expel the air and obstructing matter by violent coughing.

BIRDS, as above hinted, exhibit a curious va riety in the process of breathing. The muscles of their wings being fo very great, require a very extenfive infertion, and this is one ufe of the great breaft bone. Another ufe of it is, to form a firm partition to hinder the action of thefe mufcles from compreffing the thorax in the act of flying: there fore the form of their cheft does not admit of alternate enlargement and contraction to the degree. as in land animals. The mufcles of their abdomen are alfo very fmall; and they are not fufficient for producing the comprellion on the bowels which is neceffary for carrying on the procefs of concoction and digeftion. Instead of aiding the lungs, they receive help from them..

The lungs of an oftrich confift of a fleshy part A, A (fig. 66. Plate 282.), compofed of vehicles like thofe of land animals, and, like theirs, ferving to expofe the blood to the action of the air.. Befides thefe, they have on each fide four large bags B, C, D, E, each of which has an orifice G communicating with the trachea; but the fecond, C, has alfo an orifice H, by which it communicates with another bag F fituated below the reft in the abdomen. When the lungs are compreffed by the action of the diaphragm, the air in C is partly expelled by the trachea through the orifice G, and partly driven through the orifice H into the bag F, which is then allowed to receive it; becaufe the fame action which compreffes the lungs enlarges the abdomen, When the thorax is enlarged, the bag C is partly fupplied with fresh air through the trachea, and partly from the bag F. As the lungs of other animals refemble common bellows, the lungs of birds resemble the fmith's bellows with a partition; and anatomifts have difcovered paflages from this part of the lungs into their hollow bones and quills. This alternate action muft afhift the mufcles of the abdomen in promoting the motion of the food along the alimentary canal, &c. In birds, their belly dilates when the cheft collapfes, and vice verfa, contrary to what we fee in the land animals. This double paffage may alfo produce a circulation of air in the lungs, to compenfate for the smaller furface of action on the blood: for the number of small veficles, of equal capacity with these large bags, gives a much more extenfive furface.

When we try to raise mercury in a pipe by the action of the cheft alone, we cannot raife it above 2 or 3 inches; and the attempt is both painful and hazardous. But we can by expiration fupport mercury about 5 or 6 inches high, though this alfo is very painful, and apt to produce ex'travafation of blood. This feems to be done entirely by the abdominal muscles.

The a& of SUCKING is totally different from breathing, and refembles the action of a common pump. Suppofe a pipe held in the mouth, and its lower and immerfed in water. We fill the mouth with the tongue, bringing it forward, and applying it clofely to the teeth and to the palate; we then draw it back, or bend it downwards (bebind) from the palate, thus leaving a void. The preffure of the air on the cheeks immediately de

preffes them, and applies them clofe to the gums and teeth; and its preffure on the water in the veffel caufes it to rife through the pipe into the empty part of the mouth, which it quickly fills. We then push forward the tip of the tongue, below the water, to the teeth, and apply it to them all round, the water being above the tongue, which is kept much depreffed. We then apply the tongue to the palate, beginning at the tip, and gradually going backward in this application. The water is thus gradually forced backward by an operation fimilar to that of the gullet in fwallowing. This is done by contracting the gullet above, and relaxing it below, whereby the mouth is again completely occupied by the tongue, and we are ready for repeating the operation. Thus the mouth and tongue refemble the barrel and pifton of a pump; and the application of the tip of the tongue to the teeth performs the office of the valve at the bottom of the barrel, preventing the return of the water into the pipe. Although ufual, it is not abfolutely neceffary, to withdraw the tip of the tongue, making a void before it. Sucking may be performed by merely feparating the tongue gradually from the palate, beginning at the root. If we withdraw the tip of the tongue a very minute quantity, the water gets in and flows back above the tongue.

The action of the tongue in this operation is very powerful; fome perfons can raife mercury 25 inches: but this strong exertion is very fatigu ing, and the foft parts are prodigiously fwelled by it. It caufes the blood to ooze plentifully through the pores of the tongue, fauces, and palate, as if a cupping-glafs and fyringe were applied to them; and, when the infide of the mouth is excoriated or tender, as is frequent with infants, even a very moderate exertion of this kind is accompanied with extravafation of blood. When children fuck the nurfes breaft, the milk follows their exertion by the preffure of the air on the breast; and a weak child, or one that withholds its exertion on account of pain from the above mentioned, caufe, may be affifted by a gentle preffure of the hand on the breaft: the infant pupil of nature, without any knowledge of pneumatics, frequently helps itself by preffing its face to the yielding breaft. In the whole of this operation the breathing is performed through the noftrils; and it is a prodigious diftrefs to an infant when this paffage is obftructed by mucus. This obftruction may be almost certainly removed, by rubbing the child's nofe with water or any liquid.

The act of drinking is not very different from that of fucking: we have indeed little occafion here to fuck, but we must do it a little. Dogs and fome other animals cannot drink, but only lap the water into their mouths with their tongue, and then fwallow it. The gallinaceous birds drink very imperfectly; they merely dip their head into the water up to their eyes, till their mouth is filled with water, and then holding up the head, it gets into the gullet by its weight, and is fwallowed. The elephant drinks in a very compli cated manner; he dips his trunk into the water, and fills it by making a void in his mouth, in the contrary way to mau. After having depressed

his tongue, he begins the application of it to the palate at the root, and by extending the application forward, he expels the air by the mouth which came into it from the trunk. The procefs here is like that of the condensing fyringe without a pifton valve, defcribed above in Sect. I. in which the external air (correfponding here to the air in the trunk) enters by the hole F in the fide, and is expelled through the hole in the end of the barrel; by this operation the trunk is filled with water: then he lifts his trunk out of the water, and bringing it to his mouth, pours the contents into it, and swallows it. It is a double operation, and cannot be carried on any way but by alternately fucking and swallowing; whereas man can do both at the fame time. Many infects, too, which drink with a trunk, drink without in terruption.

There is an operation fimilar to that of the elephant, which young chemifts and jewellers find a great difficulty in acquiring, viz. keeping up a continued blaft with a blow-pipe. We would defire our chemical reader to attend minutely to the gradual action of his tongue in fucking, and he will find it fuch as we have defcribed. Let him attend particularly to the way in which the tip of the tongue performs the office of a valve. preventing the return of the water into the pipe: the fame pofition of the tongue will hinder air from coming into the mouth. Next let him obferve, that in swallowing what water he has now got lodged above his tongue, he continues the tip of the tongue applied to the teeth; now let him fhut his mouth, keeping his lips firm together, the tip of the tongue at the teeth, and the whole tongue forcibly kept at a diftance from the palate; bring up the tongue to the palate, and allow the tip to feparate a little from the teeth; this will expel the air into the space between the fauces and cheeks, and will blow up the cheeks a little; then acting with the tip of the tongue as a valve, hinder this air from getting back, and depreffing the tongue again, more air (from the noftrils) will get into the mouth, which may be expelled into the space without the teeth as before, and the cheeks will be more inflated: confinue this operation, and the lips will no longer be able to retain it, and it will ooze through as long as the operation is continued. When this has become familiar and eafy, take the blow-pipe, and there will be no difficulty in maintaining a blaft as uniform as a fmith's bellows, breathing all the while through the noftrils. The only difficul. ty is the holding the pipe: this fatigues the lips; but it may be removed by giving the pipe a convenient fhape, a pretty flat oval, and wrapping it round with leather or thread.

Another phenomenon depending on the principles already established, is the land and fea breeze in the warm countries. As air expands exceedingly by heat, heated air, being lighter than an equal bulk of cold air, muft rife in it. Suppofe an inland receiving the first rays of the fun in a calm morning; the ground will foon be warmed, and will warm the contiguous air. If the inland be mountainous, the inclined fides of the hills will receive the light more directly; the midland air will therefore be moft warmed: the heated air

will rife, and that in the middle will rise fastest; and thus a current of air upwards will begin, which must be fupplied by air coming in from all fides, to be heated and to rife in its turn; and thus the morning fea-breeze is produced, and continues all day. This current will frequently be reverfed during the right, by the air cooling and gliding down the fides of the hills, and then we fhall have the land-breeze.

From the fame cause there is a circulation of air in mines which have the mouths of their shafts of unequal heights. The temperature under ground is pretty conftant through the year, while that of the atmosphere is extremely variable. Suppofe a mine having a long horizontal drift, communicating between two pits or fhafts, and that one of thefe terminates in a valley, while the other opens on the brow of a hill perhaps 100 feet higher. Suppofe it fummer, and the air heated to 65°, while the temperature of the earth is but 45; this laft will be alfo the temperature of the air in the fhafts and the drift. Now, fince air expands nearly 24 parts in 10000 by one degree of heat, we fhall have an odds of preffure at the bottom of the two fhafts equal to nearly the 20th part of the weight of a column of air 100 feet high: (100 feet being fuppofed the difference of the heights of the fhafts.) This will be about fix ounces on every fquare foot of the fection of the fhaft. If this preffure could be continued, it would produce a prodigious current of air down the long shaft, along the drift, and up the fhort fhaft. This preffure would be continued, if the warm air which enters the long fhaft were cooled and condensed as faft as it comes in; but this is not the cafe. It is however cooled and condenfed, and a current is produced fufficient to make an abundant circulation of air along the whole paffage; and care is taken to difpofe the fhafts and conduct the paffages in fuch a manner that no part of the mine is out of the circle. When any new lateral drift is made, the renewal of air at its extremity becomes more imperfect as it advances; and when it is carried a certain length, the air ftagnates and becomes fuffocating, till either a communication can be made with the reft of the mine, or a fhaft be made at the end of this drift.

As this current depends on the difference of temperature between the air below and that above, it must ceafe when this difference ceafes. Accord ingly, in the fpring and autumn, the miners complain much of ftagnation; but in fummer they never want a current from the deep pits to the fhallow, nor in winter a current from the fhallow pits to the deep ones. It often happens alfo, that the chemical changes which are going on in different parts of the earth make differences of temperature fufficient to produce a fenfible cur. rent.

The fame caufes muft produce a current down our chimneys in fummer. The chimney is colder than the fummer air, and muft therefore condenfe it, and it will come down and run out at the doors and windows. This leads us to confider a very important effect of the expansion and confequent afcent of air by heat, namely the drawing of chimneys. The air which has contributed to the burning of fuel must be intenfely heated, and will Ea

rife

rife in the atmosphere. This will also be the cafe with much of the furrounding air which has come very near the fire, although not in contact with it. If this heated air be made to rife in a pipe, it will be kept together, and therefore will not foon cool and collapfe: thus we fhall obtain a long column of light air, which will rife with a force fo much, the greater as the column is longer or more heated. Therefore the tailer we make the chimney, or the hotter we make the fire, the more rapid will be the current, or the draught will be fo much the greater. The afcenfional force is the difference between the weight of the column of heated air in the funnel and a column of the furrounding at mofphere of equal height. We increase the draught, therefore, by increafing the perpendicular height of the chimney. Its length in a horizontal direction gives no increafe, but diminishes the draught by cooling the air before it gets into the funnel. We increase the draught alfo by bringing all the air which enters the chimney very near the fuel; a low mantle-piece will produce this effect, as well as filling up all the fpaces on each fide of the grate. When much air gets in above the fire, by a lofty mantle-piece, the mafs of air in the chimney cannot be much heated. Hence the greatest draught will be produced by bringing down the mantle-piece to the very fuel; but this converts a fire-place into a furnace, and by thus fending the whole air through the fuel, caufes it to burn with great rapidity, producing a prodigious heat: and this producing an increafe of afcenfional force, the current becomes furiously rapid, and the heat and confumption of fuel immenfe. If the fire-place be a cube of a foot and -a half, and the front closed by a door, fo that all the air muft enter through the bottom of the grate, a chimney 15 or 20 feet high, and fufficiently wide to give paffage to all the expanded air which can pafs through the fire, will produce a current which will roar like thunder, and a heat fufficient to run the whole infide into a lump of glass.

But all that is neceffary, in a chamber fireplace, is a current fufficiently great for carrying up the fmoke and vitiated air of the fuel. By allowing a greater quantity of air to get into the chimney, heated only to a moderate degree, we produce a more rapid renewal of the air of the room. But a much smaller renewal of air than we commonly produce is abundantly wholefome and pleafant, and we may have all the pleasure of the light and flame of the fuel at much less expense, by contracting greatly the paffage into the vent. The best way of doing this is by contracting the brick-work on each fide behind the mantle-piece, and reducing it to a narrow parallelogram, having the back of the vent for one of its long fides. Make an iron plate to fit this hole, of the fame length, but broader, fo that it may lie floping, its Jower edge being in contact with the fore fide of the hole, and its upper edge leaning on the back of the vent. In this pofition it shuts the hole entirely. Let the plate have a hinge, and fold up, like the lid of a cheft. In a fire place fit for a room of 14 feet by 18, if this plate be about 18 inches long from fide to fide, and folded back with an inch or an inch and a half of the wall, this will al. low paffage for as much air as will keep up a very

cheerful fire; and by raifing or lowering this GISTER, the fire will burn more or less rap A free paffage of half an inch will be fufficier weather that is not immoderately cold. The which is in the front of the fire, and much wa ed by it, is not allowed to get into the chim where it would be hurried up the vent, but up to the ceiling and is diffufed over the ro This double motion of the air may be cbferve opening a chink of the door and holding a ca in the way. If the candle be held near the f the flame will be blown into the room; bu held near the top of the door, the flame wil blown outward.

The most convenient method of warming apartment in these temperate climates, is by we call a ftove-grate, and the French call a cha from its refemblance to the chapels or oratori the churches. In the great chimney-piece, i a fmaller one fitted up in the fame ftile, but fize no greater than is fufficient for holding fuel. The fides and back of it are made of iron, and are kept at a fmall difiance from fides and back of the main chimney-piece, are continued down to the earth, fo that the pit is alfo feparated. The pipe or chimney of ftove-grate is carried up behind the ornament the mantle-piece till it rifes above the mantle p of the main chimney-piece, and is fitted wi regifter or damper-plate turning round a tranfy axis. The bett form of this regifter is that w we have recommended for an ordinary fire-pl having its axis or joint clcfe at the front; fo when it is opened or turned up, the burn and fmoke ftriking it obliquely, are directed the vent, without any risk of coming out the room. All the reft of it is fhut up by plates or brick-work out of fight. The fuel, being in immediate contact with 'the back fides of the grate, heat them to a great deg and they heat the air contiguous to them. heated air cannot get up the vent, becaufe paffages above thefe fpaces are fhut up. It th fore comes out into the room; fome of it a into the real fire-place and it is carried up vent, and the reft rifes to the ceiling and is fufed over the room.

Lefs than one fourth of the fuel confumed in ordinary fire-place is fufficient to warm a ro and this with the fame cheerful blazing bearth falutary renewal of air.

The various extraneous circumftances, wh impede the current of air in our chimneys produce fmoky houfes, will be treated of, and methods of removing or remedying them, un the article SMOKE. We confider at prefent o the theory of this motion in general, and the difications of its operation arifing from the v ous purposes to which it may be applied, pa cularly by ftoves.

A STOVE in general is a fire-place fhut up all fides, having only a paffage for admitting air to fupport the fire, and a tube for carrying the vitiated air and fmoke; and the air of the ro is warmed by coming into contact with the o fide of the ftove and flue." The general princi of conftruction, therefore, is very fimple. 1 air muft be made to come into as close contac

poffible with the fire, or even to pass through it, and this in fuch quantities as juft to confume a quantity of fuel fufficient for producing the heat required; and the ftove must be fo conftructed, that both the burning fuel and the air which has been heated by it fhall be applied to as extenfive a furface as poffible of furnace, all in contact with the air of the room; and the heated air within the ftove muft not be allowed to get into the funnel which is to carry it off, till it is too much cooled to produce any confiderable heat on the outfide of the ftove.

Our neighbours on the continent, and efpecially towards the north, where the cold of winter is intenfe, and fuel very dear, have beftowed much attention on the conftruction of ftoves, and have combined ingenious economy with every elegance of form. Nothing can be handfomer than the floves of Fayencerie that are to be feen in French Flanders, or the Ruffian ftoves at St Petersburg, finished in ftucco. Here, however, we fhall only confider a ftove in general as a fubject of pneumatical difcuffion, and refer to the article Srove for a farther account of them.

The general form of a ftove, and of which all others are only modifications adapted to circum. ftances of utility or tafte, is as follows.

MIKL (fig. 67, pl. CCLXXXI.) is a quadrangular box of any fize in the direction MI, IK. The infide width from front to back is never lefs than to inches, and rarely extends to 20; the included (pace is divided by partitions. The loweft chamber AB is the receptacle for the fuel, which lies on the bottom of the ftove without any grate: this fire-place has a door AO turning on hinges, and in this door is a very fmall wicket P: the roof of the fire-place extends to within a very few inches of the farther end, leaving a narrow paffage B for the flame. The next partition C' is about 8 inches higher, and reaches alraoft to the other end, leaving a narrow paffage for the flame at C. The partitions D d, Ee, Ff, Gg, Hb, are repeated above, at the diftance of 8 inches, leaving paffages at the ends, alternately difpofed as in the figure; the laft of them, H, communicates with the room vent. This communication may be regulated by a plate of iron, which can be flid acrofs it by a rod or handle which comes through the fide. The more ufual way of fhutting up this paffage is by a fort of pan or bowl of earthen ware, which is whelmed over it with its brim refting in fand contained in a groove formed all round the hole. This damper is introduced by a door in the front, which is then fhut. The whole is fet on low pillars, fo that its bottom may be a few inches from the floor of the room: it is ufually placed in a corner, and the apartments are fo difpofed that their chimneys can be joined in ftacks as with us.

Some ftraw or fhavings of wood are firft burnt on the hearth at its farther end. This warms the air in the ftove, and creates a determined current. The fuel is then laid on the hearth close by the door, and pretty much piled up. It is now kindied; and the current being directed to the vent, there is no danger of any fmoke coming out into the room. To prevent this, the door is shut, and the wicket P opened. The air fupplied by this,

being directed to the middle or bottom of the fuel, quickly kindles it, and the combuftion goes on.

The intention of this construction is obvious. The flame and heated air are retained as long as poffible within the ftove by means of the long paffages; and the narrowness of thefe forces the flame into contact with every particle of foot, fo as to confume it completely, and thus convert the whole combuftible matter of the fuel into heat. For want of this a very confiderable portion of our fuel is wafted by our open fires, even under the very best management: the foot which flicks to our vents is very inflammable, and a pound weight of it will give as much, if not more heat, than a pound of coal. And what fticks to our vents is very inconfiderable, in comparison with what escapes unconfumed at the chimney top. In fires of green wood, peat, and fome kinds of pit-coal, nearly one fifth of the fuel is loft in this way: but in thefe ftoves there is hardly ever any mark of foot to be feen; and even this fmall quantity is produced only after lighting the fires. The volatile inflammable matters are expelled from parts much heated indeed, but not fo hot as to burn; and fome of it charred or half burnt cannot be any further confumed, being enveloped in flame and air already vitiated and unfit for combuftion. But when the ftove is well heated, and the current brifk, no part of the foot escapes the action of the air.

The hot air thus retained in the body of the ftove is applied to its fides in a very extended furface. To increafe this ftill more, the ftove is made narrower from front to back in its upper part; a certain breadth is neceffary below, for fuel. By diminishing their breadth, the proportion of ufeful furface is increased. It is with the fame view of making an extenfive application of a hot furface to the air, that the ftove is not built in the wall, nor even in contact with it, nor with the floor: for by its detached fituation, the air in contact with the back, and the bottom (where it is hotteft), is warmed, and contributes one half of the effect; for the great heat of the bottom makes its effect on the air of the room at leaft equal to that of the two ends. Sometimes a ftove makes part of the wall between two small rooms.

On the whole, the effect of a ftove depends much on keeping in the room the air already heated by it. A fmall open fire in the fame room will be fo far from increafing its beat, that it will greatly diminifh it; it will even draw the warm air from a fuite of adjoining apartments. This is obferved in the houses of the English merchants in St Peterfburgh: their habits of life in Britain make them uneafy without an open fire in their rooms; and this obliges them to beat their ftoves twice a-day, and their houfes are cooler than thofe of the Ruffians, who heat them only once. In many German houses, especially of the lower class, the fire-place of the ftove does not open into the room, but into the yard or a lobby, where all the fires are lighted and tended; whereby is avoided the expence of warm air which muft have been carried off by the ftove; but this must be equally unpleafant and unwholesome.

The directions refpecting ftoves and their conftruction will equally apply to hot walls in gar

dening ;

dening; only particular attention must be paid to the equability of the heat, and the gradation of it in different parts of the building. The heat in the flue gradually diminishes as it recedes from the fire-place. It must therefore be fo conducted through the building by frequent returns, that in every part there may be a mixture of warmer and cooler branches of the flue, and the final chimney fhould be close by the fire-place. If it is the flue of a greenhouse, it is beft to allow the flue to proceed gradually up the wall in its different returns, by which the loweft part will be the warmest, and the heated air will afcend among the pots and plants. In the hypocaufta and sudaria of the ancient Greeks and Romans, the flue was conducted chiefly under the floors. See HYPOCAUSTUM. Malt-kilns are a species of stove which merit attention. Many attempts have been made to improve them on the principle of flue ftoves; but they have been unfuccefsful, because heat is not what is chiefly wanted in malting; it is a copious current of very dry air to carry off the moisture. We refer the examination of this subject alfo to the article STOVE, and proceed to confider the current of heated air in the chief varieties of furnaces.

All that is to be attended to in the different kinds of melting furnaces is, that the current of air be fufficiently rapid, and that it be applied in as extenfive a furface as poffible to the fubftance to be melted. The more rapid the current it is the hotter, because it is confuming more fuel; and therefore its effect increases in a higher proportion than its rapidity. It is doubly effectual if twice as hot; and if it then be twice as rapid, there is twice the quantity of doubly hot air applied to the fubject; it would therefore be four times more powerful. This is procured by raifing the chimney of the furnace to a greater height. The clofe application of it to the fubject can hardly be laid down in general terms, because it depends on the precife circumftances of each cafe.

In reverberatory furnaces, fuch as refining furnaces for gold, filver, and copper, the flame is made to play over the surface of the melted metal. This is produced entirely by the form of the furnace, by making the arch as low as the circumftances will allow. (See CHEMISTRY, Index; and FURNACE, 15.) Experience has taught the chief circumftances of their conftruction, viz. that the fuel fhould be at one end on a grate, through which the air enters to maintain the fire; and that the metal fhould be placed on a level floor between the fuel and the chimney which produces the current. But there is no kind of furnace more variable in its construction and effects. This has occafioned many whimfical varieties in their form. This uncertainty feems to depend much on a circumstance seldom taken notice of by mineralogi. cal writers. It is not heat alone that is wanted in the refining of filver by lead, for instance. We muft make a continual application to its furface of air which has not contributed to the combuftion of the fuel. Any quantity of the hottest air, already faturated with the fuel, may play on the furface of the metal for ever, and keep it in the state of moft perfect fufion, but without refining it. Now, in the ordinary conftruction of a fur. nace, this is much the cafe. If the whole air has

come in by the grate, and paffed through the middle of the fuel, it must be nearly faturated with it; and if air be alfo admitted by the door (which is generally done), the pure air lies above the vi tiated air, and during the paffage along the hori zontal part of the furnace and the furface of the metal, it ftill keeps above it. Thus the metal does not come into contact with air fit to act on the bafe metal and calcine it, and the operation of refining goes on flowly. Trifling circumftances in the form of the arch or canal may tend to promote the jumbling of the airs together, and thus render the operation more expeditious; and as thefe are but ill understood, they are confidered as fo many noftrums of great importance. Changes in the form of the roof fhould therefore be tried, directed to this circumstance.

The glafs-houfe furnace exhibits the chief va riety in the management of the current of heated air. (See GLASS-MAKING, Se&. IV.) In this it is neceffary that the hole at which the workman dips his pipe into the pot fhall be as hot as any part of the furnace. This could not be the cafe, if the furnace had a chimney above the dipping hole; as in this cafe cold air would immediately rush in. To prevent this, the hole is made the chimney; but as this would be too fhort, and would produce very little current and very little heat, the whole furnace is fet under a tall dome. Thus the heated air from the real furnace is confined in this dome, and constitutes a high column of very light air, which therefore rifes with great force up the dome, and escapes at the top. The dome is therefore the chimney, and will produce a current proportioned to its height. Some are raifed above ico feet. When all the doors are shut, and no fupply given except through the fire, the current and heat become prodigious. But the workmen being in this chimney, they must have refpirable air. Yet notwithstanding this fupply by the house doors, the draught of the real furnace is vaftly increased by the dome, and a heat produced fufficient for the work, which could not be produced without the dome.

This has been applied with great ingenuity and effect to a furnace for melting iron from the ore, and an iron finery, both without a blast. The common blaft iron furnace is well known. It is a tall cone with the apex undermoft. The ore and fluxes are thrown into this cone, mixed intimately with the fuel, till it is full, and the blaft of moft powerful bellows is directed into the bottom of this cone through a hole in the fide. The air is thrown in with fuch force, that it makes its way through the mass of matter, kindles the fuel in its paffage, and fluxes the materials, which then drop down into a receptacle below the blaft-hole, and thus the paffage for the air is kept unobstructed. It was thought impoffible to produce or maintain this current without bellows; but Mr Cotterel, an ingenious founder, tried the effect of a tall dome placed over the mouth of the furnace; and though it was not half the height of many glafs house domes, it had the defired effect. It is extremely difficult to place the holes below, at which the air is to enter, at fuch a precise height as neither to be choked by the melted matter, nor to leave ore and ftones below them unmelted;

but