A T T 



that which arifca from the eveftion of the mooi,, cfcaped 

 h,s rdearchc. lie ha. perfeftly efl.bh.hal the principle 

 which he had difcovered ; bi.t left the complete dcvclopc- 

 ment ot its confeqnences and advantages to the "cumc 

 tcrs that (liould fucceeil him. '^ 



The profound analyfis, of which thi,. great man was 

 alfo the inventor had not, at this time, been fufliciently 

 perfefted, to enable him to give complete folulions to all 

 the diliiciilt problems which arife in conlidcring the the 

 ory of the fydem of the world ; fo that he was fome- 

 times obliged to give only imperfeft l1<etches or approxi- 

 mations, and leave them to be verified by a more rigorous 

 calculation. But, notwithllanding tiiefe inevitable dtfeas, 

 the importance and generality of his difcoverie-, and t!ie 

 }{reat number of his original and profound views, whicli 

 have given rife to the moll brilliant mathematical theories 

 of the prefent age, will always affure to this performance 

 the pre-en-.iner.ce above every other fimilar pruduiftion of 

 tlie human mind. 



Having thus given a concife hillory of the difcovery of 

 this extenllve principle, and its application to the laws of 

 motion, it is proper to obferve, that thon^di Newton makes 

 ufe of the word attraction in common with the fchool phi- 

 lofophers, yet he very ftudioudy diftinguilhed between the 

 ideas. The ancient attraction was fuppofed to be a kind 

 of qi-ality, inh^-rent in certain bodies thcmfelves, and arifuKJ- 

 from their particular or fpecific forms ; but the Newtonian 

 attraftion is a more indelinite principle, denoting no par- 

 ticular kind or manner of aftion, nor the phyfical caufcs of 

 fuch adlion, but only tendency in the general, a co.'iafus 

 arccilcndt, to whatever caufe, phyfical or metaphyfical, fuch 

 effefts be owing, whether to a power inherent in the bodies 

 themfelves, or to the impulfe of an external agent. 



He accordingly fhews in his Philoi'oph. Nat. Prin. Math, 

 that he iifes th- words attraftion, impulfe, and propenfion 

 to the centre, indilTerently ; and cautions the reader not to 

 imagine, that by attraction he expreflcs the modus of the 

 action, or the efficient caufe thereof, as if there were any 

 proper powers in the centres, which in reality are only ma- 

 thematical points; or as if centres could attraft. Lib. i. p. 5. 

 In hke manner he confiders centripetal powers as attractions, 

 though phyfically fpcaking, it were more jnll to call them 

 i iipulfes. lb. p. 14S. He alio adds, that what he calls 

 attraction may polhbly be efleCled by impulfe, though not 

 a common or corporeal impulfe, but after fome ether man- 

 ner unknown to us. Optics, p. 322. 



Attraclion indeed, if confidered as a quality arifing from 

 the fpecilic forms of bodies, ought, together with fympa- 

 thy, antipathy, and the whole tribe of occult qualities, to 

 be exploded. But when we have fet thefc afide, tlicre will 

 remain innumerable phenomena of nature, and particularly 

 the gravity or weight of bodies, or their tendency tc a cen- 

 tre, which argue a principle of aftion feemingjy dillinil 

 from impulfe, or where at leafl ' there is no fenliblc im- 

 pulfion concerned. It is alfo well known, that this adion 

 differs, in fome refpefts, from all impullion we know of, the 

 latter being always found to aft in proportion to tiie furface 

 of bodies ; whereas gravity afts according to their folid 

 contents ; and confequently mud arife from fome cauie 

 that penetrates or pervades their whole fubllances. Tliis 

 unknown principle, which can be confidered fo only with 

 rcfpeft to its caufe (for its phenomena and etltCls are moll 

 obvious), with all the fpecies and modifications of it, is 

 what we call attraiftion, which is a general name under 

 which all mutual tendencies, where no phyfical impulfe 

 appears, and which cannot therefore be accounted for trom 

 any inow.i laws of nature, may be ranged ; and here arife 



ATT 



fcvcral particular kinds of attradions, as gra\ity, magi.e- 

 tifm, cledricity, &c. which are fo many diffcrtnt laws ; 

 and only agreeing in this, that we do not fee any ph\-lical 

 caufes of them ; but that as to our fenfcs, tncy may really 

 arife from lome power or efncacy in fuch bodies, L) whicK 

 they are enabled to act, even upon diftant budici, though 

 our reafon abfolutely difallows of any fuch adio«. 



Attraction may be divided with rcfpcft to the law it 

 obferves, into two kinds: 1. That which extends to fenfi- 

 ble dillances ; fuch arc the attrdftions of gravity found in 

 all bodies ; and the attraclion of magnetilm and elcftricily 

 found in fome particular bodies; the fi-vcral Ia*s and phe- 

 nomena of which fee under iheir refpcclivc articles. 



Among thefc, the attradtion of gravity, wliich is alfo 

 called the centripetal force, is one of the grtatelt and moil 

 nniverfal principles in nature ; we fee and feel it operate 

 on bodies near the earth, and find by obfcrv.ition, that the 

 fame power alfo obtains in the moon, and in both the 

 primary and fecondary planets, as well a» iii the comets; 

 and that this is the power by which tiicy are all retained 

 ill their orbits, &c.: and hence, as gravity is found in all 

 the bodies which come under our obfer\ation, it is eafily 

 inferred, by one of the fettled rules of philufophizing, 

 that it obtains in all others ; and as it is found to be a» 

 the quantity of matter in each body, it muil -be in every 

 particle thereof; and hence, every particle in nature i» 

 proved to attrad every other particle, &c. Sec the demon- 

 ftiation of this laid down at large under ttie articles Cfs- 



TRIFUGAL, CENTRIPtTAL, CoMET, MoON, NeWT0SI.\S 



Phllofophy, Planet, Satellite, Sun, £cc. 



From this attradion arifes all the motion, and confj- 

 qucntly all the mutation, in the univerfe ; by this, hcivy 

 bodies defcend and light ones afceiid, projedilcs arc directed, 

 vapouis and exhalations arite, and rains, &c. fall. All.) 

 from 'he iame caufe rivers glide, the air prcffes, the ocean 

 fwells, &c. Ill cffed, the motions arifing from this prin- 

 ciple, make the fubjed of that extenfive branch of matlw 

 tics called Mcc'iniiics or Stulks, with the parts or append- 

 ages \.\\ereoi }{y<lroJla!ics, Pneumalia. See Mathematics, 

 Philosophy, he. 



2. That which extends only to fmall dillances. — Such is 

 found to obtain in the mlnnte particles whereof all bodies 

 are compcfed, which attrad each other at or extremely 

 near the point of contad, with a force much fuptriar to that 

 ot gravity ; but which at any dillance from it decreafcs 

 much fader tlian the power of gravity. This power is 

 known by the name ot the ytllraClion of CJiefnv, as being 

 that by wl'ich the atoms or infeiifible particles ot bodies arc 

 united with larger and more lenlible figures. SeeCoHEsioN. 



The latter kind of attraction owns Newton for its dif- 

 coverer, as the former docs for its improver. The laws of 

 motion, percnfiion, &c. in fenfible bodies under various 

 circurailances, as falling, projeded, S:c. afcertained by the 

 later philofophers, do not reach to thofe more remote in- 

 teftine motions of the component particles of the fame 

 bodies, on which the changes of their texture, colour, pro- 

 perties, &c. depend; fo that our philotophy, if it wert? 

 founded wholly on the principle of gravitation, and canied 

 no farther than that would lead us, would ntce(I;irily Lc 

 very deficient. 



But befidc the common laws of fenfible mafles, the mi- 

 nute parts which they are compofed of are found fubjec\ 

 to fome others which have been only of late taken notice of, 

 and arc yet verv impenfedly known. Newton, to whole 

 happy penetration we owe the hint, contents himlelf with 

 ellablilhing that there are fuch motions in the minima 

 nature, and that they flow from cert3i;i powers or forces 



cot 



