OF THE. on this fubject. The limits of our Work will not to make ufe of any experiments, there muk be admit of a detail; but we think it neceffary to employed fome general principle by which we can point out the leading principles, and to give the generalize their refults. They will otherwise be traces of that fyftematic connection by which all only narrations of detached facts. We must have the knowledge already poffeffed of this fubject fome notion of that intermedium, by the intermay be brought together and properly arranged. vention of which an external force applied to one This we shall now attempt in as brief a manner part of a lever, joist, or pillar, ocafions a strain on as we are able. a diftant part. This can be nothing but the cohefion between the parts. It is this connecting force, which is brought into action, or, as we more fhortly express it, excited. This action is modified in every part by the laws of mechanics. It is this action which is what we call the strength of that part, and its effect is the train on the ad. joing parts; and thus it is the fame force differently viewed, that conftitutes both the train and the ftrength. When we confder it in the light of a refiftance to fracture, we call it strength. We call every thing a force which we obferve to be ever accompanied by a change of motion; or more strictly speaking, we infer the prefence and agency of a force wherever we observe the state of things in respect of motion different from what we know to be the refult of the action of all the forces which we know to act on the body. Thus when we obferve a rope to prevent a body from failing, we infer a moving force inherent in the rope with as much confidence as when we obferve it drag the body along the ground. The imme, diate action of this force is undoubtedly exerted between the immediately adjoining parts of the rope. The immediate effect is the keeping the. particles of the rope together. They ought to feparate by any external force drawing the ends of the rope contrarywife; and we afcribe their not doing fo to a mechanical force really oppofing this external force. When defired to give it a name, we name it from what we con ceive to be its effect, and therefore its characteriftic, and we call it COHESION. This is merely a name for the fa&t; but it is the same thing in all our denominations. We know nothing of the caufes but in the effects; and our name for the caufe is in fact the name of the effect, which is COHESION. We mean nothing elfe by gravitation or magnetism. What do we mean when we say that Newton understood thoroughly the nature of gravitation, of the force of gravitation; or that Franklin understood the nature of the electric force? Nothing but this: Newton confidered. with patient fagacity the general facts of gravi tation, and has defcribed and claffed them with the utmost precision. In like manner, we shall understand the nature of cohesion when we have discovered with equal generality the laws of cohefion, or general facts which are observed in the appearances, and when we have described and claffed them with equal accuracy. Let us therefore attend to the more fimple and obvious phe nomena of cohefion, and mark with care every circumftance of refemblance by which they may be claffed. Let us receive these as the laws of cohesion characteristic of its fuppofed cause, the force of cohefion. We cannot pretend to enter on this vaft refearch. The modifications are innumerable; and it would require the penetration of more than Newton to detect the circumftance of fimilarity amidst millions of difcriminating cit (4.) STRENGTH OF MATERIALS, PRINCIPLES The frength of materials arifes immediately or ultimately from the cohesion of the parts of bodies. Our examination of this property of tangible matter has as yet been very partial and imperfect, and by no means enables us to apply mathematical calculations with precision and fuccefs. The various modifications of cohefon, in its different appearances of perfect foftnefs, plasticity, ductility, elafticity, haidnefs, have a mighty influence on the ftrength of bodies, but are hardly fofceptible of measurement. Their texture alfo, whether uniform like glafs and ductile metals, cryftallized or granulated like other aetals and freefone, or fibrous like timber, is a circumstance no lefs important; yet even here, although we derive fome advantage from remarking to which of thefe forms of aggregation a fubtance belongs, the aid is but fmall. All we can do in this want of general principles is to make experiments on every clafs of bodies. Accordingly philofophers have endeavoured to inftru&t the public in this particular. The Royal Society of London at its very first inftitution made many experiments at their meetings, as may be feen in the first regifters of the Society. Several individuals have added their experiments. The moft numerous collection in detail is by Mufchenbroek, profeffor of natural philofophy at Leyden. Part of it was published by himself in his Effais de Phyfique, in 2 vols 4to; but the fail collection is to be found in his Syftem of Natural Philofophy, pubhfhed after his death by Luiofs, in 3 vols 4to. This was tranflated from the Low Dutch into French by Sigaud de la Fond, and published at Paris in 1760, and is a prodigious collection of physical knowledge of all kinds, and may almoft fuffice for a 1brary of natural philofophy. But this collection of experiments on the cohesion of bodies is not of that value which one expects. We prefume that they were carefully made and faithfully narrated; but they were made on fuch small specimens that the unavoidable natural inequalities of growth or texture produced irregularities in the refults which bore too great a proportion to the whole quantities obferved. We may make the fame remark on the experiments of Coupiet, Pitot, De la Hire, Du Hamel, and others of the French academy. In fhort, if we except the experiments of Buffon on the ftrength of timber, made at the public expence on a large fcale, there is nothing to be met with from which we can obtain abfolute meafures which may be employed with confidence; and there is nothing in the English language except a fimple lift by Emerfon, which is merely a fet of affirmations, without any narration of circumRances, to enable us to judge of the validity of his conclufions: but the character of Mr Emerfon, as a man of knowledge and of integrity, gives even to these affertions a confiderable value. But cumftances. cumstances. Yet this is the only way of difcovering which are the primary facts characteristic of the force, and which the mod fications. The ftudy is immenfe, but is by no means defperate; and we entertain great hopes that it will ere long be fuccefsfully profecuted; but, in our particular predicament, we must content ourselves with fe. lecting fuch general laws as feem to give us the moft immediate information of the circumftances that must be attended to by the mechanician in his conftructions, that he may unite ftrength with fimplicity, economy, and energy. 1, Then, it is a matter of fact that all bodies are in a certain degree perfectly elaftic; that is, when their form of bulk is changed by certain moderate compreffrons or diftractions, it requires the continuance of the changing force to continue the body in this new fiate; and when the force is removed, the body recovers its originai form. We limit the afsertion to certain moderate changes: for inftance, take a lead wire one 15th of an inch in diameter and ten feet long; fix one end firmly to the ceiling, and let the wire hang perpendicular; affix to the lower end an index like the hand of a watch; on some stand immediately beiow let there be a circle divided into degrees, with its centre correfponding to the lower point of the wire; now turn this index twice round; and thus twift the wire. When the index is let go, it will turn backward again, by the wire's untwifting itself, and make almost four revolutions before it stops; after which it twifts and untwifes many times, the index going backwards and forwards round the circle, diminishing however its arch of twift each time, till at last it fettles precifely in its original pofition. This may be repeated for ever. Now, in this motion, every part of the wire partakes equally of the twift. The particles are ftretched, require force to keep them in their state of extenfion, and recover completely their original relative pofitions. Thefe are all the characters of what the mechanician calis perfect elasticity. (See ELASTICITY.) This is a quality quite familiar in many cases; as in glass, tempered steel, &c. but was thought incompetent to lead, which is generally confidered as having little or no ela fticity. But we make the affertion in the most general terms, with the limitation to moderate derangement of form. We have made the fame experiment on a thread of pipe-ciay, made by forcing foft clay through the fmall hole of a fyringe by means of a ferew; and we found it more elaftic than the lead wire: for a thread of one 20th of an inch diameter and 7 feet lorg allowed the index to make two turns, and yet completely recovered its firft pofition. 2dly, But if we turn the index of the lead wire four times round, and let it go again, it, untwists again in the fame manner, but it makes little more than four turns back again; and after many ofcillations it finally ftops in a pofition almost two revolutions removed from its original pofition. It has now acquired a new arrangement of parts, and this new arrangement is permanent like the former; and, what is of particular moment, it is perfectly claftic. This change is familiarly known by the denomination of a SET. The wire is faid to have TAKEN A SET. When we attend minutely to the proce dure of nature in this phenomenon, we find that the particles have as it were flid on each other, ftill cohering, and have taken a new pofition, in which their connecting forces are in equilibrio and in this change of relative fituation, it appears the connecting forces which maintained the particles in their firft fituations were not in equibrio in fome pofition intermediate between that of the firft and that of the laft form. The force requir ed for changing this first form augmented with the change, but only to a certain degree; and du ring this procefs the connecting forces always tended to the recovery of this firft form. But af ter the change of mutual pofition has paffed a cer tain magnitude, the union has been partly deftroyed, and the particles have been brought into new fituations; that the forces which now connect each with its neighbour tend, not to the recovery of the first arragement, but to push them farther from it, into a new fituation, to which they now verge, and require force to prevent them from acquiring. The wire is now in fact again perfectly elaftic; that is, the forces which now connect the particles with their new neigh bours augment to a certain degree as the derangement from this new pofition augments. This is reasoning not from any theory. It is narrating facts, on which a theory is to be founded. What we have been juft now faying is evidently a description of that fenfible form of tangible matter which we call ductility. It has every gradation of variety, from the foftness of butter to the firmneis of gold. All thefe bodies have fome elafticity; but we fay they are not perfectly elaftic, because they do not com. pletely recover their original form when it has been greatly deranged. The whole gradation may be moft diftinétly observed in a piece of glass or hard fealing-wax. In the ordinary form glats is per haps the most completely elastic body that we know, and may be bent till juft ready to fnap, and yet completely recovers its first form, and takes no fet whatever; but when heated to such a degree as juft to be visible in the dark, it lofes its brittleness, and becomes so tough that it cannot be broken by any blow; but it is no longer elastic, takes any set, and keeps it. When more heated, it becomes as plaftic as clay; but in this ftate is remarkably diftinguifhed from clay by a quality which we may call VISCIDITY, which is fomething like elasticity, of which clay and other bodies purely plaftic exhibit no appearance. This is the joint operation of strong adhesion and softnefs. When a rod of perfectly foft glafs is fuddenly ftretched a little, it does not at once take the thape which it acquires after a thort time. It is owing to this, that in taking the impreffion of a fea!, if we take off the feal while the wax is yet very hot, the sharpness of the impreffion is de ftroyed immediately. Each part drawing its neighbour, and each part yielding, the prominent parts are pulled down and blunted, and the sharp hollows are puiled upwards and alfo blunted. The feal must be kept on till all has become not only ftiff but hard. This vifcidity is to be obferved in ail plaftic bodies which are homogeneous. It is not obferved in clay, because it is not homogeneous, but confifts of hard particles of the argillaceous earth ticking together by their attraction of feveral particles an almoft impenetrable my tery. We must therefore content ourselves, for a long while to come, with a careful obferva. tion of the fi mpieft cafes that we can propofe, and with the discovery of fecondary laws of action, in which many particles combine their influence. Our readers are requested to accept of thefe endeavours, not fo much to communicate information on this important and difficult subject, as to excite curiofity and farther experiments.Many ufeful deductions might be made from these premises refpecting the manner of difpofing and combining the ftrength of materials in our ftructures. The beft form of joints, mortifes, te nons, fearfs; the rules for juggling, tabling, faying, fishing, &c. practifed in the delicate art of mafl-making, are all founded on this doctrine: but the difcuffion of thefe would be equivalent to writing a complete treatife of carpentry. We hope that this will be executed by fome intelli gent mechanician, for there is nothing in our language on this fubject but what is almost contemptible; yet there is no mechanic art that is more fufceptible of scientific treatment. Such a trea tife, if well executed, could not fail of being well received by the public in this age of mechanical improvement. *To STRENGTH. v. a. To strengthen. Not used. Edward's happy-order'd reign, moft fertile breeds Plenty of mighty spirits, to strength his state. attraction for water. Something like it might be made of finely powdered glas and a clammy fluid fuch as turpentine. Vifcidity has all de grees of foftnefs till it degenerates to ropy fluidity like that of olive oil. When ductility and elafticity are combined in different proportions, an immenfe variety of fentible modes of aggregation may be produced. Some degree of both are probably to be obferved in all bodies of complex conftitution; that is, which confift of particles made up of many different kinds of atoms. Such a conftitution of a body must afford many fituations permanent, but eafily deranged. In all thefe changes of difpofition which take place among the particles of a ductile body, the particles are at fuch diftance that they ftill cohere. The body may be stretched a little; and on removing the extending force, the body fhrinks into its firft form. It also refifts moderate compreffions; and when the compreffing force is removed, the body fwells out again. Now the corpufcuiar fa&t here is, that the particles are acted on by attractions and repulfions, which balance each other when no external force is acting on the body, and which augment as the particles are made, by any external caufe, to recede from this fituation of mutual inactivity; for fince force is requifite to produce either the dilatation or the compreflion, and to maintain it, we are obliged, by the conftitution of our minds, to infer that it is oppofed by a force accompanying or inherent in every particle of dilatable or compreffible matter: and as this neceflity of employing force to produce a change indicates the agency of these corpufcular forces, and marks their kind, according as the tendencies of the particles appear to be toward each other in dilatation, or from each other in compreflion; fo it alfo measures the degrees of their intenfity. Shou d it require three times the force to produce a double compreflion, we must reckon the mutual repulfions triple when the compreffion is doubled; and fo in other inftances. We fee from all this that the phenomena of cohefion indicate fome relation between the intenfity of the force of cobefion and the diftance between the centres of the particles. To discover this relation is the great problem in corpufcular mechanifin, as it was in the Newtonian invefti. gation of the force of gravitation. Could we difcover this law of action between the corpufcles with the fame certainty and diftin&tnefs, we might with equal confidence fay what will be the refult of any pofition which we give to the particles of bodies but this is beyond our hopes. The law of gravitation is fo limple that the difcovery or detection of it amid the variety of celestial phenomena required but one step; and in its own nature its poffible combinations still do not greatly exceed the powers of hun in refearch. One is aimoft difpofed to fay that the Supreme Being has exhibited it to our reafoning powers as fuficient to employ with fucecfs our utmost efforts, but not to abrufe as to difcourage us from the noble attempt. It ieems to be otherwife with respect to cohefion. Mathematics informs us, that it it deviates fenfibly from the law of gravitation, the Ampleft combinations will make the joint action If it were true that women were thus naturally vain and light, then how much more blameable is that education, which feems contrived to flrengthen and creafe their foily. Law. 3. To animate; to fix in refolution.-They firengthened their hands for this work. Neh. ii. 18.-Charge Jofliua, and encourage him and frengthen him. Deut. 4. To make to increase in power or fecurity.— Let noble Varwick, Cobham, and the rest, With powerful policy frengthen themfelves. Shok. They fought the frengthening of the heathen. I Mac. vi. (2.) To STRENGTHEN, v. n. To grow strong. Oh men for flatt'ry and deceit renown'd ! As your years increase, that firengthens too, T'undo poor maids. Otway. The disease that shall destroy at length, Grows with her growth, and lrengthens with his frength. Peje. (1.) STRENGTHENER. STRENGTHNER. . f. [from Brength: by contraction rengthner.] I. That which gives ftrength; that which makes throng.-Garlick is a great #trengthner of the ftomach. Temple. 2. [In mediciae) Strengtheners add the As the wretch, whofe fever-weaken'd joints, Like Atrengthlefs hinges, buckle under life, Impatient of his fit, breaks like a fire Out of his keeper's arms. Shak. 2. Wanting potency; weak. Ufed of liquors This liquor must be inflammable or not, and yet fubtile and pungent, which may be called fpirit; or elfe ftrengthlefs or infipid, which may be named phlegm. Boyle. STRENGTHNER. See STRENGTHENER. STRENIA, in the Roman mythology, the goddefs of Strength. She was fabled to be the daugh ter of Pallas and Styx, and the fifter of VALOUR and VICTORY. *STRENUOUS. adj. [ftrenuus, Lat.] 1. Brave; boid; active; valiant; dangerously laborious.— Nations grown corrupt Love bondage more than liberty; Bondage with ease than ftrenuous liberty. Mili. 2. Zealous; vehement.-He refolves to be ftrenuous for taking off the teft. Swift.-Citizens within the bills of mortality have been Arenuous against the church and crown. Swift. * STRENUOUSLY. adv. [from frenuous,] 1. Vigorously; actively.-Many can use both hands, yet will there divers remain that can frenuously make ufe of neither. Brown. 2. Zealously; vehemently; with ardour.-Writers difpute ftrenuously for the liberty of conscience. Savift.-There was no true Catholick but ftrenuously contended for it. Waterland. STREPEROUS. adj. [ftrepo, Lat.] Loud; noify.-Porta conceives, because in a treperous eruption it rifeth against fire, it doth therefore refift lightning. Brown. STRESS. n. f. [ftece, Saxon, violence; or from diftrefs. 1. Importance; important part.The firefs of the fable lies upon the hazard of having a numerous stock of children. L'Estrange. This, on which the great firefs of the bufinefs depends, would have been made out with reafons fufficient. Locke. 2. Importance imputed; weight afcribed. A body may as well lay too little as too much stress upon a dream. L'Eftrange.-It fhew ed how very little ftrefs is to be laid upon the precedents they bring. Leley.-Confider how great a firefs he laid upon this duty, while upon earth. Atterbury. 3 Violence; force, either acting or fuffered. By stress of weather driv'n, by exercise, yet they must not be put to a stress beyond their ftrength. Locke. To STRESS. v. a. (Evidently from distress} To diftrefs; to put to hardflips or difficulties.Stirred with pity of the ftreffed plight Of this fad realm. Spenfer. * STRETCH. n. f. [from the verb.] 1. Extenfion; reach; occupation of more space. At all her ftretch her little wings the fpread. Dryden. -Difruption, as ftrong as they are, the bones would be in fome danger of, upon a great and fudden Stretch or contortion, if they were dry. Ray. 2. Force of body extended. He thought to fwim the ftormy main, By stretch of arms. Dryden. 3. Effort; ftruggle from the act of running.Thofe put a lawful authority upon the stretch to the abufe of power. L'Eftrange.-Upon this alarm we made incredible stretches towards the South, to gain the faftnefles of Prefton. Addison. 4. Utmost extent of meaning.-Quotations, in their utmoft stretch, can fignify no more than that Luther lay under fevere agonies of mind. Atterbury. 5: Utmoft reach of power. This is the utmost stretch that nature can, And all beyond is fulfome, false, and vain. Granville (1.) * TO STRETCH. v. a. [firecan, Sax. ftreekea, Dutch.] 1. To extend; to fpread out to a diftance. The stretching out of his wings fhall fill the breadth of thy land. If. viii. 8.-Stretch thine hand unto the poor. Ecclus, vii. 32.-Take thy rod, and stretch out thine hand. Ex. vii. 19.Eden Stretch'd her line 2. From Auran, eastward to the royal towers To elongate, or ftrain to a greater spáce.— All thy dominion, Adam is no more 3. To expand; to display. Milton Milton Leviathan on the deep, Stretch'd like a promontory, fleeps. -What more likely to stretch forth the heavens, and lay the foundation of the earth, than infinite power? Tillotson. 4. To ftrain to the utmost.This kifs, if it durft fpeak, Would stretch thy fpirits up into the air. Shak, 5. To make tenfe. So the ftretch'd cord the fhackl'd dancer tries. Smith 6. To carry by violence farther than is right; to ftrain: as, to stretch a text; to stretch credit. (2.) To STRETCH. V. N. 1. To be extended, locally, intellectually, or confequentially.-Idolatry is a horrible fin, yet doth repentance Stretch unto it. Whitgifte What! will the fine stretch out to th' crack of doom? Shakespeare. This to rich Ophir's rifing morn is known, And ftretch out far to the burnt swarthy zone. Cowley Your dungeon stretching far and wide beneath. } Dryden. Milton. At laft they landed. membrane. 1 STR tfelf in the liquor, expofed to the open air, did membrane, that involved the liquors of the egg, STRETCHER. n. f. [from stretch.] 1. Any The Stretcher of Ulyffes' firing And his fteeles piercer. They tug at ev'ry oar, and every Stretcher STRETTO, adv. in Italian mufic, is sometimes ufed to fignify that the measure is to be fhort and concife, and confequently quick. In this fenfe it ftands opposed to LARGO. STREUSDORF, a town of Germany, in Up. per Saxony, in Coburg; 4 miles S. of Hilldburghaufen. * To STREW. v. a. [The orthography of this The fuow which does the top of Pindus ftrew, 2. To spread by scattering.— I thought thy bride-bed to have deck'd, fweet Shak. Milton. And not have ftrew'd thy grave. Some flowers and fome bays, For thy herfe, to strew the ways. 3. To fcatter ioofely.-The calf he burnt in the fire, ground it to powder, and traved it upon the water, and made Ifrael drink of it. Ex. Whom ev'n the favage beafts had fpar'd, they kili'd, * STREWMENT. n. f. [from frew.] thing fcattered in decoration. And Strew'd his mangled limbs about the field. Here fhe is allow'd her virgin chants, * (1.) STRIATE. adj. [from Atria, Lat. ftriæ.-Thefe effluviums fly by ftriated atoms. (1.) * STRIATED. ftrié, Fr.] Formed in have been a fun, and fo the centre of a leffer vorBrown-Des Cartes imagines this earth once to tex, whofe axis ftiil kept the fame pofture, by reafon of the ftriate particles finding no fit pores for Cryftal, when incorporated with the fibrous talcs, their paffages, but only in this direction. Rayfhews, if broken, a ftriated or fibrous texture, like thofe of taics. Woodward. that has a number of longitudinal furrows on its (2.) STRIATED LEAF, among botanists, one furface. riety of Indurated Carbonat of Lime. See MINER(3.) STRIATED LIMESTONE, a fpecies or vaALOGY, Part II. Chap. IV. Class I. Ord. II. Gen. I. Sp. I. § II. Var. 4. Fr.] Difpofition of ftriæ.-Parts of tuberous hæ* STRIATURE. n. f. [from fria; frieure, matitæ fhew feveral varieties in the cruft, Ariature, and texture of the body. Woodward. berdeenshire, in the district of Buchan, compre(1.) STRICHEN, a parish of Scotland, in Ahending about 8000 acres; of an oblong form, floping to the banks of the Ugie, about 13 miles with plantations; and there are some trees about above its mouth. The furface is ornamented the houfe of Strichen, the feat of Mr Frafer, so “ old, that Dr JOHNSON himself acknowledged, The population, in 1792, was 1400; the increase they were of full growth, and worthy of notice." 252, fince 1755. The hills abound with ftones, and one of them has ftones of the fpecies called PETUNTSE, about 15 miles from Peterhead; containing about of bad omen.- The rueful trick, ftill waiting on the bier. Spenf. (2.) STRICK. See STRIX. STRICKATHROW, a parish of Scotland, in frike; but it has in the antiquated phrafe fricken (that |