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for the thermometer fwells as long as it continues to abforb fentible heat from the water: and when the fenfible heat in both is in equilibrio, in a proportion depending on the nature of the two fluids, the thermometer rifes no more, because it absorbs no more heat or fire from the water; for the particles of water which are in immediate contact with the bottom, are now (by this gradul expanfion of liquidity) at fuch diftance from each other, that their laws of attraction for each other and for heat are totally changed. Each particle either no longer attracts, or perhaps it repels its adjoining particle, and now accumulates round itfelf a great number of the particles of heat, and forms a particle of elaftic Ruids fo related to the adjoining new formed particles, as to repel them to a dif. tance at least 100 times greater than their diftances in the state of water. Thus a mafs of elaftic vapour of fenfible magnitude is formed. Being at leaft ro,000 times lighter than an equal bulk of water, it must rife up through it, as a cork would do, in form of a transparent ball or bubble, and getting to the top, it diffipates, filing the upper part of the vellel with vapour or team. Thus, by toffing the liquid into bubbles, which are produced all over the bottom and fides of the veffel, it produces the phenomenon of ebullition or beiting. Obferve, that during its paffage up through the water, it is not changed or condenfed; for the furrounding water is already fo hot that the fenfible or uncombined heat in it, is in equilibrio with that in the vapour, and therefore it is not difpofed to abforb any of that heat which is combined as an ingredient of this vapour, and gives it its elafticity. For this reafon, it happens that water will not boil till its whole mafs be heated up to 212°; for if the upper part be colder, it robs the rifing bubble of that heat which is neeef fary for its elasticity, fo that it immediately col lapfes again, and the furface of the water remains it. This may be perceived by holding water in a Florence flak over a lamp or choffer. It will be obferved, fome time before the real ebullition, that fome bubbles are formed at the bottom, and get up a very little way, and then difappear. The diftances which they reach before coilapfing increafe as the water continues to warm farther up the mafs, till at laft it breaks out into boiling. If the handle of a tea kettle be grafped with the hand, a tremor will be felt for fome little time before boiling, arifing from the little fuccuflions which are produced by the collapfing of the bubbles of vapour. This is much more violent, and is really a remarkable phenomenon, if we fuddenly plunge a lump of red hot iron into a vessel of cold water, taking care that no red part be near the furface. If the hand be now applied to the fide of the veffel, a most violent tremor is felt, and fometimes ftrong thumps: thefe arife from the collapfing of very large bubbles. If the upper part of the iron be too hot, it warms the furrounding water so much, that the bubbles from below come up through it uncondenfed, and produce ebullition without this fuccuflion. The great refemblance of this tremor to the feeling which we have during the fhock of an earthquake has led many to fuppofe that thefe laft are produced in the fame way, (See EARTHQUAKE,

22); but their hypothefis, for the objections there stated to it, feems totally untenable. It is owing to a fimilar caufe, however, that violent thumps are fometimes felt on the bottom of a tea-kettle, especially one which has been long in ufe. Such are frequently crufted on the bottom with a stony concretion. This fometimes is de tached in little feales. When one of thefe is adhering by one end to the bottom, the water gets between them in a thin film. Fere it may be heated confiterably above the boiling temperature, and it fuddenly ifes up in a large bubble, which collapfes immediately. A fmooth thilling lying on the bottom wil produce this appearance very violentiy, or a thimble with the mouth down. To make water boil, the fire must be applied to' the bottom or fides of the veffel. If the heat be applied at the top of the water, it will waste away without boiling; for the very fuperficial par ticles are firft fupplied with the heat neceflary for rendering them elastic, and they fly off without agtating the reft. Since this difengagement of va pour is the effect of its elafticity, and fince this elafticity is a determined force when the temperature is given, it follows, that fluids cannot boil till the eiafticity of the vapour overcomes the preffure of the incumbent fluid and of the atmofphere. Therefore, when this preffure is removed or diminished, the fluids must sooner overcome what remains, and boil at a lower tempera ture. According y it is obferved that water will boil in an exhaufted receiver when of the heat of the human body. If two glass balls A and B, (fig, 1. Pl. 319.) be connected by a fler der tube,. and one of them A be filled with water (a small opening or pipe b being left at top of the other), and this be made to boil, the vapour produced' from it will drive ali the air out of the other, and will at laft come out itself, producing fteam at the mouth of the pipe. When the ball B is obferved to be occupied by tranfparent vapour,. we may conclude that the air is completely expelled. Now fliut the pipe by flicking it into a piece of tallow or bees-wax; the vapour in B will foon condenfe, and there will be a vacuum. The flame of a lamp and blow pipe being directed to the little pipe, will caufe it immediately to clofe and feai hermetically. We now have a pretty instrument called: a PULSE GLASS. Grafp the ball A in the hollow of the hand; the heat of the hand will immediately expand the bubble of vapour which may be in it, and this vapour will drive the water into B, and then will blow up through it for a long while, keeping it in a state of violent ebullition, as long as there remains a drop or film of water in A. But care must be taken that is all the while kept cold, that it may condense the vapour as faft as it rifes through the water. Touching B with the hand, or breathing warm on it, will immediately stop the ebullition in it. When the water in A has thus been diffipated, grasp B in the hand; the water will be driven into A, and the cbuilition will take place there as it did in B. Putting one of the balls into the mouth will make the ebullition more violent in the other, and the one in the mouth will feel very coid. This is a pretty illuf tration of the rapid forption of the heat by the particles of water which are thus converted into

elaftic

elaftic vapour. We have feen this little toy fuf- MATICS we took notice of it as fomething like a pended by the middle of the tube like a balance, natural law, that all these airs, or gafes, had their and thus placed in the infide of a window, having elafticity very nearly, if not exactly proportionali two holes a and b cut in the pane, in fuch a fitua. to their density. This appears from the experition that when A is full of water and preponde- ments of Achard, of Fontana, and others, on virates, B is oppofite to the hole b. Whenever the tal air, inflammable air, fixed air, and fome oroom became fufficiently warm, the vapour was thers. It gives us fome prefumption to fuppofe formed in A, and immediately drove the water that it holds in all elaftic vapours whatever, and into B, which was kept cool by the air coming that it is connected with their elafticity; and it into the room through the hole b. By thefe means renders it fomewhat probable that they are all eB was made to preponderate in its turn, and A laftic, only because the caufe of heat (the matter was then opposite to the hole a, aud the procefs of fire if you will) is claftic, and that their law of was now repeated in the oppofite direction; and elaticity, in refpect of denity, is the fame with this amufement continued as long as the room that of fire. But it must be obferved, that alwas warm enough. though we thus affign the elafticity of fire as the immediate caufe of the e.afticity of vapour, in the fame way, and on the fame grounds, that we a fcribe the fluidity of brine to the fluidity of the water which holds the folid falt in folution, it does not follow that this is owing, as is common. ly fuppofed, to a repulfion or tendency to recede from each other exerted by the particles of fire. We are as much entitled to infer a repulsion of unlimited extent between the particles of water for we fee that by its means a fingle particle of fea-falt becomes diffeminated through the whole of a very large veffel. If water had not been a vifibie and palpable substance, and the Git only had been visible and palpable, we might have formed a fimilar notion of chemical folution. But we, on the contrary, have considered the quaquaverfum motion or expantion of the falt as a dile mination among the particles of water; and we have afcribed it to the ftrong attraction of the atoms of falt for the atoms of water, and the attraction of these laft for each other, thinking that each atom of falt accumulates round ittelf a multitude of watery atoins, and by fo doing muft refide from the other faline atoms. Nay, we farther fee, that by forces which we naturaliy confiler as attractions, an expanfion may be produced of the whole mafs, which will act against external mechanical forces. It is thus that wood fwells with almost infuperable force by imbibing moisture; it is thus that a sponge immersed in was ter becomes really an elaftic compreffible body, refembling a blown bladder; and there are appearances which warrant us to apply this mode of conception to elaftic fluids. When air is fud denly compreffed, a thermometer included in it fhows a rife of temperature; that is, an appearance of heat now redundant which was formerly combined. The heat feems to be squeezed out as the water from the fponge. Accordingly this opinion, that the elafticity of fteam and other va pours is owing merely to the attraction of fire, and the confequent diffemination of their parti cles through the whole mafs of fire, has been entertained by many naturalifts, and it has been afcribed entirely to attraction. We by no means pretend to decide; but we think the analogy by far too fight to found any confident opinion on it. The aim is to folve phenomena by attraction. only, as if it were of more ealy conception than repulfion. Confidered merely as facts, they are quite on a par. The appearances of nature m which we oblerve actual receflts of th: parts of body from each other, are as diftinct, and as fre

(5.) STEAM, DIFFERENT CAUSES ASSIGNED FOR THE ELASTICITY OF. We know that li quors differ exceedingly in the temperatures neceffary for their ebunition. This forms the great chemical distinction between volatile and fixed bodies. But the difference of temperature in which they boil, or are converted into perma nently elaftic vapour, under the preffure of the atmosphere, is not a certain measure of their differences of volatility. The natural boiling point of a body is that in which it will be converted into elaftic vapour under no preffure, or in vacuo. The boiling point in the open air depends on the law of the elafticity of the vapour in relation to its heat. A fluid A may be lefs volatile, that is, may require, more heat to make it boil in acue, than a fluid B: But if the elafticity of the vapour of A be more increased by an increase of temperature than that of the vapour of B, A may boil at as low, or even at a lower temperature, in the os pen air, than B does; for the increafed elafticity of the vapour of A may fooner overcome the preffure of the atmosphere. Few experiments have been made on the relation between the tempera, ture and the elasticity of different vapours. So long ago as 1765, we had occation to examine the boiling points of all fuch liquors as we could manage in an air-pump; that is, fuch as did not produce vapours which deftroyed the valves and the leathers of the pistons: and we thought that the experiments gave us reafon to conclude, that the elafticity of all the vapours was affected by heat nearly in the fame degree. For we found that the difference between their boiling points in the air and in vacuo was nearly the fame in all, namely, about 120 degrees of Fahrenheit's thermometer. It is exceedingly difficult to make experiments of this kind: The vapours are fo condenfible, and change their elafticity fo prodigiouffy by a trifling change of temperature, that it is almoft impoflible to examine this point with precifion. It is, however, as we shall fee by and by, a fubject of confiderable practical importance in the mechanic arts; and an accurate knowledge of the relation would be of great ufe alfo to the diftiller: and it would be no lefs important to difcover the relation of their elafticity and de: fity, by examining their compreffibility, in the fame manner as we have afcertained the relation in the cafe of what we call aerial fluids, that is, fuch as we have never obferved in the form of liquids or folids, except in confequence of their union with each other or with other bodies. In the article PNEU.

quent

quent and familiar, as the appearances of actual duced, and heat when it is fuddenly condenfed; approach. And if we attempt to go farther in When making experiments with the hopes of dif our contemplation, and to conceive the way and covering the connection between the elafticity and the forces by which either the approximations or dentity of the vapours of boiling water, and alfo receffes of the atoms are produced, we muft ac- of boiling fpirits of turpentine, we found the knowledge that we have no conception of the change of denfity accompanied by a change of matter; and we can only fay, that there is a caufe temperature vaftly greater than in the cafe of inof thete motions, and we call it a force, as in eve- coercible gafes. When the vapour of boiling wa ry cafe of the production of motion. We call it ter was fuddenly allowed to expand into 5 times attraction or repulfion juft as we happen to con- its bulk, we obferved the depreffion of a large and template an accefs or a recefs. But the analogy fenfible air thermometer to be at least 4 or 5 times here is not only flight, but imperfect, and falls greater than in a fimilar expanfion of common air moft in those cafes which are moft fimple, and of the fame temperature. The chemical reader where we should expect it to be most complete. will readily fee reafons for expecting, on the conWe can squeeze water out of a sponge, it is true, trary, a fmalier aiteration of temperature, both or out of a piece of green wood; but when the on account of the much greater rarity of the fluid, white of an egg, the tremella, or fome gums, and on account of a partial condenfation of its fwell to a hundred times their dry dimenfions by water, and the confequent difengagement of com imbibing water, we cannot squeeze out a particle. bined heat. This difference in the quantity of If fluidity (for the reasoning muft equally apply to fire which is combined in vapours and gafes is fo this as to vapourouinefs) be owing to an accu- confiderable as to authorize us to fuppofe that mulation of the extended matter of fire, which there is fome difference in the chemical conftitugradually expanded the folid by its very minute tion of vapours and gafes, and that the connec additions; and if the accumulation round a tion between the specific bafes of the vapour and particle of ice, which is neceflary for making the fire which it contains is not the fame in air, it a particle of water, be fo great in comparison for inftance, as in the vapour of boiling water; of what gives it the expanfion of one degree, and this difference may be the reason why the one as experiment obliges us to conclude-it feems an is easily condenfible by coid, while the other has inevitable confequence that all fluids fhould be never been exhibited in a liquid or folid form, exmany times rarer than the folids from which they cept by means of its chemical union with other were produced. But we know that the difference fubftances. In this particular inftance we know is trifling in all cafes, and in fome (water, for in that there is an effential difference-that in vitai stance, and iron) the folid is rarer than the fluid. or atmospheric air there is not only a prodigious Many other arguments (each of them perhaps of quantity of fire which is not in the vapour of httle weight when taken alone, but which are all water, but that it alfo contains light, or the cause fyftematically connected) concur in rendering it of light, in a combined ftate. This is fully evine much more probable that the matter of fire, in ced by the great difcovery of Mr Cavendish of the caufing elafticity, acts immediately by its own e- compofition of water. Here we are taught that lafticity, which we cannot conceive in any other water (and confequently its vapour) confists of air way than as a mutual tendency in its particles to from which the tight and greateft part of the fire recede from each other; and we doubt not but have been feparated. And the fubfequent difcothat, if it could be obtained alone, we should find veries of the celebrated Lavoifier how, that alit an elaftic fluid like air. We even think that most all the condenfibie gafes with which we are there are cafes in which it is obferved in this ftate. acquainted confift either of airs which have alrea The elaftic force of gunpowder is very much be- dy loft much of their fire (and perhaps light tool, yond the eiafticity of all the vapours which are or of matters in which we have no evidence of fire produced in its deflagration, each of them being or light being combined in this manner. This expanded as much as we can reasonably fuppofe confideration may go far in explaining this differby the great heat to which they are expofed. The ence in the condenfibility of thefe different species writer of this article exploded fome gunpowder of aerial fluids, the gafes and the vapours; and it mixed with a confiderable portion of finely pow is with this qualification only that we are difpofed dered quartz, and another parcel mixed with fine to allow that all bodies are condenfible into liquids filings of copper. The elasticity was meatured by or folids by abftracting the heat. In order that vital the penetration of the ball which was difcharged, air may become liquid or folid, we hold that it is and was great in the degree now mentioned. The not fufficient that a body be prefented to it which experiment was fo conducted, that much of the fhail fimply abftract its heat. This would only abquartz and copper was collected; and none of the ftract its uncombined fire. But another, and much quartz had been meited, and fome of the copper larger portion remains chemically combined by was not melted. The heat, therefore, could not means of light. A chemical affinity must be brought be fuch as to explain the elasticity by expanfion into action which may abstract, not the fire from of the vapours; and it became not improbable the oxygen, (to fpeak in the language of Mr Lathat fire was acting here as a detached chemical voifier,) but the oxygen from the fire and light. fluid by its own elafticity. But to return to our And our production is not the detached bafis of fubject. There is one circumftance in which e air, but detached heat and light, and the formathink our own experiments fhow a remarkabletion of an oxyd of fome kind. To profeente the difference (at ieaft in degree) between the condenfible and incondenfibie vapours. It is well known. that when air is fuddenly expanded, cold is pro

chemical confideration of STEAMS farther than thefe general obfervations, which are applicabie to all, would be almost to wine a treatife of che

mistry,

fhiftry, and would be a repetition of many things words are as follow: "This admirable method which have been treated of in fufficient detail in which I propose of raifing water by the force of other articles of this work. We fhall therefore fire has no bounds if the veffels be ftrong enough; refer the reader to thefe articles; particularly AF- for I have taken a cannon, and having filled it 4ths FINITY, AIR, CHEMISTRY, EVAPORATION, FIRE, fuli of water, and shut up its muzzle and touch, FLAME, HEAT, HYDROGEN, LIGHT, OXYGEN, hole, and expofed it to the fire for 24 hours, it &c. burft with a great explosion. Having afterwards difcovered a method of fortifying veffels internally, and combined them in fuch a way that they filled and acted alternately, I have made the water spout in an uninterrupted stream 40 feet high; one vellel of rarefied water raised 40 of cold water. The person who conducted the operation had nothing to do but turn two cocks; fo that one vessel of water being confumed, another begins to force, and then to fili itfelf with cold water, and fo on in fucceffion."

*To STEAM. V. n. [ fteman, Sax.] 1. To fmoke or vapour with moift heat.—

Let the crude humours dance
In heated brass, fteaming with fire intenfe.

2. To fend up vapours.—

Philips.

Ye mifts that rife from steaming lake. Milton.
See, fee, my brother's ghoft hangs hovering
there,

O'er his warm blood, that steams into the air.
Dryden.
Nay, added fat pollutions of our own,
T' increase the steaming ordures of the stage.
Dryden.

3. To país in vapours.—

The laft deadly smoke aloft did steam. Spenf. -The diffolved amber plainly swam like a thin film upon the liquor, whence it steamed away into the air. Boyle.-These minerais not only iffue out at thefe larger exits, but steam forth through the pores of the earth. Woodward.

(1.) STEAM-ENGINE, n. f. [fteam and engine.] a machine which derives its moving power from the elafticity and condenfibility of the fteam of boiling water. It is the most valuable prefent which the arts of life have ever received from the philofopher. The mariner's compafs, the telescope, gunpowder, and other most useful fervants to human weaknefs and ingenuity, were the productions of chance, and we do not exactly know to whom we are indebted for them; but the fteamengine was, in the very beginning, the refult of reflection, and the production of a very ingenious mind; and every improvement it has received, and every alteration in its construction and principies, were allo the refults of philofophical Rudy.

(2.)STEAM-ENGINE, FIRST INVENTION OF THE. The fteam-engine was beyond all doubt invented by the Marquis of WORCESTER during the reign of Charles II. This nobleman published in 1663 a fmali book intitled A CENTURY OF INVENTIONS; giving fome obfcure and enigmatical account of 100 difcoveries or contrivances of his own, which he extols as of great importance to the public. He appears to have been a person of much know. ledge and great ingenuity: but his defcription or accounts of these inventions seem not so much intended to inftruct the public, as to raise wonder; and his encomiums on their utility and importance are to a great degree extravagant, refembling more the puff of an advertising tradesman than the patriotic communications of a gentleman. The mar quis of Worcester was indeed a projector, and very importunate and myfterious withal in his applications for public encouragement. His ac count, however, of the fteam engine, although by no means fit to give us any diftinct notions of its ftructure and operation, is exact as far as it goes, agreeing precifely with what we now know of the fubject. It is N° 68 of his inventions. His

(3.)STEAM-ENGINE, GRADUAL IMPROVEMENTS OF THE, BY SAVARY AND OTHERS. It does not appear that the noble inventor had interested the public by thefe accounts. His character as a projector, and the many failures which perfons of this turn of mind experienced, probably prejudiced people against him, and prevented ali attention to his projects. It was not till towards the end of the 17th century, when experimental philofophy was profecuted all over Europe with uncommon ardour, that these notions again engaged attention. Capt. Savary, a perfon alfo of great ingenuity and ardent mind, faw the reality and practicability of the marquis of Worcester's project. He knew the great expanfive power of fteam, and had discovered the inconceivable rapidity with which it is reconverted into water by cold; and he foon contrived a machine for raifing water, in which both of these properties were employed. He fays, that it was entirely his own invention. Dr Defagui'iers infifts, that he only copied the marquis's invention, and charges him with grofs plagiarism, and with having bought up and burned the copies of the marquis's book, to fecure the honour of the discovery to himself. This is a very grievous charge, and fhould have been fubftantiated by very diftin&t evidence. Defaguiliers produces none fuch; and he was much too late to know what happened at that time. The argument which he gives is a very foolish one, and gave him no title to confider Savary's experiment as a falfehood; for it might have happened precifely as Savary relates, and not as it happened to Defaguiliers. The fact is, that Savary obtained his patent of invention after a hearing of objections, among which the discovery of the Marquis of Worcester was not mentioned; and it is certain that the account given in the Century of Inventions (above quoted) could inftruct no perfon who was not fufficiently acquainted with the properties of steam to be able to invent the machine himself. Captain Savary obtained his pa❤ tent after having actually erected several machines, of which he gave a description in a book intitled THE MINER'S FRIEND, published in 1696, and in another work published in 1699. Much about this time Dr PAPIN, a Frenchman and fellow of the Royal Society, invented a method of diffolving bones and other animal folids in water, by confining them in clofe veffels, which he called DIGESTERS, fo as to acquire a great degree of

heat.

meafure of a moving force; and he confiders them. A knowledge of both is indifpenfably ne every kind of preffure as competent to the pro- ceffary for acquiring any ufeful practical know. duction of such changes.-He contented himself ledge of machines: and it was ignorance of the with the application of this principie to the mo- doctrines of accelerated and retarded motions tion of bodies by the action of gravity, and gave which made the progrefs of practical mechanical the theory of projectiles, which remains to this knowledge fo very flow and imperfect. The meday without change, and only improved by con- chanics, even of the moderns, before Galileo, went fidering the changes which are produced in it by no further than to ftate the proportion of the the refiftance of the air. (See PROJECTILES, Part power and refiftance which would be balanced by I. Sec. III-VI.) Sir ISAAC NEWTON took up the intervention of a given machine, or the prothis fubject nearly as Galileo had left it. For, if portion of the parts of a machine by which two we except the theory of the centrifugal forces known forces may balance each other. This view arifing from rotation, and the theory of pendu- of the matter introduced a principle, which even Jums, pubished by Huygens, hardly any thing Galielo confidered as a mechanical axiom, viz. that had been added to the fcience of motion. New what is gained in force by means of a machine is ton considered the fubject in its utmost extent; exacly compensated by the additional time which it and in his mathematical principles of natural phi- obliges us to employ. This is falfe in every inftance, lofophy he confiders every conceivable variation and not only prevents improvement in the conof moving force, and determines the motion re- ftruction of machines, but leads us into erroneous fulting from its action.-His firft application of maxims of conftruction. The true principles of thefe doctrines was to explain the celeftial mo- dynamics teach us, that there is a certain proportions; and the magnificence of this fubject caufed tion of the machine, dependant on the kind and it to occupy for a while the whole attention of proportion of the power and refiftance, which the mathematicians. But the fame work contain- enables the machine to perforth the greateft pofed propositions equally conducive to the improve- fible work. It is highly proper therefore to keep raent of common mechanics, and to the complete feparate these two ways of confidering machines, understanding of the mechanical actions of bodies, that both may be improved to the utmoft, and Philofophers began to make thefe applications alfo. then to blend them together in every practical They faw that every kind of work which is to be difcuffion. Statics therefore is preparatory to the performed by a machine may be confidered ab- proper ftudy of mechanics; but it does not hence tractedly as a retarding force; that the impulfe of derive all its importance. It is the fole foundation water or wind, which are employed as moving of many ufeful parts of knowledge. This will be powers, act by means of preffures which they beft feen by a brief enumeration. 1. It compreexert on the impelled point of the machine; and hends all the doctrines of the excitement and prothat the machine itself may be confidcred as an pagation of preffure through the parts of folid affemblage of bodies moveable in certain limited bodies, by which the energies of machines are circumftances, with determined directions and produced. A preffure is exerted on the impelled proportions of velocity. From all thefe confider- point of a machine, fuch as the float-boards or ations refulted a general abftract condition of a buckets of a mill-wheel. This excites a preffure body acted on by known powers. And they at the pivots of its axle, which act on the points of found, that after all conditions of equilibrium fupport. This must be understood, both as to diwere fatisfied, there remains a furplus of moving rection and intenfity, that it may be effectual y reforce. They could now ftate the motion which fifted. A preffure is alfo excited at the acting will enfue, the new refiftance which this will ex- tooth of the cog-wheel on the fame axle, by which cite, the additional power which this will abforb; it urges round another wheel, exciting fimilar and they at last determined a new kind of equili- preffures on its pivots and on the acting tooth brium, not thought of by the ancient mechanici- perhaps of a third wheel. Thus a preffure is ulans, between the resistance to the machine perfor- timately excited in the working point of the mamming work and the moving power, which exactly chine, perhaps a wiper, which lifts a heavy stambalance cach other, and is indicated, not by the per, to let it fall again on fome matter to be reft, but by the uniform motion of the machine.- pounded. Now ftatics teaches us the intensities In like manner, the mathematician was enabled to and direction of all thofe preffures, and therefore calculate that precife motion of water which how much remains at the working point of the would completely abforb, or, in the new language, machine unbalanced by refiftance. 2. It comprebalance the fuperiority of preffure by which wa- hends every circumftance which influences the ftater is forced through a fluice, a pipe, or canal, bility of heavy bodies; the inveftigation and prowith a conftant velocity. Thus the general doc-perties of the centre of gravity; the theory of the frines of motion came to be confidered in two points of view, according as they balanced each other in a state of reft or of uniform motion. Thefe two ways of confidering the fame fubject required both different principles and a different manner of reafoning. The firft has been named STATICS, as expreffing that reft which is the teft of this kind of equilibrium. The fecond has been called DYNAMICS or UNIVERSAL MECHANICS, because the different kinds of motion are characteriftic of the powers or forces which produce

conftruction of arches, vaults, and domes; the attitudes of animals. 3. The ftrength of materials, and the principles of conftruction, fo as to make the proper adjustment of ftrength and ftrain in every part of a machine, edifice, or ftructure of any kind. Statics therefore furnishes us with what may be called a theory of carpentry, and gives us proper inftructions for framing floors, roofs, centres, &c. 4. Statics comprehends the whole doctrine of the preffure of fluids, whether liquid or aeriform, whether arifing from their weight or

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