ATTRACTION

, or Attactive Power, a general term used to denote the cause, power, or principle, by which all bodies mutually tend towards each other, and cohere, till separated by some other power. The laws, phenomena, &c, of attraction, form the chief subject of Newton's philosophy, being the principal agent of nature, in almost all her wonderful operations.

The principle of attraction, in the Newtonian sense of it, it seems was first surmised by Copernicus. “As for gravity, says he, I consider it as nothing more than a certain natural appetence (appetentia) that the Creator has impressed upon all the parts of matter, in order to their uniting or coalescing into a globular form, for their better preservation; and it is probable that the same power is also inherent in the sun and moon, and planets, that those bodies may constantly retain that round form in which we see them.” De Revol. Orb. Cælest. lib. i, cap. 9. Kepler calls gravity a corporeal and mutual affection between similar bodies, in order to their union. Ast. Nov. in Introd. And he pronounced more positively that no bodies whatever were absolutely light, but only relatively so; and consequently that all matter was subjected to the power and law of gravitation. Ibid.

The first in this country who adopted the notion of attraction, was Dr. Gilbert, in his book De Magnete; and the next was the celebrated Lord Bacon, in his Nov. Organ. lib. ii, aphor. 36, 45, 48. Sylv. cent. i, | exp. 33; also in his treatise De Motu, particularly under the articles of the 9th and the 13th sorts of Motion. In France it was received by Fermat and Roberval; and in Italy by Galileo and Borelli. But till Newton appeared, this principle was very imperfectly defined and applied.

It must be observed, that though this great author makes use of the word attraction, in common with the school philosophers, yet he very studiously distinguishes between the ideas. The ancient attraction was conceived to be a kind of quality inherent in certain bodies themselves, and arising from their particular or specific forms. But the Newtonian attraction is a more indefinite principle; denoting not any particular kind or mode of action; nor the physical cause of such action; but only a general tendency, a conatus accedendi, to whatever cause, physical or metaphysical, such effect be owing; whether to a power inherent in the bodies themselves, or to the impulse of an external agent. Accordingly, that author remarks, in his Philos. Nat. Prin. Math. “that he uses the words attraction, impulse, and propension to the centre, indifferently; and cautions the reader not to imagine that by attraction he expresses the modus of the action, or its efficient cause, as if there were any proper powers in the centres, which in reality are only mathematical points; or as if centres could attract.” Lib. 1, pa. 5. So, he “considers centripetal powers as attractions, though, physically speaking, it were perhaps more just to call them impulses. Ib. pa. 147. He adds, “that what he calls attraction may possibly be effected by impulse, though not a common or corporeal impulse, or after some other manner unknown to us.” Optic. p. 322.

Attraction, if considered as a quality arising from the specific forms of bodies, ought, together with sympathy, antipathy, and the whole tribe of occult qualities, to be exploded. But when these are set aside, there will remain innumerable phenomena of nature, and particularly the gravity or weight of bodies, or their tendency to a centre, that argue a principle of action seemingly distinct from impulse; where, at least, there is no sensible impulsion concerned. Nay, what is more, this action, in some respects, differs from all impulsion we know of; impulse being always found to act in proportion to the surfaces of bodies; whereas gravity acts according to their solid content, and consequently it must arise from some cause that penetrates or pervades the whole Tubstance of it. This unknown principle, unknown we mean in respect of its cause, for its phenomena and effects are most obvious, with all its species and modifications, is called attraction; being a general name, under which may be ranged all mutual tendencies, where no physical impulse appears, and which consequently cannot be accounted for upon any known laws of nature.

And hence arise divers particular kinds of attraction; as Gravity, Magnetism, Electricity, &c, which are so many different principles, acting by different laws; and only agreeing in this, that we do not perceive any physical causes of them: but that, as to our senses, they may really arise from some power or efficacy in such bodies, by which they are enabled to act even upon distant bodies; though our reason absolutely disallows of any such action.

Attraction may be divided, with respect to the law it observes, into two kinds.

1. That which extends to a sensible distance. As the attraction of gravity, which is found in all bodies; and the attractions of magnetism and electricity, found only in particular bodies. The several laws and phenomena of each, see under their respective articles.

The attraction of gravity, called also among mathematicians the centripetal force, is one of the greatest and most universal principles of all nature. We see and feel it operate on bodies near the earth, and find by observation that the same power (i. e. a power which acts in the same manner, and by the same rules, viz, aways proportionally to the quantities of matter, and inversely as the squares of the distances) does also obtain in the moon, and the other planets, both primary and secondary, as well as in the comets; and even that this is the very power by which they are all retained in their orbits, &c. And hence, as gravity is found in all the bodies which come under our observation, it is easily inferred, by one of the established rules of philosophizing, that it obtains in all others. And since it is found to be proportional to the quantity of matter in any body, it must exist in every particle of it: and hence it is proved that every particle in nature attracts every other particle.

From this attraction arises all the motion, and consequently all the mutation, in the great world. By this heavy bodies descend, and light ones are made to ascend: by this projectiles are directed, vapours and exhalations rise, and rains &c fall: by this rivers glide, the ocean swells, the air presses, &c. In short, the motions and forces arising from this principle, constitute the subject of that extensive branch of mathematics, called mechanics or statics, with the parts or appendages of it, as hydrostatics, pneumatics, hydraulics, &c.

2. That which does not extend to sensible distances. Such is found to obtain in the minute particles of which bodies are composed, attracting each other at or extremely near the point of contact, with forces often much superior to that of gravity, but which at any distance decrease much faster than the power of gravity. This power a late ingenious author calls the attraction of cohesion, as being that by which the atoms or insensible particles of bodies are united into sensible masses.

This kind of attraction owns Sir Isaac Newton for its discoverer; as the former does for its improver. The laws of motion, percussion, &c, in sensible bodies, under various circumstances, as falling, projected, &c, ascertained by the later philosophers, do not reach those more recluse, intestine motions in the component particles of the same bodies, on which depend the changes in the texture, colour, properties, &c, of bodies. So that our philosophy, if it were only founded on the principle of gravitation, and even carried as far as this would lead us, would still be very deficient.

But besides the common laws of sensible masses, the minute parts they are composed of are found subject to some others, which have but lately been noticed, and are even yet imperfectly known. Newton himself, to whose happy penetration we owe the hint, limits himself with establishing that there are such motions in the | minima naturæ, and that they flow from certain powers or forces, not reducible to any of those in the great world. He shews that, by virtue of these powers, “the small particles act on one another even at a distance; and that many of the phenomena of nature result from it. Sensible bodies, we have already observed, act on one another divers ways; and as we thus perceive the tenor and course of nature, it appears highly probable that there may be other powers of the like kind; nature being very uniform and consistent with herself. Those just mentioned, reach to sensible distances, and so have been observed by vulgar eyes; but there may be others which reach to such small distances as have hitherto escaped observation; and it is probable electricity may reach to such distances, even without being excited by friction.”

The great author just mentioned proceeds to confirm the reality of these suspicions from a great number of phenomena and experiments, which plainly argue such powers and actions between the particles, for example of salts and water, oil of vitriol and water, aquafortis and iron, spirit of vitriol and saltpetre. He also shews, that these powers, &c, are unequally strong between different bodies; stronger, for instance, between the particles of salt of tartar and those of aquafortis than those of silver, between aquafortis and lapis calaminaris than iron, between iron than copper, and copper than silver or mercury. So spirit of vitriol acts on water, but more on iron or copper, &c. And the other experiments are innumerable which countenance the existence of such principle of attraction in the particles of matter.

These actions, by virtue of which the particles of the bodies above-mentioned tend towards each other, the author calls by a general indefinite name, attraction; a name equally applicable to all actions by which bodies tend towards one another, whether by impulse, or by any other more latent power: and from hence he accounts for an infinity of phenomena, otherwise inexplicable, to which the principle of gravity is inadequate.

Thus, adds our author, “will nature be found very conformable to herself, and very simple; performing all the great motions of the heavenly bodies by the attraction of gravity, which intercedes those bodies, and almost all the small ones of their parts, by some other attractive power diffused through their particles. Without such principles, there never would have been any motion in the world; and without the continuance of it, motion would soon perish, there being otherwise a great decrease or diminution of it, which is only supplied by these active principles.”

It need not be said how unjust it is in the generality of foreign philosophers to declare against a principle which furnishes so beautiful a view, for no other reason but because they cannot conceive how one body should act on another at a distance. It is indeed true, that philosophy allows of no action but what is by immediate contact and impulsion; for how can a body exert any active power where it does not exist? yet we see effects, without perceiving any such impulse; and where effects are observed, there must exist causes whether we see them or not. But we may contemplate such effects, without entering into the considera- tion of the causes, as indeed it seems the business of a philosopher to do: for to exclude a number of phenomena which we do see, would be to leave a great chasm in the history of nature; and to argue about actions which we do not see, would be to raise castles in the air. It follows therefore, that the phenomena of attraction are matter of physical consideration, and as such intitled to a share in the system of physics; but that their causes will only become so when they become sensible, that is when they appear to be the effect of some other higher causes; for a cause is no otherwise seen than as itself is an effect, so that the first cause must needs be always invisible: we are therefore at liberty to suppose the causes of attractions what we please, without any injury to the effects. The illustrious author himself seems to be a little indetermined as to the causes; inclining sometimes to attribute gravity to the action of an immaterial cause (Optics, pa. 343 &c), and sometimes to that of a material one, Ib. pa. 325.

In his philosophy, the research into causes is the last thing, and never comes under consideration till the laws and phenomena of the effect be settled; it being to these phenomena that the cause is to be accommodated. The cause even of any, the grossest and most sensible action, is not adequately known. How impulse or percussion itself produces its effects, that is how motion is communicated from body to body, confounds the deepest philosophers; yet is impulse received not only into philosophy, but into mathematics: and accordingly the laws and phenomena of its effects make the chief part of common mechanics.

The other species of attraction, therefore, in which no impulse is observable, when their phenomena are sufficiently ascertained, have the same title to be promoted from physical to mathematical consideration; and this without any previous inquiry into their causes, to which our conceptions may not be proportionate.

Our great philosopher, then, far from adulterating science with any thing foreign or metaphysical, as many have reproached him with doing, has the glory of having thrown every thing of this kind out of his system, and of having opened a new source of sublimer mechanics, which, duly cultivated, might be of far greater extent than all the mechanics yet known. Hence it is alone that we must expect to learn the manner of the changes, productions, generations, corruptions, &c, of natural things; with all that scene of wonders opened to us by the operations of chemistry.

Some of our own countrymen have prosecuted the discovery with laudable zeal. Dr. Keil particularly has endeavoured to deduce some of the laws of this new action, and applied them in resolving several of the more general phenomena of matter, as cohesion, fluidity, elasticity, softness, fermentation, coagulation, &c: and Dr. Freind, seconding his endeavours, has made a farther application of the same principles, at once to account for almost all the phenomena that chemistry presents. So that some philosophers are inclined to think that the new mechanics should seem already raised to a complete science, and that nothing now can occur but what we have an immediate solution of, from the principles of attractive forces. |

But this seems a little too precipitate: a principle so fertile should have been further explained; its particular laws, limits, &c, more industriously detected and laid down, before we had proceeded to the application. Attraction in the gross is so complex a thing, that it may solve a thousand different phenomena alike. The notion is but one degree more simple and precise than action itself; and, till its properties are more fully ascertained, it were better to apply it less, and study it more. It may be added, that some of Newton's followers have been charged with falling into that error which he industriously avoided, viz, of considering attraction as a cause or active property in bodies, not merely as a phenomenon or effect.

For the laws, properties, &c, of the different sorts of Attraction, see their particular articles Cohesion, Gravity, Magnetism, &c.

Attraction

, Centre of, See Centre of Attraction.

Attraction of Mountains, See Mountains.

Attrition

, the striking or rubbing of bodies against one another, so as to throw off some of their superficial particles: such as the grinding and polishing of bodies. Or simply the act of rubbing: as when amber and other electric bodies are rubbed, to make them attract, or emit their electric force.

Avant-Foss, or Ditch of the Counterscarp, in Fortification, is a wet ditch surrounding the counterscarp, on the outer side, next to the country, at the foot of the glacis. It would not be proper to have such a ditch if it could be laid dry, as it would then serve as a lodgment for the enemy.

Averroes

, or Aben-Roes, a very subtile Arabian philosopher, who flourished about the end of the 11th century, when the Moors had possession of part of Spain. He was the son of the high priest and chief judge of Corduba or Cordova in Spain: but he was educated in the university of Morocco, where he was professor, and where he died in 1206, having there studied natural philosophy, medicine, mathematics, law, and divinity. After the death of his father, he enjoyed his posts in Spain, to which was afterward added that of judge of Morocco and Mauritania, where having settled deputies, he returned to his duty in Spain. Notwithstanding he was very rich, and had a very great income, his liberality to men of letters in necessity, whether they were his friends or his enemies, kept him always in debt. He was afterwards stripped of all his posts, and thrown into prison, for heresy, by the instigations of bad men, his enemies; but the oppressions of the judge who succeeded him, caused him to be restored to his former employments.

He was excessively fat, though he eat but once a day, and spent most part of the night in the study of philosophy, when he was fatigued, amusing himself with reading poetry or history. He was never seen to play at any game, or to partake in any diversion. He was extremely fond of Aristotle's works, and wrote commentaries upon them; whence he was styled the Commentator, by way of eminence. He wrote many other pieces; among them a work on the Whole Art of Physic; an Epitome of Ptolomy's Almagest, which Vossius dates about the year 1149; also a Treatise of Astrology, which was translated into Hebrew by R. Jacob Ben Samson, and said to be extant in the French king's library. He wrote also several poems, and many amorous verses, but these last he threw into the fire when he grew old. His other poems are lost, except a small piece, in which he says, “that when he was young, he acted against his reason; but that when he was in years, he sollowed its dictates;” upon which he utters this wish, “Would to God I had been born old, and that in my youth I had been in a state of perfection!” As to religion, his opinions were, that Christianity is absurd; Judaism, the religion of children; Mahometanism, the religion of swine.

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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.

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ASYMPTOTE
ATLANTIDES
ATMOSPHERE
ATOM
ATOMICAL Philosophy
* ATTRACTION
AVICENA
AUGUST
AURIGA
AURORA
AURUM Fulminans