in Natural Philosophy, a general term used to denote the cause by which bodies tend towards each other, and cohere till separated by some other power.
The principle of attraction, in the Newtonian sense of it, seems to have been first furnished by Copernicus, "As for gravity," says Copernicus, "I consider it as nothing more than a certain natural appetence (appetitio) 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 credible that the same power is also inherent in the sun and moon, and planets, that those bodies may constantly retain that round figure in which we behold them." De Rev. Orb. Caelst. lib. i. cap. 9. And Kepler calls gravity a corporeal and mutual affection between similar bodies, in order to their union. Ad Nov. in Introd. And he pronounces more positively, that no bodies whatsoever were absolutely light, but only relatively so; and consequently, that all matter was subjected to the 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, Nov. Organ. lib. ii. aphor. 36. 45. 48. Sylv. cent. i. exp. 33. In France it was received by Fermat and Roberval; and in Italy by Galileo and Borelli. But till Sir Isaac 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 supposed a kind of quality, inherent in certain bodies themselves, and arising from their particular or specific forms. The Newtonian attraction is a more indefinite principle; denoting not any particular kind or manner of action, nor the physical cause of such action; but only a tendency in the general, 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, in his Philosoph. Nat. Prin. Math. notes, "that he uses the words attraction, impulse, and propensity to the centre, indifferently; and cautions the reader not to imagine that Attraction, by attraction he expresses the modus of the action, or the efficient cause thereof, as if there were any proper powers in the centres, which in reality are only mathematical points; or as if centres could attract." Lib. i. p. 5. So he "considers centripetal powers as attractions, though, physically speaking, it were perhaps more just to call them impulses," Ib. p. 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 we have set these aside, there will remain innumerable phenomena of nature, and particularly the gravity or weight of bodies, or their tendency to a centre, which 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 must arise from some cause that penetrates or pervades the whole substance thereof. This unknown principle, unknown we mean in respect of its cause, for its phenomena and effects are most obvious, with all the species and modifications thereof, we call attraction; which is a general name, under which all mutual tendencies, where no physical impulse appears, and which cannot therefore be accounted for from any known laws of nature, may be ranged.
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 see any physical causes thereof; but that, as to our senses, they may really arise from some power or efficacy in such bodies, whereby 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. Such are the attraction of gravity, found in all bodies; and the attraction of magnetism and electricity, found 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 in 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. always proportionably to the quantities of matter, and as the squares of the distances reciprocally) does also obtain in the moon, and the other planets primary and secondary, as well as in the comets; and even that this is the very power whereby 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 settled rules of philosophy, that it obtains in all others: and as it is found to be as the quantity of matter in each body, it must be in every particle thereof; and hence every particle Attraction, in nature is proved to attract every other particle, &c. See ATTRACTION, ASTRONOMY Index.
From this attraction arises all the motion, and consequently all the mutation, in the material world. By this heavy bodies descend, and light ones ascend; by this projectiles are directed, vapours and exhalations rise, and rains, &c. fall. By this rivers glide, the air prelifes, the ocean swells, &c. In effect, the motions arising from this principle make the subject of that extensive branch of mathematics, called mechanics or statics, with the parts or appendages thereof, hydrostatics, pneumatics, &c.
2. That which does not extend to sensible distances. Such is found to obtain in the minute particles whereof bodies are composed, which attract each other at or extremely near the point of contact, with a force much superior to that of gravity, but which at any distance from it decreases much faster than the power of gravity. This power a late ingenious author chooseth to call the attraction of cohesion, as being that whereby the atoms or inensible particles of bodies are united into sensible masses.
This latter 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 to those more remote intelline motions of the component particles of the same bodies, whereon the changes of the texture, colour, properties, &c. of bodies depend: so that our philosophy, if it were only founded on the principle of gravitation, and carried so far as that would lead us, would necessarily be very deficient.
But beside the common laws of sensible masses, the minute parts they are composed of are found subject to some others, which have been but lately taken notice of, and are even yet imperfectly known. Sir Isaac Newton, to whose happy penetration we owe the hint, contents himself to establish that there are such motions in the minima nature, and that they flow from certain powers or forces, not reducible to any of those in the great world. In virtue of these powers, he shows, "That the small particles act on one another even at a distance; and that many of the phenomena of nature are the result thereof. 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, e.g. of salts and water, sulphuric acid and water, nitric acid and iron, sulphuric acid and nitre. He also shows, that these powers, &c. are unequally strong between diffe- Attraction, rent bodies; stronger, e.g. between the particles of potash and those of nitric acid than those of silver, between nitric acid and zinc than iron, between iron and copper than silver or mercury. So sulphuric acid acts on water, but more on iron or copper, &c.
The other experiments which countenance the existence of such principle of attraction in the particles of matter are innumerable.
These actions, in virtue whereof the particles of the bodies above mentioned tend towards each other, the author calls by a general indefinite name attraction; which is equally applicable to all actions whereby distant 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 the particles thereof. Without such principles, there never would have been any motion in the world; and without the continuance thereof, motion would soon perish, there being otherwise a great decrease or diminution thereof, which is only supplied by these active principles.
We need not say 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 certain, philosophy allows of no action but what is by immediate contact and impulsion (for how can a body exert any active power there where it does not exist? to suppose this of any thing, even the Supreme Being himself, would perhaps imply a contradiction): yet we see effects without seeing any such impulse; and where there are effects, we can easily infer there are causes, whether we see them or not. But a man may consider such effects without entering into the consideration 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, will be to leave a great chasm in the history of nature; and to argue about actions which we do not see, will be to build castles in the air.—It follows, therefore, that the phenomena of attraction are matter of physical consideration, and as such entitled to a share in the system of physics; but that the causes thereof will only become so when they become sensible, i.e. when they appear to be the effect of some other higher cause (for a cause is no otherwise seen than as itself is an effect, so that the first cause must from the nature of things be invisible): we are therefore at liberty to suppose the causes of attraction what we please, without any injury to the effects.—The illustrious author himself seems a little irresolve as to the causes; inclining sometimes to attribute gravity to the action of an immaterial cause (Optics, p. 343, &c.) and sometimes to that of a material one (Ib. p. 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, i.e. how motion is communicated by 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 greatest part of common mechanics.
The other species of attraction, therefore, in which no impulse is remarkable, 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, which our conceptions may not be proportionate to: let their causes be occult, as all causes strictly speaking are, so that their effects, which alone immediately concern us, be but apparent.
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 infinitely greater extent than all the mechanics yet known. It is hence alone 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 Keill particularly has endeavoured to deduce some of the laws of this new action, and applied them to solve divers of the more general phenomena of bodies, as cohesion, fluidity, elasticity, softness, fermentation, coagulation, &c.; and Dr Freind, seconding him, has made a further application of the same principles, to account at once 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 attractive force.
But this seems a little too precipitate: A principle so fertile should have been further explored; 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 more of its properties are ascertained, it were better to apply it less and study it more. It may be added, that some of Sir Isaac 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.
Attraction of Mountains. See Mountains. Effective Attraction. See Chemistry Index. Attrebatii. See Attrebatii. Attribute, in a general sense, that which agrees with some person or thing; or a quality determining something to be after a certain manner. Thus understanding is an attribute of mind, and extension an attribute of body. That attribute which the mind conceives Attribute conceives as the foundation of all the rest, is called its essential attribute; thus extension is by some, and solidity by others, esteemed the essential attribute of body or matter.