Page:Cyclopaedia, Chambers - Volume 1.djvu/444

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Ideas; as, poffibly, a Dog does the Shape, Smell, and Voice of his Mailer : yet thefe are rather fo many diftincl Marks whereby he knows him, than one Complex Idea, made out of thole Simple ones.

Composition, in Grammar, the joining of two Words together ; or prefixing a Particle to another Word, to aug- ment, diminifh, or change its Signification.

Composition, in Oratory, the proper Order of the Parts of a Difcourfe, adhering to each other.

To Compofition belongs both the artful joining of the Let- ters whereof the Style is form'd, and whereby it is rendcr'd foft and fmooth, gentle and flowing, or full and fonorous ; or the contrary. See Style.

And the Order, which requires the Grave to be placed after the Humble, and Things firft in Nature and Dignity, before thofe of inferior Confideration. See Period.

Composition, in Painting, includes the Invention and Dii'pofhion of the Figures, the Choice of Attitudes, fS'e. Com* pofition, therefore, confifls of two Parts ; one of which finds out, by means of Hittory, proper Objefts for a Piilure ; and the other difpofes 'cm to advantage. See Painting.

Composition, in Mufick, the Art of difpofing mufical Sounds into Airs, Songs, iSc. either in one, or more Parts ; to be fung with the Voice, or play'd on Inflmments. See Musick, and Song.

Zarlln defines it the Art of joining and combining Con- cords together, which are the Matter of Mufick : But this Definition is too fcanty ; in regard, Difcords are always ufed with Concords in the Compofition of Parts. See Con cord, and Discord.

Under Compofition are comprehended the Rules, firft, of Melody, or the Art of making a fingle Part ; i.e. of contri- ving and difpofing the fimple Sounds, fo as that their Suc- ccflion and Progrcfs may be agreeable. See Melody.

idly, Of Harmony, or the Art of difpofing and concert- ing fevcral fingle Parts fo together, that they may make one agreeable Whole. See Harmony.

It may be here obferv'd, that Melody being chiefly the Bufinefs of the Imagination, the Rules of its Compofition ferve only to prefcribe certain Limits to it ; beyond which, the Imagination, in fearching out the Variety and Beauty of Airs, ought not to go : But Harmony, being the Work of Judgment, its Rules are more certain, exteniive, and more difficult in practice.

In the Variety and Elegancy of the Melody, the Inven- tion labours a great deal more than the Judgment ; fo that Method has but little place : but in Harmony 'tis other- wife ; the Invention, here, has nothing to do ; and the Cora- pofition is conducted from a nice Obfervation of the Rules of Harmony, without any Affiftance from the Imagination at all.

Composition, in Logic, is a Method of reafoning, where- in we proceed from fome general felf-evident Truth, to par- ticular and lingular ones. See Method.

The Method of Compofition, call'd alfo Syntbefit, is juft the reverfe of that of Refolution, or Analyfis. See Reso- lution.

Refoiution is the Method whereby we ordinarily fearch after Truth ; Compofition, that whereby a Truth found, is difcover'd and demonftrated to others: Refolution is the Me- thod of Inveitigation ; Compofition of Demonstration.

The Method of Compofition is that ufed by Euclid, and other Geometricians ; Refolution that ufed by Algebraifts and Philoibphers. The two Methods differ, juil as the Me- thods of fearching a Genealogy; which areeithetby defcend- from the Anceftors to the Poiterity, or by afcending from the Poiterity to their Anceftors ; each have this in common, that their Progreffion is from a thing known, to another un- known.

The Method of Compofition is belt obferv'd by the Mathe- maticians : The Rules hereof are, lit, to offer nothing but what is couch'd in clear exprefs Terms ; and to that End, to begin with Definition, idly, To build only on evident and clear Principles ; to that End, to proceed from Axioms or Maxims-, gdly, To prove demonftratively all the Conclu- iions they draw hence ; and to this purpofe, to make ufc of no Arguments or Proofs, but Definitions already laid down, Axioms alteady granted, and Propoiitions already proved ; which ferve as Principles to Things that follow.

Composition of Motion, is an Aflemblage of fevcral Di- rections of Motion, refulting from Powers acting in different, tho not oppofite Lines. See Motion.

If a Point move or flow according to one and the fame Di- rection ; whether that Motion be equable or not, yet it will {till keep the fame right Line ; the Celerity alone being chang'd, i. e. increas'd, or diminifh'd according to the For- ces with which it is impell'd.

If the Directions be oppofite, as one, e.g. direclly down- ward, the other upward, &c. yet itill the Line of Motion will be the fame.

But if the compounding Motions be not according to the fame Line of Direction, the compound Motion will not be

according to the Line of Direction of either of 'em 1 different one from them both; and this either iir ^ * crooked, according as the Directions or Celerities mall aU - or

If two compounding Motions be each of them equaW the Line of the compound Motion will Hill be a ftrait r.' and this, tho the Motions be neither at right Angles on^ ' another, nor equally fwifr, nor (each to its felf) equabl™ provided that they be but ftmilar ; that is, both accelera^ I and retarded alike. ■

Thus, if the Point a, (Tab. Mechanics, Fig. 4.) De ■ pell'd equally with two Forces ; viz. upwards towards"!" and forwards towards d ; 'Tis plain, that when it i s „ ' forwards as far asrtf, it muft ot m*.-^.-» k..

neceffity be gone upw b rd as far as e e ; lo that were the Motions both equable, it uou i 1 always go on in the Diagonal a e c.

Nay, fuppofe the Motions unequal as to Celerity, f „ as that it move twice as fail upwards as forwards, tf c '.:.' flill it muft go on in the Diagonal a c ; becaufe the Triangle, aee, aec, &c. and acd will ilill be iimilar, being as 'the Motions are.

But, if the Motions be diffimilar, then the compound Motion muft be a Curve. See Circular Motion.

Thus, if a Body, as b, (Fig. 5.) be impell'd or drawn by three different Forces, in the three different Directions hi be, vxmWid, fo that it yields to none of them, but conii' nucs in JEqiullbrio : then will thofe three Powers or Forces be to one another, as three right Lines drawn parallel to thofe Lines, exprefling the three different Directions, and terminated by their mutual Concourfes.

Let b e reprcfent the Force by which the Body b is im- pell'd from b to a, then will the fame right Line be, re- prefent alfo the contrary equal Force, by which it is impell'd from b to e ; but by what hath been faid before, the Force V e is refolvable into the two Forces acting according to the two Directions bd and b c, to which the other impelling from b to e, is as b e to b d, and b c or d e, refpectively.

So iikewife two Forces, acting without the Directions b d, b c, and being equipollent to the Force ailing without the Direction be, from b to e ; will be to the Force ailing ac- cording to the Direction be, from b to e, as bd,bc, to hi: and therefore, the Forces acling in the Directions b d, be, and equipollent to the Force acling in the Directions be, ate to the Force acling in the Direction, as b d, b c, or d c to be: That is, if a Body be urg'd by three different equipollent Powers in the Directions b a, b d, and b c ; thefe three For- ces fhall be to one another as b e, b d, and d e, refpeclivclv.

£e. 2).

T'his Theorem, with its Corollaries, Dr. Keil obferves, it the Foundation of all the new Mechanicks of M. Varlgnmi By help hereof, may the Force of the Mufdes be computed, and moil of the mechanick Theorems in fioreili, de Mem Animalutm, be immediately deduced.

Composition of 'Proportion, fignifies the comparing of the Sums of the Antecedent and Confequent, with the Confequent in two equal Ratios. See Ratio ; fee alfo Com- pound Ratio.

Suppofe 4 : 8 : : 3 : 6 ; by Compofition of Proportion we fay, is is to 8 : as 9 to 6.

There is, however, a great difference between Compofition of Proportion by Addition, and by Multiplication : the In- stance above is of Compofition by Addition. If it had been 4 x 8, it would have been Compofition by Multiplication.

In a word, Compofition of Proportion by Addition, is by Addition of the Indices of the Ratios ; but by Multiplica- tion, it is when the Ratios are multiplied into one another.

Composition, in Pharmacy, the Art, or Act of mixing many Ingredients together into a Medicine ; fo as they may affift each other's Virtues, fupply each others Defects, ot correct any ill Qualities thereof. See Pharmacy.

Composition, in Printing, ordinarily call'd Compofiag, is the arranging of feveral Types, or Letters in the Compofing- Stick, in order to form a Line ; and of feveral Lines rang'il in order in the Galley, to make a Page ; and of feveral of thole to make a Form. See Printing, Page, Form, ifc.

1'he Compofing-Stick is made of Iron generally, fometimes Brafs, or Wood ; of more or lefs length and depth, accord- ing to the Page to be compos'd, or the Compoler's Fancy : It hath two Aiding Pieces, to be faften'd by means of a Nat and Screw, which are flipp'd forwards or backwards, at ths Pleafure of the Compofitor, and according to the Space which the Lines, Notes, iSc. are to take up.

The Compofing-Stick ordinarily contains feven or eight Lines of a middle-fiz'd Letter; which, when fet, are taken out, by help of a thin flip, of Brafs, term'd a Rule, and dif- pos'd in the Galley ; and others compos'd, till a Page bs form'd. The Page being compos'd, is ty'd up, and fet by; and the reft of the Pages of the Sheet p'repar'd in the fame manner : When done, they are carry'd to the Impofing or Corredling-Srone ; there rang'd in order, and difpos'd in a Chafe, or Iron Frame, fitted with wooden Furniture ; then, the Quoins being ftruck in, 'tis carried to the Prcfs to be printed. Sec Press, Case, Chase, £jV.

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