A Description of Dr. Hales's Ventilators fixed in Newgate; where being work'd by a Windmill they draw the foul Air out of the several Wards; which were made by Mr stibbs, Carpenter in Fore street, London Wall.

The ventilators fixed this month in Newgate by order of the lord mayor, sheriffs and aldermen of London, being the first of the kind, worked by a windmill, I thought it of more service to mankind, both in this and other countries, now to publish a particular account of them, than to defer it till the publication of the second volume of my book of ventilators; in the first volume of which there is a particular description of the method of making ventilators.

b b, the midriffs of these ventilators, are each nine feet long, and four and a half feet wide. Two pair of these ventilators are layed on each other, as in fig. 1. abcd. The midriffs of both ventilators are to be moved up and down by the flat iron rods e f, which have a joynt at f, where they are fixed to the midriffs, then passing through the upper part of the lower ventilator, and through the bottom of the upper ventilator, and also through an iron plate at g about three inches square; this plate to be covered by another broader iron plate, which is to be screwed fast to the bottom of the upper ventilator: this upper plate has a wide hole in its middle, to give room for the iron rod at g to move sideways to and fro, with the under plate, the hole of which exactly fits the iron rod, by which means no air can escape at g; and the like plates are at i, which is the top of the ventilator: at fg, are joynts, where the iron rods are fixed to the midriffs; by this means both midriffs are moved up and down at the same time. And the iron rods of both sides of the ventilators being fixed to one common lever at e e, all the four midriffs are thereby alternately worked up and down at the same time.

The circular ends of the ventilators, as well as all other parts, are fastened with wood screws dawbed with grease to prevent their rusting in the wood, so that any part can be taken off commodiously, to rectifie any failure in them.

v v v v x x x x are the valve-holes, which are 23 inches long, and six and a half inches wide. The valves are covered with buckram glued on them, for their greater strength; and if some linseed oyl is mixed with the glue, it will prevent its softening with moist air. The valves move on lifts of tanned sheepskin, and fall on lifts of woollen cloth nailed round the valve-holes, to break the force of their fall, and better to prevent the escape of the air.

A very large nose, (fig . 2) is fixed with iron hooks to the ventilators at l l, which nose is divided into three spaces. The middle or largest of these spaces, m m, receives all the foul air which is blown into it, from the eight middle valves x x x x, whence it passes thro' a trunk tt, sixteen inches wide, up through the leads of Newgate, into the open air. The top of this trunk is covered with weather boards to keep the rain out; the middle valves xxxx hang so as to open outwards.

The two other outer spaces or partitions of the nose pp, receive the foul air, which is drawn into them, from the several wards thro the trunks, pp, and passes off into the ventilators, through the eight outer valve - holes, v v v v, whose valves are hung so as to open inwards.

As the several branching trunks are to be opened and shut, as it shall be found proper to ventilate or not ventilate the several wards their order to spoiling the midriffs of the ventilators, for want of supply of air, when all the trunks may happen to be closed, it was therefore requisite to have two holes cut in the outer nostrils or partitions of the nose, at z z, each hole to be 18 inches long, and 10 inches broad or high, and 12 inches deep, and to have these holes covered with boxes, 20 inches long, and 14 inches wide, to be fastened with sliding fillets like drawers. The bottom of each of these boxes, to be a large moveable valve, opening upwards, and towards the ventilators. These may be called sniffling valves, because they are to be made of such a weight, viz. of half inch thick fir boards, as to open only when all the trunks to the several wards are shut; whereby the ventilators will always be supplyed with air, so as not to endanger the breaking the midriffs for want of it.

And in order the better to strengthen the head cross rail of the midriffs, that they may not be broken by the quick jerks of the crank of the windmill, when it turns fast, a strong iron plate is fixed to that rail, and for the same reason the iron axletree at the other binge end of the midriffs is fix'd with clams or claws to the ends of the long rail.

And in order to prevent the inconvenience of shrinking or swelling of the midriffs, it is found requisite, that the shoulders of the short cross rails should be one fourth of an inch short of the long rails: and their tennons not to be pinned, but fastened with a lift of iron lapping round the long rail; and fastened on both sides with wood screws, to the cross short rails. The grooves also of the pannels of the midriffs are deep enough to receive the swelling pannels.

The lever which moves the midriffs up and down is strong, and fourteen feet long, that the ventilators may the more easily be worked by men, if needful in long calm weather.

A weight equal to the weight of the iron rod, which reaches from the crank of the mill's axletree, down to one arm of the lever of the ventilators, is fixed on the opposite arm, there by to take off the resistance of the weight of that iron rod to the motion of the mill.

The ventilators are about 18 inches deep in the clear, thereby to allow for the thickness of the midriffs; and that they may not strike against the top and bottom of the ventilators, which would spoil them.

These ventilators are fixed in an upper room of Newgate, in order to be near the windmill on the leads, which works them. From each of the outer nostrils, there goes a trunk, which are twelve inches in the clear withinside; these trunks pass along on each side of the open area over the gate way, but at some distance from the sides of the area. And then descend thro' all the floors as far as a little below the cieling of the ground rooms; and are covered with plate iron within the reach of the prisoners.

From these descending trunks, lesser trunks, six inches square within, branch off near the cieling of every room. These branching trunks may be larger or smaller, according to the different sizes of the wards, and also in proportion to the greater or less numbers of prisoners that are usually there.

These branching trunks are to extend more or less into the several wards, in such manner, that when the foul air is drawn out of any ward, the fresh air may enter on the opposite side; and by that means drive all the foul air out before it. And in case there are several inletts for fresh air on opposite sides of the same ward, then the trunk reaches to the middle of the cieling of such ward.

And that many wards may be ventilated at the same time, there are sliding shutters with long handles, which slide up and down in staples; in order, not only to ventilate several wards at a time, by partly closing the side trunks; but also wholly to shut up the trunks of some wards, while others are ventilating. The handles of these sliders are locked fast, that it may not be in the power of the prisoners to shut or open them. In order to find out in what proportion to close with sliding shutters the trunks of the several wards that are to be ventilated at the fame time, it will be needful at first to tye a lighted candle at the end of a pole, and hold it at the mouths of the trunks, thereby to make some estimate of the quantity of foul air that is drawn into the several trunks.

And when the upper floors are ventilating, the air is hindred from being drawn out of the lower floors, either by shutting all their trunks, or by a sliding iron, which shuts the descending trunk, near the floor of the lowest of the rooms that are ventilated. But when the wards of the lower floors are to be ventilated, then all the side branching trunks of the upper floors are to be shut, that the whole effect of ventilation may be in the wards of the lower floors.

By this means, all the wards may be ventilated in their turns, in such proportion as shall by experience be found most convenient.

All these sliding shutters have large figures, viz . 1 , 2 , 3 , &c. painted on them; that by these numbers they may more easily be described, and referred to, in the several directions for ventilating the several wards.

In the case of a prison that is built with an open area or court in the middle; in this case, the side of the prison which is opposite to the side, where the ventilators are, may commodiously be ventilated in its turn, by having a round brick air gutter under ground, through which the foul air of those wards may easily be drawn.

In lesser prisons the ventilators need be but one half of these in Newgate, which may easily be worked by men; as is found by experience in several prisons and hospitals.

The like ventilators, to be worked either by a wind or water mill, will be of great use to preserve great quantities of corn in granaries. This, M. du Hamel de Monceau, Member of the Royal Academy of sciences, has, on my proposal of it to him, actually put in practice, by fixing a windmill on a publick granary which works large ventilators, that convey plenty of air up through the corn. And where it can be had, a water mill would be much the best, because it could work constantly during the whole day; by which means a vast quantity of corn of any depth might be preserved in one granary, and that with no great expence in building it.

The air might be conveyed thro' small trunks about 4 inches square, layed on the floor of the granary at the distance of about four feet from each other. The four joynts or seams of the trunks to be about one tenth of an inch wide, for the air to pass thro' their whole length. These trunks to be supplied with air from the ventilators thro' a larger trunk layed across them, either at one end, or in the middle of the granaries, according to the largeness or smallness of the granary. This has been found by experience a cheap and good method.

Mines might be made very wholsome by means of large ventilators, to convey plenty of air through trunks to the farthest parts of them. They might be worked either by a stream in the mine or on the surface of the earth; or, as Mr Erasmus King very rightly proposes, by the fire engine which draws the water out of some mines, or, where neither of these conveniences can be had, then by a windmill, which as it would be becalmed about one fourth of the year, during those times by a horse.

The small ventilators, fig. 6, in the ventilator book, would be of great use to make the air of an air-shaft wholsome, while digging; and to blow away the fumes of gunpowder immediately when a rock is blown up with it. And this may be done by letting down a trunk about four inches wide into the shaft, with a trunk of canvas at its lower end, which will readily comply to go lower and lower, as the shaft is dug deeper.

And whereas in some lead &c. mines, the large mine is pretty healthy, by having a progressive motion in the air; but yet the side branching mines unhealthy, for want of such a current or motion in the air in this case, the small ventilator, fig. 6, might be of service, if placed not far from the mouth of the branching mine; there to blow into it the less impure air of the main mine.

It is well known, by long and too frequent experience, that the destructive goal distemper is occasioned by the bad air in prisons, which is filled with the great quantity of vapours that arise from the breath and perspiration of the prisoners; which being, as Dr Keil found it here in England, at the rate of 39 ounces in 24 hours, from one person, this in 100 prisoners will amount to 243 pounds. Now such close confined air, by long stagnating is very apt to putrefy; and putrefaction being the most subtile and powerful dissolvent in nature , it dissolves the blood and humors of human bodies, and thereby produces that very infectious, pestilential disease, which is called the goal distemper. And such close-confined, damp, putrid air will not only dissolve human bodies, which are framed of materials strongly tending to putrefaction, but also even heart of oak, as is well known by daily experience every where.

The undoubted benefit of thus ventilating prisons is very evident by the following experiment, viz. At my desire, Dr Langrish, a physician at Winchester, burnt a candle of six to the pound in the dungeon of that prison, in the morning, before doors or shutters had been opened; where it wasted in half an hour 66 1/2 grains, candle had wasted 88 grains burning as long in a good air. And after the dungeon had been well ventilated with ventilators for half an hour, the prisoners remaining there all the while, the same candle wasted in another half hour 87 1/2 grains, that is very nearly as much as in a good air at first; which sufficiently shows the great usefulness of ventilators, in prisons, ships and hospitals; for as a candle burns more or less vigorously in proportion to the degrees of purity or impurity of the air, so is our vital lamp proportionaby either enlivened, or incommoded, or totally quenched, according to the different degrees of purity or impurity of the air which we breathe.

The doctor observed that at the first going down into the dungeon the air affected the mouth and throat with a remarkable saltness, but not at all, at their going down after it had been well ventilated.

A Description of the Windmill, which is fixed on Newgate to work the Ventilators; this Mill was made by Mr Cowper in Penny Fields Poplar.

As this mill is designed and contrived to move with a small degree of wind, and withal to obtain a sufficient power in a small compass, I thought it requisite to give a draught and description of it.

c, fig 2. is one of the cross trees which support the mill post d, and the spurs or braces e e; which cross trees rest on the blocks a, where they are fixed to the floor they stand on, by strong iron bolts, screwed fast under the floor. b, the crown tree, to steady the iron rod that passes there through brass collars, which are contrived to as to screw closer together as they wear away. d is the main oaken post, which is bored hollow for the iron rod b to pass thro from the crank of the iron axletree i. f is the girdle on which the turning frame g moves; on this girdle lies a broad circular iron plate, on which the brass friction wheels have their bearing, and these wheels are so placed at different distances as to turn on different parts of the plate, and thereby save its wearing all in one circle. These wheels are three quarters of an inch thick, and five and half inches in diameter, their iron axletrees are an inch thick, and move in brass collars. g, n, is the turning frame which carries the axletree i i, and the sails l k, which are turned so as always to face the wind, by the vane b. g r, the double pricked lines, are iron braces, which are fastened at each end with iron screw bolts to keep the frame from wracking. z is the crank, which is six and half inches long, and therefore gives a stroke of thirteen inches: but the lower end of the iron rod x is fixed to the lever of the ventilator, fig. 1, at such a distance from the centre of its motion, as to raise and fall the midriff's 15 inches; there are brass collars at the joyning of the iron rod to the crank, and also at the bearings of the axletree, which collars are screwed nearer and nearer as they wear away. The iron axletree extends forward about two feet and half beyond the face of the sails, from the extremity of which, s, eight iron braces, l l go to each arm, to which they are fastened by iron screw bolts, which bind them and the iron circle of pricked lines m m fast together; the diameter of this iron circle is six feet. The sweeps or arms of the mill k k are seven feet 3 inches long. They are morticed into the knave or drum y y. And as an angle of 55 degrees is found, both by mathematical calculations and by experience with a small windmill placed before the nose of my ventilators, to be the degree of weathering, as millwrights call it, or the angle or oblique position of the sail to the wind, for obtaining the greater force, so an angle near that, viz. of 60 degrees, has been found by experience of the right honorable the earl of Northumberland, as he informed me, to do very well, in such small mills. But in common mill with very long arms, the obliquity of the sails ought to be less; else their great velocity will, in strong winds, cause a counteracting force at the back of the sails. In order to avoid this inconvenience Mr Cowper very rightly proposed, not to fill up the whole space with sails, but to leave a void space of about six inches breadth between the sails, as is represented in the sails m m that the direct current of the wind, as it passed through there, might carry along with it, and give a turn to the course of the wind, which else, being drove obliquely from the face of the preceding fail, would thereby be drove to act on the back of the following sail, and thereby abate the force and retard the motion of the mill.

If common windmills were constructed in this manner, it seems probable that their arms might be much shorter, which would be more commodious in several respects.

n is the brake pole; and the single pricked line at the end of it, is the sword which is to clasp round the nave to stop the mill, by pulling the rope w which is expressed by the scroll line. o is the bottom shere tree of the turning frame. p expresses the manner of screwing the brass collars of the axle tree nearer and nearer as they wear away.

An Account of the Nature and Uses of Ventilators, with the Manner of making and placing these useful Machines.

Illustrated with a Copper-plate, containing, besides the Ventilators, a perspective View of the Wind-mill, lately erected on Newgate, for working the Ventilators in that Prison.

The air itself has so great a share in the action of respiration, and is likewise so necessary to the health and vigour of the body, that no remarkable alteration can be made in it without our being sensibly affected by it. Confequently, when the air we breathe is loaded with vapours, which either render it too warm, or destroy its elasticity, or both, it becomes unfit for respiration, and interferes with the action of breathing. Also, unless the chyle, which is mixed with the blood, be brought to the lungs in proper quantities, and endowed with proper qualities; unless the discharges through the sides of the vesicles of the lungs be regularly and duly performed; unless a proper quantity of air-particles be absorbed, to supply the active principles, so necessary to the warmth of the blood, and the cohesion of its parts; it must, by degrees, grow less and less fit for the purposes of life: so that, by degrees, the blood will be so impaired and broken, that, when it most wants the assistance of the lungs, it will be brought thither, when it is only fit to choak up and clog the vesicles and capillary arteries, so as to prevent the receiving the service it could receive in passing through the lungs. Hence it is no wonder, that, when we breathe an air thus loaded with vapours, it hould be apt to cause what is called the gaol-distemper; which inconvenience might, in a great measure, be prevented, if close prisons were ventilated with srefh air; for want of which many unhappy persons are not only deprived of liberty, in gaols, but also too often even of life.

And, as the air in ships is often much more rancid than in prisons, on account of the great number of persons on board, it must also tend to make them very sickly, and confequently less able to contend with the inclemency of air, that a change from a cold to a very hot climate causes. Therefore, ventilators will be of the greatest use on board ships of war, by producing a conftant gentle supply of fresh air, and be the means of preserving the lives of thousands.

They will be also of great use in drying malt, hops, &c, and many other occasions of life; but for these we must refer to the inventor, the learned Dr. Hales's book, intitled, A Description of Ventilators.

It is evident, that large bellows are worked with labour, because it is necessary to have the air compressed in them, in order to make it move with velocity and force through small orifices; but, if the valves and passages were very large, they might be worked to and fro with the greatest ease, as is evident in the case of common bellows, which will move up and down with surprising ease, if their valve be held open with a finger. And the case would be the same, if the bellows were very large, provided the valves were made to open and shut easily, and of a proportional bigness. For, in this case, we only want to move a quantity of light uncompressed air from the outside to the inside of the place where it is desired, or from within outward. And, since a tun, or forty cubic feet of air in bulk, weighs only 300 grains, which is not quite three quarters of an ounce, suppose a pair of bellows were so large as to contain a tun, yet that tun of air would give litle resistance to the contracting bellows, provided the valves and windpipes, leading to and from them, were proportionally large: and, for the same reason, the dilatation of the bellows would be equally easy. Thus we breathe to and fro, through a large wind-pipe, about fixteen tuns of air in twenty-four hours, with little or no labour. And in this consists the excellency of these machines called ventilators, as they convey air by a method the most simple and analegous to that which nature makes use of to convey fresh air into the lungs of men, and other animals, viz. by the easy rising and falling of the midriff.

These things being premised, the following description of ventilators may be easily understood.

A, B,C, D (see the copper-plate, fig. 2.) represents a box about ten feet long, five wide, and two deep, in the middle of which is placed a broad partition, or midriff, made to move up and down from A to C, on hinges, at the end FE, by means of an iron rod, ZR, fixed to the midriff at Z. Another box of the same size of the former, having a like midriff bar, &c. is placed near the former (see fig. 4.) with its rod R Z ; both these rods are fixed to a lever F G, moveable on the center O ; so that, by the alternate rising and depressing of the lever F G, the midriffs are also raised and depressed alternately, by which means the double bellows are at the same time both drawing in, and pouring out air. That the midriffs may be rendered lighter, they may be made of four bars lengthways, and as many placed across them, each about three inches broad and an inch thick, the vacant spaces being filled up with thin pannels of fir board.

In order to make the midriffs move with greater ease, and without touching the sides of the boxes, there is an iron regulator N L (fig. 2.) fixed upright to the middle of the end of the box AC. As very little air will escape, if the edges of the midriff be within one twentieth part of an inch from the sides of the box, there is no necessity for leathern sides, as in common bellows, which would render them more expensive, and at the same time make them move more heavily. The end a AC of the box must be somewhat circular, that it may be the better adapted to the rising and falling of the midriff, and at the other end of the midriff a slip of leather may be nailed over the hinges.

To the ventilators above described eight valves are adapted for the air to pass through; these valves are placed at the hinge end (BQ, fig. 4.) of the boxes, which, in the figure, are numbers, 1, 2, 3, 4, 5, 6, 7, 8. The valve I, opens inward, to admit the air to enter, when the midriff ts depressed at the other end, by means of the lever FG. And, at the same time, the valve 3, in the lower ventilator, is shut by the compressed air, which passes out at the valve 4. But, when that midriff is raised, the valve 1 shuts, and the air passes out at the valve z. The same is to be observed of the valves 5, 6, 7, 8, of the other box; so that when, by the motion of the lever F G, the midriffs are alternately rising and falling, then two of the ventilators are constantly drawing in air, and two of them at the same time are blowing it out at their proper valves; the air entering at the valves 1, 3, 6, 8, and passing out at the valves 2, 4, 5, 7.

To the ventilators, before the valves, is fixed a box QQ MM (fig. 3.) as a common receptacle for all the air that comes out of these valves, which air is conveyed away through the trunk P, passing through the wall of a building, &c.

From the foregoing explanation, the nature of ventilators may be easily understood, and therefore we shall be briefer in the following description of those lately erected in Newgate, for exhausting that prison of its foul air.

In this pridon there are seven ventilators, each nine feet long, and four and a half feet wide; two pair of which are laid on each other. These ventilators are worked by means of a windmill (fig. 6.) an explanation of which we shall give hereafter.

The valves of the ventilators open into a large wooden box A B (fig. 5.) which is fastened to the ventilators by the hooks A, A. This box is divided into three spaces; the middle, or largest CC, receives all the foul air discharged by the ventilators, whence it passes through a trunk D D, fixteen inches wide, through the leads of Newgate, into the open air. The outer spaces, B, B, B, B, receive the foul air thro' the trunks F, F, from the several wards, from whence it is conveyed into the ventilators through those valves which open inward, and then discharged, by the other valves of the ventilators, into the middle partition of the box, and from thence conveyed, by the pipe D D, into the open air, as we before observed.

These ventilators are fixed in an upper room of Newgate, in order to be near the leads, where the windmill which works them is erected; and, from each of the outer nostrils F F, there are trunks, with sliding shutters, passing into the several wards, so that, by opening these trunks, any of the wards may be ventilated, either singly or several at a time.

That the midriffs may not be spoiled for want of air, when all the trunks are shut, there are two holes cut in the outer nostrils at E E, which are covered with boxes twenty inches long, and fourteen wide. In the bottom of each of these boxes is a large moveable valve, of such a weight, as not to open, but when all the other passages for the air are stopped; by means of these valves, the ventilators are supplied with air, when all the trunks going into the several wards are closed, and the midriffs not in danger of breaking for want of it.

A Description of the Wind-mill lately erected by Mr. Cooper, of Penny-fields, Poplar, on Leads of Newgate, for working the Ventilators.

This mill is designed to move with a small degree of wind, that the ventilators may be the oftener worked. The mill-post is fixed on four cross-trees and supported by the braces u, w, x, y (fig. 6.) This post is hollow, that the iron rod a may pass through the lower end of it, being fixed to the lever of the ventilators. The upper end of this rod goes to the iron axle-tree, which has a crank six inches long, and, therefore, gives a stroke of thirteen inches; and the other end, being fixed to the lever at a proper distance from the center of its motion, raises the midriffs fifteen inches. The iron axle-tree extends about two feet beyond the face of the sails, from the extremity of which, p, eight iron braces go to the vanes m, n, o, p, q, r, s, &c. as expressed in the figure. The frame turns on the post on friction wheels, so that the sails always face the wind, by means of the vane i, on which is painted the city arms. l, is the break-pole, which, by pulling the rope k, stops the mill. b d, c e, are iron braces, fastened at each end with iron bolts, to keep the frame from wracking.

Hales was a keen letter writer in furtherance of his aims, and via his letters, some of which were published we gain additional information.

He lobbied hard to get the Newgate ventilators and windmill built, invoking patriotism (we must do it before the French - who he had already told about ventilating granaries), hyperbole (it will benefit the whole world), national interest (if we show the French by example, then they may treat our POWs in their jails better), his own self interest (I want to be able to write about it in my next book!), as well as the closing plea of the humanity of stopping unnecesary deaths by going ahead with the plan. 11 July 1751, to Alderman Janssen

Teddington, 11 July, 1751.
To Mr. Alderman, Yanssen,
SIR,

Not having Time, when I was with you 'tother Day at Richmond, to talk to you fully of the Affair I came about, I shall do it fully in this Letter, viz.

Last Year, when many died of the pestilential infectious Jail Distemper, which they got in the Old Bailey Court, there was, on that Occasion, a Probability, that large Ventilators would be fixed in Newgate, to be worked by a Windmill, as you saw was done on board a Man of War at Deptford, which would effectually preserve all the Wards in Newgate in a sweet healthy state.

> I then wrote an Account of this Design to Mons. Du Hamel at Paris, who is Inspector of all the Ports in France, and at the same Time, proposed to him to make Use of the same Method to preserve great Quantities of Corn in Granaries, by the same Means. — He was so pleased with the Proposal, that he immediately fixed a Windmill, on a great Public Granary at Paris, which by working large Ventilators, blows Plenty of fresh Air upwards through the Corn which so effectually preserves the Corn, that it is like to become a National Practice; of which he has sent me a particular Account, with Drafts describing how it is done. I have written him Word, that where it can be had, a Water-Mill will do much better.

I have not yet given the French a particular Account, of what I have done on board the Sheerness Man of War, towards preserving the Timbers of ships layed up in ordinary, because I was desirous we should have the Credit of first doing the Thing. But as the Commissioners of the Navy, to avoid a trifling Expence, (which would most assuredly save Millions to the Nation) have put a Stop to my Proceedings, when I was got only to the Threshold of the Experimental Research, and had as yet tried only the fourteenth Part of the Air that would convey it among the Timbers of a ship: For in new Researches we are under a Necessity of feeling out our Way step by step. — Since I am thus stopt short in this important Research, I intend, before Christmas, to publish the second Volume of my Book upon Ventilators, in which, among other things, both in Justice to the Public, and in Vindication of the Reasonableness of my Proposal, I will give a full Account of it, and of the high Probability, I will say Certainty of success, in preserving the Timber of ships many Years the longer from decaying.

This will probably put the Frenth upon doing the thing, and then we shall have the Disgrace of copying after them, which we must now do, if we should ever attempt it, to preserve Corn in Granaries, as Mons. Du Hamel has done.

I am sensible that the Deliberations, whether Newgate should be pulled down and new built, have with good Reason delayed the fixing of Ventilators there. — But if it is, or shall soon be resolved, that Newgate shall not be pulled down; then, I could wish, if it is at all to be done, that it might be done before the next Winter; that I may be enabled to give an Account of its being done, in my second Volume; else we may stand a fair Chance to learn that of the French too.

I am the more desirous to have it done in Newgate, not only for the sake of the Prisoners there, but also as a laudable Pattern, not only for the rest of the Nation, but for the Benefit of the World.

Of what Importance will this be to the Nation, when we engage in War, to have our brave undaunted Sailors and Soldiers, when Prisoners of War, preserved from being poisoned and rotting in Jails? For it is highly probable, that three in four of those who die in War, loose their Lives by the stench of Jails, and Hospitals.

I have several years since wrote to Mons. Du Hamel, to propose the Ventilating the Prisons of Prisoners of War, and if the Example was set at Newgate, the good Effect of it would probably induce the several warring Nations, on both sides, to do so great an Act of Humanity.

Thus you see, Sir, that what I am so desirous of having done in Newgate, is an Affair of the greatest Importance, not only to this Nation, but to the whole World.

I am therefore persuaded that the oppulent and renowned City of London will not long hesitate about it. When you and several other Aldermen, with Dr. Pringle and myself, went in October last into Newgate, we were but too sensible of the stench of several of the principal Wards, a stench so very offensive, that it would be a great Act of Humanity to deliver, not only unhappy Debtors, but even the vilest of Criminals from it; even though it occasioned netither the Sickness nor the Death of any. But when, withal, we are assured, it causes the Sickness and Death of many, can anyone hesitate, whether an effectual Means shall be made use of to cure so destructive a Pest. I am,

SIR, your obliged humble servant, Stephen Hales.

In 1762 the young man W Pickett who had been my elder apprentice got embarrassed and thrown into the King's Bench for debt. As soon as I was acquainted with his situation I visited him. There appeared nothing of what I conceived to be a prison except the door of admission and high walls. There was a coffee room and a tap room both filled with persons drinking, though it was sunday, and I had never before seen such a number of profligates and prostitutes, unabashed, without fears, without blushes. I thought, to be sure, all the wicked people in London had got together there. ... My ideas of a prison not being at all answered in the King's Bench, I procured admission into Newgate as far as the press yard and the room extending over the street, which had a windmill ventilator. In this room all the prisoners were in irons and amongst them one a very stout man seemingly at the point of death.

Hales work on ventilation was very successful, and became a standard scientific reference in the following decades. The existing diagram appeared illustrating pneumatics/ventilation in 1786/8, with the plates various labelled "I Taylor" or "Lowrey sc., Published according to Act of Parliament by Alex Hogg at the Kings Arms, No. 16 Paternoster Row".

In 1819, the huge undertaking of the Abraham Rees "Cyclopedia or Universal Dictionary of Arts, sciences, and Literature" was published by Longman, Hurst, Reec, Orm & Brown, Paternoster Row, with the windmill diagram appearsing in modified form (it has been mirrored, and lost the emblem of the City of London on the wind vane), as Plate XVII. This diagram is referenced from the article on the ventilator, extracts of which say:

The air of gaols has been often known to be infectious; and we had a fatal proof of this, by the accident that happened some years ago at the sessions at the Old Bailey. To guard against the like for the future, as well as to preserve the health of the prisoners, a worthy magistrate, in 1752, had ventilators placed in Newgate, which were wrought by a windmill; and in the beginning of the year 1753, Dr. Hales gave an account of the good success attending the use of these machines, by a remarkable decrease in the usual mortality and sickness of that place.

Although the old prison at Newgate is now taken down, and a much more commodious one erected near the same spot, it may not be improper to give a brief account of the manner in which the ventilators of Dr. Hales were constructed, and how they were moved by the windmill annexed to them. The midriffs h, h, (Fig. 4.) of these two ventilators, two pair of which were laid upon one another, were each nine feet long, and four and a half wide, and moved up and down by the flat iron rods e,f, passing through the lower and upper ventilators, and through an iron plate at z, about three inches square; over which is another broader iron plate, with a wide hole in its middle, to give room for the iron rod at g to move sideways to and fro, with the under plate, the hole of which exactly fits the iron rod, so that no air can escape at g; and there are the like plates at i, the top of the ventilator; and at f, g, are joints, where the iron rods are fixed to the midriffs, by which means both are moved up and down at the same time; and the iron rods of both sides of the ventilators being fixed to one common lever at e e, all the four midriffs are thereby alternately worked up and down at the same time. The valve-holes v, v, x, x, &c. are twenty-three inches long, and six and a half wide, covered with buckram glued on them, and move on lifts of tanned sheep-skin, and fall on lifts of woollen cloth nailed round the valve-holes. A very large nose (fig- 5.) is fixed with iron hooks k, k, to the ventilators l, l; and this nose is divided into three spaces, the middle and largest of which, m m, receives all the foul air blown into it from the eight middle valves x, x, x, x, (fig- 4.), whence it passed through a trunk t t, fixteen inches wide, through the leads of the prison, into the open air; the top of this trunk being covered with weatherboards to keep the rain out, and the middle valves hanging so as to open outwards. The two other outer spaces of the nose p p, receive the foul air, drawn into them, from the several wards, through the trunks p, p, and passing off into the ventilators, through the eight outer valve-holes v v, v, v, whose valves open inwards. In these outer partitions of the nose there are two holes z, z, (fig. 5.) covered with boxes, in the bottom of each of which there is a large moveable valve, opening upwards, and towards the ventilators: these are made of such a weight, as to open only when all the trunks to the several wards are shut: by which the ventilators will always be supplied with air, so as not to endanger the breaking of the midriffs for want of it. These ventilators, about eighteen inches deep in the clear, were fixed in an upper room of Newgate, in order to be near the windmill on the leads, which worked them. From each of the outer nostrils there went a trunk, twelve inches in the clear withinside; and from these trunks, which descended through all the floors as far as a little below the ceiling of the ground rooms, lesser trunks, six inches square within, branched off, near the ceiling of every room; and extended more or less into the several wards, so that when the foul air was drawn out of any ward, the fresh air might enter on the opposite side, and drive out all the foul air before it. By other contrivances with sliding shutters and handles, the several wards might be ventilated at such a time, or in such a degree, as was found necessary. In the case of a prison that is built with an open area in the middle, Dr. Hales observes, that the side of the prison which is opposite to the side where the ventilators are, may be commodiously ventilated in its turn, by having a round brick air-gutter under ground; through which the foul air of those wards might eafily be drawn.

The windmill for working the ventilators was contrived to move with a small degree of wind, and to obtain a sufficient power in a small compass. In fig. 6, c is one of the cross-trees which support the mill-post d, and the braces e, e; the cross-trees rest on the blocks a, a, and are fixed to the floor by strong iron bolts. The mill-post J, being hollow, admits the iron rod b to pass through from the crank of the iron axle-tree i; the turning-frame g n moves on the girdle f, on which lies a broad circular iron plate, where is the bearing of the brass friction-wheels, whose iron axle-trees move in brass collars: the turning-frame g n carries the axle-tree i i, and the sails l, k, which are turned, so as always to face the wind, by the vane h; the frame is kept from wracking by iron braces q, r, represented by the double pricked lines. The crank z is six inches and a half long, and therefore gives a sroke of thirteen inches; but the lower end of the rod r is fixed to the lever of the ventilator (fig. 4) at such a distance from the centre of its motion, as to raise and fall the midriffs fifteen inches. The iron axle-tree extends forward, about two feet and a half beyond the face of the sails; from the extremity of which, s, eight iron braces, l, l, go to each arm, to which they are fastened by iron screwbolts, which bind them and the iron circle of pricked lines m m (fig. 7.) fast together: the diameter of this circle is six feet, and the sweeps or arms of the mill k k are seven feet three inches long, and they are mortifed into the drum y y. A void space of about six inches breadth is left between the sails, as represented in the figure, that the direst current of the wind, as it passed through, might give a turn to the course of the wind; which otherwise, being driven obliquely from the face of the preceding sail, would be forced to act on the back of the following sail, and thereby abate the force, and retard the motion of the mill. The brake-pole (fig. 6.) is n; and the single pricked line t at the end of it is the sword which is to clasp round the nave to stop the mill, by pulling the rope w: o o is the bottom shear-tree of the turning-frame; and p expresses the manner of screwing the brass collars of the axle-tree nearer and nearer, as they wear away. For a farther account of this machine, see Hales's Treatise of Ventilators, part ii. 1758, p. 32, &c.

Dr. Hales farther suggests, that ventilators might be of life in making salt, in order to which 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 or canvas, about a foot above the surface of the brine, in order 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 a rainy or dry state of the air. Ventilators, he apprehends, might also serve for drying linen hung in low, long, narrow galleries, especially in damp, rainy weather, and also in drying woollen cloths, after they are fulled or dyed, and in this case they might be worked by the fulling water-mill.