302 PHYSICS.

SITY AND SR A1UTY. 8. H^KDN'ESS AND SOFTNESS. 9. It K. T-DITY AND FLEXIBILITY'. 10. CONSISTENCE AND FLUIDITY.

3 1. Heat and Cold. id. IIumidity and Siccity. 13.Elasticity'. 14. Odours and Sapours. See Uiese articles.

Inertia is that property of bodies by which they are incapableof any action, so that they cannot put themselves in motion, nordestroy or in anywise alter in themselves (he motion communicat-ed to them by any force, bee Inertia .

Extension of Matter, is the quantity of bulk, or size, determin-ed by their extension in length, breadth, and thickness, or depth ;and these are the common terms, or bounds, which limit the sub-stance of fill bodies.

The divisibility of matter is that universal property or disposi-tion of a body, whereby it is capable of being divided or reducedinto parts, either actually or mentally. See the article Divisibi-lity.

Solidity is that property, whereby a body resists all . othersthat press it on every side, and whereby it hinders all other bodiesfrom entering into that place which it possesses, though they areforced against it ever so violently. 'I'his is sometimes called im-penetrability ; that is, the properly whereby two bodies cannotpenetrate each other, or be in the same place at once. Somehave compounded these two terms, amt called this property ofmutter impenetrable solidity ; and which docs certainly better ex-press it than either of the words singly. This is a property ofmatter so universal that it holds just the same in liquid or fluidbodies, as it is in hard or fixed ones. Thus a drip of water, or aparticle of air, remaining fixed between any two bodies, will noless hinder their contact, than an equal quantity of steel or dia-mond would do.

Eigurabilit;/ of body or matter arises from its extension bywhich it is necessitated to appear in, or put on some sort ol shapeor figure, or other.

Mobility is that essential property of matter by which any partof it is capable of motion, or of a continual and successive changeof place. Motion may be considered, 1. As absolutely tree, orat least so far as to be affected with nothing blit the resistance ofthe medium through which the moving body [Hisses. 2. As de-terminate and under restraint, when the moving body is obligedto move upon or about a fixed point, which is called the centreof motion. The general affections of motion are these three, viz.1.'The celerity or velocity of motion. 2, The quantity of mo-tion. 3. The direction of motion. See Motion, and M kchanics.

'File other properties of bodies noticed above are called specific,because thereby the several kinds of bodies have their divisioninto various species, and are what they are, being thus differencedfrom one another: thus, fire by heat, glass by transparency,liquors by fluidity, solids by their fixity, Ac. are different fromeach other ; and are accounted particular species of matter. Theyare aiso called accidental, because they are not essential to mat-ter, but happen to part tliereoi per accidens, or by accident; forit is purely so, ilia' one part of matter is disposed to be hot, ano-ther cold, another dry, another light, another of this colour, andanother of th.,t. Having referred to the different articles deno-minated specific or accidental properties, we shall here only noticethe peculiar properties of matter called attraction and repulsion.That bodies in some eases approach, and in other cases recede,from each other, without any visible agency is exceedingly ob-vious to all ; the former of these pliamomena is called attraction,the latter repulsion. Teat there are both attraction and repulsionin the material world, according to this sense of the terms, admitsof no dispute ; but whether this is produced by the action of mat-ter upon matter, or by an immaterial force, is nut settled by philosophers. We conceive that an immaterial force is absolutelyrequisite to produce these clDct.-, nor can w ■ conceive of motionat all in matter allowed L. be inert without allowing at the sametime that a force distinct from matter has heen somehow or otheremployed either mediately or immediately to produce that mo-tion. And we can see no di/Yi ulty in admitting thr.t a certain[lower quite different from matter is extended from the surfaces ofthe elementary parts of matter to a certain distance from Unstsurfaces, and that either from stile different circum .tanees of distance this power produces the pliamomena of both attraction and Irepulsion, or that different .arts of matter have separately the dii- !fcre'iit powers applied to them. This being supposed in the first I

instance we may easily account for many cases of attraction andrepulsion occasioned by the action of some fluid, fur this fluid,being first excited or put in motion by these powers, will aifeetthe bodies found in the current, and produce in (hem apparent at-traction or repulsion. The elasticity of bodies, whether solid orfluid, may be accounted for on the principles of attraction and re-pulsion as here explained, and unless these powers be admitted asexisting, and of a different nature from matter we are not able tounderstand any thing at all about the elasticity of bodies ; butthese being admitted, the subject hardly requires explanation.

Attraction is, by the modern philosophers, considered twofold,viz, 1. Attraction of gravitation, whereby one body affects anotherat a. distance, and causes it to gravitate .towards itself. 2. Attrac-tion of cohesion, which we tind only among the very small parti-cles of matter in bodies, and of w hich the chief properties are, 1.This force is then greatest when the particles are in contact, ortouch each other. 2. In homogeneous particles, the greater tinssurface of contact, the s'ronger the force. 3. 'Hie sphere of thisattraction is inconsiderable at any sensible distance from the parti-cle. 4. The smaller the distance, the stronger the force, which isvery great at very small distances. 5. '1 his force decreases neatlyas the cubes of the distances increase ; and not as the squaresthereof, as in the other sort of attraction, ti. This force is pro-portional to the quantity of matter in particles. 7. Consequentlythe densest particle, whose surface ot contact is largest, has thegreatest attraction of cohesion. 8. In particles of the same kind,or equal density, the attraction is stronger between small particlesthan the large ; because in those there is a greater quantity of sur-face than in these, especially if they are of a spherical form.

From this properly of matter proceeds many wonderful andcurious phantomena, which arc easily accountable for on this prin-ciple. As, I. The strong cohesion ot the particles which composesolid or Hard bodies; for without this power, the hardest adamantwould instantly dissolve into an impalpable powder. 2. The pro-digious cohesion of polished surface-', as of glass, stones, metals,&e. Tims two leaden balls pared with a sharp knife, so as to cutoff a segment about one-fourth of an inch diameter, if they arepressed together (giving them a little twist) pretty hard, (hey wilt"require the weight sometimes of 100 pounds to separate them.That this is not owing to the air is plain, because thev are not se-parated in tin: exhausted receiver. 3. My this power," liquids ariseinto the substance of bread, sugar, spungf', and all very porousbodies. 4. On this account also liquids rise on the sides of con-taining vessels, and about tbe surface of bodies floating therein, toa small height above the common level. f>. Particularly on thisprinciple, we account for the ascent of liquids in capillary tubesof glass to so considerable a height above the surface of the liquorin which they are placed, contrary to the laws of hydraulics ; theheights to winch water will arise in different tubes, are recipro-cally as the diameters of the bores of those tubes, and the quan-tities of water drawn up, are directly as those diameters. See(iravesandc’s and Dr. Decsgulier's Courses; Websler’s Principlesof Nat. Phil, page 17. KowningVComp. System. Harris’s J,ex.Tech, under the word Attraction. 6. P>y this means, tbe waterin a vessel will arise between the two polished glass-plates, beingset therein touching each other on the sides, and open a little onthe other sides ; the figure of the water between the plales is thatof an hyperbola, 7. \Vlien particles of matter of different den-sities, quantities of surface, and consequently, of different attrac-tive powers, are mixed together, they will necessarily attract, agi-tate, ami move, each other in various wise, and with incrediblevelocities in many case; ; from hence will arise lennenlations,ebullitions, excale=cencies, fusions, di .solutions, crvslallizations,and other such like effi els known in chemistry. S." Hut amongtlu* small particles of mailer, there is not only an attractive [lower,but abo a repelling one, whereby they are made to recede andflv from cat'll other ; and this force is called repulsion. <). Me.pul ion begins where altractu n ends, anil increases as the dhprtreof particles decrease, it). Particle-attracted most strongly withinthe sphere of its power, are repelled most forcibly when withoutit. II. From the great degn e ot this repulsive [lower in oil,grease, &c. arises the great difficulty of mixing those bodies withwater, so as to make finer purls touch and stitk together. 12.This power is snail between glass and water; greater between"’ass and quicksilver; strong bt tween quicksilver and copper;

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