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during the whole of the returning stroke, and at the end of it the machine has acquired its greatest velocity. Now the working stroke begins, and the overplus of power is at an end. The machine accelerates no more; but if the power is just in equilibrio with the resistance, it keeps the velocity which it has acquired, and is still more acceleratcd during the next returning stroke. But now, at the beginning of the subsequent working stroke, there is an overplus of resistance, and a retardation begins, and continues during the whole rise of the piston; but it is considerable in comparison of what it would have been without the fly; for the fly, retaining its acquired momentum, drags forward the rest of the machine, aiding the impelling power of the wheel. It does this by all the communications taking into each other in the opposite direction. The teeth of the intervening wheels are heard to drop from their former contact on one side, to a contact on the other. By considering this process with attention, we easily perceive that, in a few strokes, the overplus of power during the returning stroke comes to be so adjusted to the deficiency during the working stroke, that the accelerations and retardations exactly destroy each other, and every succeeding stroke is made with the same velocity, and an equal number of strokes is made in every succeeding minute. Thus the machine acquires a general uniformity with periodical inequalities. It is plain, that by sufficiently enlarging either the diameter or the weight of the fly, the irregularity of the motion may be rendered as small as we please, It is much better to enlarge the diameter. This preserves the friction more moderate, and the pivot wears less. For these reasons, a fly is in general a considerable improvement in machinery, by equalising many exertions that are naturally very irregular. Thus, a man working at a common windlass exerts a very irregular pressure on the winch. In one of his positions in each turn he can exert a force of near 70 pounds without fatigue, but in another he cannot exert above 25; nor must he be loaded with much above this in general. But if a large fly be connected properly with the windlass, he will act with equal ease and speed against 30 pounds.

This regulating power of the fly is without bounds, and may be used to render uniform a motion produced by the most desultory and irregular power. It is thus that the most regular motion is given to mills that are driven by a single-stroke steam engine, where for two or even three seconds there is no force pressing round the mill. The communication is made through a massive fly of very great diameter, whirling with great rapidity. As soon as the impulse ceases, the fly, continuing its motion, urges round the whole machinery with almost unabated speed. At this instant all the teeth, and all the joints, between the fly and the first mover, are heard to catch in the opposite direction.

in the Albion mills, a heavy fly was added with great propriety; for if the mills had been regulated by their millstones only, then at every change of stroke in the steam engine, the whole train of communications between the beam, which is the first mover, and the regulating millstone, which is the very last mover, would take in the opposite direction. Although each drop in the teeth and joints be but a trifle, the whole, added together, would make a considerable jolt. This is avoided by a regulator immediately adjoining to the beam. This continually presses the working machinery in one direction. So judiciously were the movements of that noble machine contrived, and so nicely were they executed, that not the least noise was heard, nor the slightest tremor felt in the building.

Mr. Valoué's beautiful pile engine employed at Westminster Bridgeisanother remarkable instance of the regulating power of a fly. When the ram is dropped, and its follower disengaged immediately after it, the horses would instantly tumble down, because the load, against which they had been straining hard, is at once taken off; but the gin is connected with a very large fly, which checks any remarkable acceleration, allowing the horses to lean on it during the descent of the load; after which their draught recommences immediately. The spindles, cards, and bobbins, of a cotton mill, are also a sort of flies. Indeed all bulky machines of the rotative kind tend to preserve their motion with some degree of steadiness, and their great momentum of inertia is as useful in this respect as it is prejudicial to the acceleration or any reciprocation when wanted.

There is another kind of regulating fly, consisting of wings whirled briskly round till the resistance of the air prevents any great acceleration. This is a very bad one for a working machine, for it produces its effect by really wasting a part of the moving power. Frequently it employs a very great and unknown part of it, and robs the proprietor of much work. It should never be introduced into any machine employed in manufac

tures.

Some rare cases occur where a very different regulator is required: where a certain determined velocity is found necessary. In this ease the machine is furnished, at its extreme mover, with a conical pendulum, consisting of two heavy balls hanging by rods, which move in very nice and steady joints at the top of a vertical axis. It is well known, that when this axis turns round, with an angular velocity suited to the length of those pendulums, the time of a revolution is determined. Thus, if the length of each pendulum be 591 inches, the axis will make a revolution in two seconds very nearly. If we attempt to force it more swiftly round, the balls will recede a little from the axis, but it employs as long time for a revolution as before; and we cannot make it turn swifter, unless the impelling power be increased beyond all probability; in which case the pendulum will fly out from the centre till the rods are horizontal, after which every increase of power will accelerate the machine very sensibly. Watt and Boulton have applied this contrivance with great ingenuity to their steam engines, when they are employed for driving machinery for manufac Many machines include in their construction. tures which have a very changeable resistance,, movements which are equivalent to this inten- and where a certain speed cannot be much detional regulator. A flour mill, for example, can- parted from without great inconvenience. They not be better regulated than by its millstone; but, have connected this recess. of the balls from the

If any permanent change should happen in the impelling power, or in the resistance, the fly makes no obstacle to its producing its full effect on the machine, and it will be observed to accelerate or retard uniformly, till a new general speed is acquired exactly corresponding with this new power and resistance.

axis (which gives immediate indication of an increase of power or a diminution of resistance) with the cock which admits the steam to the working cylinder. The balls flying out cause the cock to close a little, and diminish the supply of steam. The impelling power diminishes the next moment, and the balls again, approach the axis, and the rotation goes on as before, although there may have occurred a very great excess or deficiency of power.

A

FLY’BOAT. s. (fly and boat.) A kind of vessel nimble and light for sailing. FLYCATCHER. s. (fly and catch.) One that hunts flies (Dryden).

One that flies or runs away (Sandys). 2. One FLY'ER. s. (from fly.) See FLIER. 1. that uses wings. 3. The fly of a jack.

FLYERS, in architecture, such stairs as go straight, and do not wind round, nor have the steps made tapering; but the ends, and the fore and back part of each stair, respectively parallel.

A fly is sometimes employed for a very different purpose from that of a regulator of motionit is employed as a collector of power. Suppose all resistance removed from the working point of a machine furnished with a very large or heavy fly immediately connected with the working point. When a small force is applied to the impelled point of this machine, motion will begin in the machine, and the fly begin to turn. Continue to press uniformly, and the machine will accelerate. This may be continued till the fly has acquired a very rapid motion. If at this moment a resisting body be applied to the working point, it will be acted on with very great force; for the fly has now accumulated in its circumference a very great momentum. If a body were exposed immediately to the action of this circumference, it would be violently struck. Much more will it be so, if the body be exposed to the action of the working point, which perhaps makes one turn while the fly makes a hundred. It will exert a hundred times more force there (very nearly) than at its own circumference. All the motion which has been accumulated on the fly during the whole progress of its acceleration is exerted in an instant at the working point, multiplied by the momentum depending on the proportion of the parts of the machine. It is thus that the coining press performs its office; nay, it is thus that the blacksmith forges a bar of iron. Swinging the great sledge hammer round his head, and urging it with force the whole way, this accumulated motion is at once extinguished by impact on the iron. It is thus also we drive a nail, &c. This accumulating power of a fly has occasioned many to imagine that a fly really adds power or mechanical force to an engine; and, not understanding on what its efficacy depends, they often place the fly in a situation where it only adds a useless burden to the machine. It should always be made to move with rapidity. If intended for a mere regulator, it should be near the first mover; and if it be intended to accumulate force in the working point, it should not be far separated from it. In a certain sense, a fly may be said to add power to a machine, because by accumulating into the exertion of one moment the exertions of many, we can sometimes overcome an obstacle that we never could have balanced by the same machine unaided by the fly. And it is this accumulation of force which gives such an appearance of power to some of our first movers.

FLY, in the sea language, that part of the mariner's compass on which the several winds or points are drawn. "Let fly the sheet," is a word of command to let loose the sheet, in case of a gust of wind, lest the ship should overset, or spend her top-sails and masts; which is prevented by letting the sheet go a-main, that it may hold no wind.

To FLY BLOW. v. a. (fly and blow.) To taint with flies; to fill with maggots (Still.).

To FLY FISH. v. n. (fly and fish.) To angle with a hook baited with a fly.

FLYING, the progressive motion of a bird, parts of birds chiefly concerned in flying are or other winged animal, in the liquid air. The the wings, by which they are sustained or wafted along. The tail, Messieurs Willoughby, Ray, and many others, imagine to be principally employed in steering and turning the body in the air, as a rudder: but Borelli has put it beyond all doubt, that this is the least use of it, which is chiefly to assist the bird in its ascent and descent in the air; and to obviate the vacillations of the body and wings: for, as to turning to this or that side, it is formed by the wings, and inclinations of the body, and but very little by the help of the tail. The flying of a bird, in effect, is quite a different thing from the rowing of a vessel. Birds do not vibrate their wings towards the tail, as them downwards: nor does the tail of the bird oars are struck towards the stern, but waft cut the air at right angles, as the rudder does the water; but is disposed horizontally, and preserves the same situation what way soever the bird turns.

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In effect, as a vessel is turned about on its centre of gravity to the right, by a brisk application of the oars to the left, so a bird in beating the air with its right wing alone, towards the tail, will turn its fore part to the left. Thus pigeons, changing their course to the left, the other almost at rest. Birds of a long neck would labour it with their right wing, keeping alter their course by the inclinations of their head and neck, which altering the course of the line of gravity, the bird will proceed in a new direction.

The general mode of flying is this: the bird first bends his legs, and springs with a violent leap from the ground; then opens and expands the joints of his wings, so as to make a right line perpendicular to the sides of his body: thus the wings, with all the feathers therein, constitute one continued lamina. Being now raised a little above the horizon, and vibrating the wings with great force and velocity perpendicularly against the subject air, that fluid resists those succussions, both from its natural inactivity and elasticity, by means of which the whole body of the bird is protruded. The resistance the air makes to the withdrawing of the wings, and consequently the progress of the bird, will be so much the greater, as the waft or stroke of the fan of the wing is longer: but as the force of the wing is continually di

minished by this resistance, when the two forces come to be in equilibrio, the bird will remain suspended in the same place: for the bird only ascends so long as the arch of air the wing describes makes a resistance equal to the excess of the specific gravity of the bird above the air. If the air, therefore, is so rare as to give way with the same velocity as it is struck with, there will be no resistance, and consequently the bird can never mount. Birds never fly upwards in a perpendicular line, but always in a parabola. In a direct ascent, the natural and artificial tendency would oppose and destroy each other, so that the progress would be very slow. In a direct descent they would aid one another, so that the fall would be too precipitate.

FLYING-FISH, in ichthyology. See Exo

COETUS.

FLYING PINION, is part of a clock, having a fly or fan by which to gather air, and so bridle the rapidity of the clock's motion when the weight descends in the striking part.

FO. See FE.

FOAL, the produce of a horse and mare in a general sense; though more usually applied to the colt or male produce; the female being commonly called a filly foal. It is said to be no difficult matter to know the shape that a foal is likely to be of when full grown; for the same shape that he carries at a month he will carry at six years old, if he be not abused in after keeping; and as the good shape, so will be the defects also. As to the height, it is observed, that a large shin-bone, long from the knee to the pastern, indicates a tall horse. Another way of judging is, to see what space he has between his knee and withers; which being doubled, it will be his height when he is a competent horse. There are also means to know the probable goodness of foals in a subsequent period; for if they be stirring, not apt to be frighted, active, and striving for mastery, some writers assert, they generally prove good mettled horses.

FOAL-TEETH. See the article AGE. To FOAL. v. a. (from the noun.) To bring forth a foal (May).

FOAM. s. (ram, Saxon.) The white substance which agitation or fermentation gathers on the top of liquors; froth; spume (Ho

sea).

To FOAM. v. n. (from the noun.) 1. To froth; to gather foam (Shakspeare). 2. To be in rage; to be violently agitated (Mark).

FO'AMY. a. (from foam.) Covered with foam; frothy (Sidney).

FOB. s. (fuppe, German.) A small pocket (Addison).

To Foв. v. a. (fuppen, German.) 1. To cheat; to trick; to defraud (Shakspeare). 2. To FOB off. To shift off; to put aside with an artifice (Addison).

FO'CAL. a. (from focus, Latin.) Belonging to the focus (Denham).

FOCAL DISTANCE, the distance of the focus, which is sometimes understood as its distance from the vertex, as in the parabola; and

sometimes its distance from the centre, as in the ellipse or hyperbola.

FO-CHAN, a village of China, in the province of Quangtong. It is called a village, because it has no walls nor a presiding governor, although it has a great trade, and contains more houses and inhabitants than Canton. It is reckoned to be nine miles in circumference, and to contain 1,000,000 inhabitants. It is 12 miles from Canton.

FOCHIA NOVA, a seaport of Natolia, with a good harbour, and a castle. It is seated on the gulf of Sanderly. Lat 38. 44 N. Lon. 26. 39 E.

FOCIL. s. (focile, French.) The greater or less bone between the knee and ankle, or elbow and wrist (Wiseman).

FOCILLATION. s. (focillo, Lat.) Comfort; support.

FOCOSO, in music, with fire and spirit.

FOCUS, in geometry and the conic sections, is applied to certain points in the ellipse, hyperbola, and parabola, where the rays reflected from all parts of these curves do concur or meet; that is, rays issuing from a luminous point in the one focus, and falling on all points of the curves, are reflected into the other focus, or into the line directed to the other focus, viz. into the other focus in the ellipse and parabola, and directly from it in the byperbola. Which is the reason of the name focus, or burning-point. Hence, as the one focus of the parabola is at an infinite distance; and consequently all rays drawn from it, to any finite part of the curve about the vertex, are parallel to one another; therefore if rays from the sun, or any other object so distant as that those rays may be accounted parallel, fall upon the curve of a parabola or concave surface of a paraboloidal figure, those rays will all be reflected into its focus.

In all the three curves the double ordinate drawn through the focus is the parameter of the axis, or a third proportional to the transverse and conjugate. If there be any tangent to these curves, and two lines drawn from the foci to the point of contact, these two lines will make equa! angles with that tangent.

In the parabola, the distance from the focus to the vertex is equal to of the parameter, or the ordinate at the focus.

For other properties of the foci, see the different authors on Conics.

Focus, in optics, is a point in which several rays meet, and are collected, after being either reflected or refracted. It is so called, because the rays being here brought together and united, their force and effect are increased, insomuch as to be able to burn; and therefore it is that bodies are placed in this point to be burnt, or to shew the effect of burning glasses, or mirrors. It is to be observed, however, that in practice, the focus is not an absolute point, but a space of some small breadth, over which the rays are scattered; owing to the different nature and refrangibility of the rays of light and to the imperfections in the

figure of the lens, &c. However, the smaller this space is, the better, or the nearer to perfection the machine approaches. Huygens shews that the focus of a lens convex on both sides, has its breadth equal to of the thickness of the lens.

Virtual Focus, or Point of Divergence, so called by Mr. Molyneux, is the point from whence rays tend, after refraction or reflection; being in this respect opposed to the ordinary focus, or point of concurrence, where rays are made to meet after refraction or reflection. Thus, the foci of an hyperbola are mutually virtual foci to each other: but, in an ellipse, they are common foci to each other: for the rays are reflected from the other focus in the hyperbola, but towards it in the ellipse. Practical Rules for finding the Foci of

Glasses.

1. To find, by experiment, the focus of a convex spherical glass, being of a small sphere; apply it to the end of a scale of inches and decimal parts, and expose it before the sun; upon the scale may be seen the bright intersection of the rays measured out: or, expose it in the hole of a dark chamber; and where a white paper receives the distinct representation of distant objects, there is the focus of the glass. 2. For a glass of a pretty long focus, observe some distant object through it, and recede from the glass till the eye perceives all in confusion, or the object begins to appear inverted; then the eye is in the focus. 3. For a plano-convex glass: make it reflect the sun against the wall; on the wall will then be seen two sorts of light, a brighter within another more obscure: withdraw the glass from the wall, till the bright image be in its least dimensions; then is the glass distant from the wall about a fourth part of its focal length. 4. For a double convex: expose cach side to the sun in like manner; and observe both the distances of the glass from the wall: then is the first distance about half the radius of the convexity turned from the sun; and the second is about half the radius of the other convexity. The radii of the two convexities being thus known, the focus is then found by this rule; As the sum of the radii of both convexities is to the radius of either convexity so is double the radius of the other convexity to the distance of the focus.

Dr. Halley gave general methods of finding the foci of all kinds of glasses, both geometrically and algebraically. See Phil. Trans. No. 205, &c. The same is also shewn by the principal writers on optics; as by Emerson, Martin, Smith, Wood, &c. See also our articles CATOPTRICS and DIOPTRICS.

FODDER. s. (Foðre, foder, Saxon.) Dry food stored up for cattle against winter (Knolles).

To Fo'DDER. v. a. (from the noun.) To feed with dry food (Evelyn).

FODDERER. s. He who fodders cattle. FODWAR, a town of Hungary. Lat. 46. 39 N. Lon 19. 36 E.

FOE. s. (pah, Saxon.) 1. An enemy in

war (Spenser). 2. A persecutor; an enemy in common life. 3. An opponent; an ill wisher (Watts).

FO'EMAN. s. (from foe and man.) Enemy in war; antagonist: obsolete (Spenser). FOENICULUM. (fæniculum, quasi fœnum osulorum, the hay or herb good for the sight; so called because it is thought good for the eyes.) Fennel. See ANETHUM.

FENICULUM AQUATICUM. Water fennel. Fine-leaved water hemlock. The plant which bears this name in the pharmacopoeias is the phellandrium aquaticum; foliorum ramificationibus divaricatis, of Linnéus. It possesses vertiginous and poisonous qualities, which are best counteracted by acids, after clearing the primæ viæ. The seeds are recommended by some, in conjunction with peruvian bark, in the cure of pulmonary phthisis. See PHELLANDRIUM.

FENICULUM DULCE. Common fennel. Anethum fœniculum fructibus ovatis of Linnéus. Class pentandria. Order digynia. The seeds and roots of this indeginous plant are di rected by the colleges of London and Edinburgh. The seeds have an aromatic smell, and a warm sweetish taste, and contain a large proportion of essential oil. They are stomachic and carminative. The root has a sweet taste, but very little aromatic warmth, and is said to be pectoral and diuretic.

FONICULUM PORCINUM. DANUM and ANETHUM.

See PEUCE

FONICULUM VULGARE. Common fennel or fenckle. A variety of the anethum fœniculum. See FaNICULUM DULCE.

FŒNUGREEK, in botany. See TRIGO

NELLA.

FOENUM GRÆCUM. (færum, hay, and gracus, belonging to Greece, because_in Greece it grew in the meadows like hay.) Fenugreek. Trigonella foenum græcum leguminibus sessilibus strictis erectiusculis subfalcatis acuminatis, caule erecto, of Linnéus. Diadelphia. Decandria. A native of Montpelier. The seeds are brought to us from the southern parts of France and Germany; they have a strong disagreeable smell, and an unctu ous farinaceous taste, accompanied with a slight bitterness. They are esteemed as assisting the formation of pus in inflammatory tumours; and the meal, with that intention, is made into a poultice with milk; though the meal of linseed is at present more frequently resorted to, as a better emollient and sedative. FOENUM CAMELORUM. See JUNCUS ODORATUS.

FOETIDIA. In botany, a genus of the class icosandria, order monogynia. Calyx superior, four-cleft; corolless; capsule woody, four-celled; the cells one or two-seeded. A tree of Mauritius, with one-flowered terminal peduncles.

FOETUS. (fœtus.) The child enclosed in the uterus of its mother is called a fœtus from the fifth month after pregnancy until the time of its birth. This term should rather be spelt fetus, as derived from the old Latin feo, whence fio, and is so spelt by all the old

Roman writers. From the same root we obtain fecundus, femen, femina. The internal parts peculiar to the foetus are the thymus gland, canalis venosus, canalis arteriosus, foramen ovale, and the membrana pupillaris. Besides these peculiarities, there are other circumstances in which the foetus differs from the adult. The lungs are black and collapsed, and sink in water; the liver is very large; all the glands, especially the thymus and suprarenal, and the vermiform process of the cæcum, are also considerably larger in proportion, The teeth of the foetus are hid within their sockets; the great intestines contain a substance called meconium; the membrana tympani is covered with a kind of mucous membrane, and the bones in many places are cartilaginous.

FOG, or MIST, a meteor, consisting of gross vapours, floating near the surface of the earth. Mists, according to lord Bacon, are imperfect condensations of the air, consisting of a large proportion of the air, and a small one of the aqueous vapour: and these happen in the winter, about the change of the weather from frost to thaw, or from thaw to frost; but in the summer, and in the spring, from the expansion of the dew. If the vapours, which are raised plentifully from the earth and waters, either by the solar or subterraneous heat, do at their first entrance into the atmosphere meet with cold enough to condense thein to a considerable degree, their specific gravity is by that means increased, and so they will be stop ped from ascending; and either return back in form of dew or of drizzling rain, or remain suspended some time in the form of a fog. Vapours may be seen on the high grounds as well as the low, but more especially about marshy places. They are easily dissipated by the wind, as also by the heat of the sun. They continue longest in the lowest grounds, be cause those places contain most moisture, and are least exposed to the action of the wind. Hence we may easily conceive, that fogs are only low clouds, or clouds in the lowest region of the air; as clouds are no other than fogs raised on high. (See CLOUD.) When fogs stink, then the vapours are mixed with sulphureous and offensive exhalations. Objects viewed through fogs appear larger and more remote than through the common air. Mr. Boyle observes that, upon the coast of Coromandel, and most maritime parts of the East Indies, there are, notwithstanding the heat of the climate, annual fogs, so thick, as to occasion people of other nations who reside there, and even the more tender sort of the natives, to keep their houses close shut up. Fogs are commonly pretty strongly electrified, as appears from Mr. Cavallo's experiments upon

them.

FOG. s. (fogagium, low Latin.) Aftergrass. FOGGILY. ad. (from foggy.) Mistily; darkly; cloudily.

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FOGLIETA (Uberto), a Genoese priest, born in 1518. He was banished from his native country for the freedom of his writings. He then retired to Rome, where he died in 1581. His principal works are, 1. Historia Genuensium, 1585. 2. De Causa Magnitu dinis Turcarum Imperii, 3. Della Republica di Genoa. FOGO. See FUEGO.

FOH! An interjection of abhorrence.

FO-HI, the first Chinese monarch, who is said to have founded that kingdom 200 years after the deluge. He removed the seat of the empire from the province of Xen Si to Chin Cheu. To him the Chinese are indebted for musical instruments, a code of laws, the regulation of the sexual intercourse, which before him was promiscuous, and for religious observances. He is said to have reigned 115 years, but so much fable is blended with his story, that it is not proper to mention more concerning him.

FOIBLE. s. (French.) A weak side; a blind side; a failing (Freind).

To FOIL. v. a. (affoler, old French.) 1. To put to the worst; to defeat (Milton). 2. (fouiller, French.) To blunt; to dull (Shakspeare). 3. To defeat; to puzzle (Addison).

FOGGINESS. s. (from foggy.) The state of being dark or misty; cloudiness; mistiness. FOGGY. a. (from fog.). Misty; cloudy; dark (Evelyn). 2. Cloudy in understanding;

dull.

1. A defeat; a

FOIL. s. (from the verb.) miscarriage (Southern). 2. Leaf gilding. (feuille, French.) (Milton). 3. Something of another colour near which jewels are set to raise their lustre (Sidney). 4. A blunt sword used in fencing (Shakspeare).

FOIL, a term used in hare hunting. When, during the chase, a hare, after a head or dou ble, runs over the ground she has run before, she is then said to be running the foil, and with strict truth; as nothing can so much foil the hounds as a chase of this description. Old hares, who have speed enough to break away, and get considerably a-head, almost invariably throw themselves out to the right or left, double, and quat; particularly if a hedge-row, hedge, fern, furze, or any kind of covert presents itself favourably for the purpose. The hounds continuing to run the scent to the spot where she made her head, over-run the hare, and having no continuance of scent, are necessarily at fault; during which delay of trying forward, trying back, making a cast to the right, then a cast to the left, the hare slips into her foil; by which repeated runnings, she often obtains an escape she could obtain in no other way.

FOILER. s. (from foil.) One who has gained advantage over another.

To FOIN. v. n. (foindre, Fr. Skinner.) To push in fencing (Dryden).

ForN. s. (from the verb.) A thrust; a

push.

FOISON. s. (Foiron, Saxon.) Plenty; abundance out of use (Shakspeure).

To FOIST. v. a. (fausser, French.) To insert by forgery (Carew).

FOISTINESS. s. (from foisty.) Fustiness; mouldiness (Tusser).

FOISTY. a. (See FUSTY.) Mouldy; fusty.

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