo little cumbersome, its operation without any labour to the seamen, the small expense to put it in execution, and maintain it, besides the forementioned considerations, are other arguments for its general use.
Continuation of the historical account of a
new method, &c.
Ince my first letter to you, giving an historical ac-