experiments and obfervations, to be the fame in both instances; that the Principles or general Laws, mathematically established from the Forces of the one, are transferred to the Phænomena of the other; and that the proofs and operations deduced from these Principles, in the latter cafe, are confirmed by Facts, and Experience, the first and final test of truth. And it is enough for his immortal honour, that his Aftronomy, thus founded on Mechanics, has anticipated and predicted all the ftupendous revolutions of the hea

cond causes either different in themselves, or compounded differently, from those which act upon Projectiles, as no experiments can be inftituted in these diftant regions, are points worthy the confideration of a philosopher.

But there are many motions upon the earth different from that of projectiles, which may probably lay the foundation of an Analogy to the celeftial motions; as that of Fire, which is directly oppofite to Gravitation. We have heard of a foreigner, who is projecting an Aftronomy on the principle of Repulfion: and our own countryman, the ingenious Mr. Jones, has affigned a principle of Planetary motion grounded on Experiment totally different from the Newtonian Forces; and which, if the real caufes are to be given, is much more fimple, and, in many refpects, lefs objectionable. [See his Effay on the Principles of Natural Philofophy.]

vens; that it has furmounted innumerable difficulties, and demonftrated what was before out of the reach of human obfervation; and that it has erected, upon a mathematical conviction, all thofe celeftial facts and obfervations into a fyftem at once fublime and luminous.

Had this great and good man been content to reft his Aftronomy on the bafis of this ANALOGY Confirmed by repeated Facts and uniform Experience; and left the Caufes of the celeftial motion to HIM, many of whose ways are above all human investigation, his philofophy would have maintained the fame dignity and value, equally useful

P The ANALOGY, on which Aftronomy is founded, concerns properly the Phænomena and apparent Effects, and need not, perhaps cannot, ever extend to the real Causes. And Dr. Clarke, the learned advocate and defender of Newton, in his conteft with Leibnitz, after many a ftruggle, was obliged to bring the matter at laft to this fame iffue; where he says, That 'Attraction is not a Cause, but a Phænomenon or Effect difcovered by experience, whatever be the Caufe of it, to which mathematical calcu'lations are usefully applied.' p. 355 and 356.

to

to all the purposes of civil and focial life, and equally acceptable to the contemplative student; without being involved in those abfurdities and incumbered with thofe difficulties, which even the genius of a Newton was unable to furmount, and which his followers have laboured in vain to evade or palliate; without being fo liable to be abused

To establish his Projection or Centrifugal Force, ac cording to his firft Axiom, he was obliged to invent a perfect Vacuum: But then, for his Gravitation or Centripetal Force a Vacuum would not do; and he was brought to great difficulties, [See his letter to Dr. Bentley] and at laft to the neceffity of conjecturing a fubtle ethereal fluid, as a medium, to pervade the universe : [See Opt. Quæft. 18, 19, 20, 21.] And thus, fays Mr. Jones, he folved the 'government of the created world by a Noftrum, which ' hath never yet been understood.'

'In juftice to the Newtonian Philofophy I cannot avoid tranfcribing the Apology, made in the Recenfion of the Controverfy with Leibnitz, from its laft and ableft Edition; as it contains the fubftance of the defence adopted by the followers of Newton.

Philofophia porro, quam in Principiis fuis atque Opticis Newtonus excoluit, eft experimentalis illa fcilicet, quæ caufas rerum non fidentius docet, quam per experimenta confirmari queant; neque implenda eft opinationibus, quæ per phænomena nequeunt probari. Et idcirco

and perverted, by the artful and evil inventions of the human mind, to oblique and

in Opticis fuis, res experimentis firmatas ab illis quæ incertæ adhuc manent diftinxit Newtonus; et incertas aliquot ejufmodi, fub finem Opticorum, ut quærenda propofuit. Eandemque ob caufam, in Principiorum præfatione cum memoraffet motus planetarum, cometarum, lunæ ac maris, ceu in libro illo de Gravitatis Theoria deductos, hæc addidit: Utinam cætera naturæ phæno'mena ex Principiis Mechanicis, eodem argumentandi · genere, derivare liceret. Nam multa me movent, ut nonnihil fufpicer, ea omnia ex viribus quibufdam pen' dere poffe, quibus corporum particulæ, per caufas non'dum cogitas, vel in se mutuo impelluntur, et fecundum ' regulares figuras cohærent, vel ab invicem fugantur, et recedunt: quibus viribus ignotis, philofophi hactenus ❝ naturam fruftra tentarunt.' Et fub finem ejus libri, in fecunda editione narrat; ut, præ inopia experimentorum tanto negotio fufficientium, non aggreffus fit leges actionum illius fpiritus, five agentis, defcribere, per quem efficitur hæc attractio. Quin et eandem ob caufam de Gravitatis caufa nihil pronunciat; quod nulla experimenta, five phænomena, ad manum effent, quæ caufam illam certo indicare poffent. Atque hoc in Principiis fuis, fub ipfo initio, abunde declaraverat, his verbis: Virium 'caufas et fedes phyficas jam non expendo.' Et paulo poft: 'Voces Attractionis, Impreffus, vel Propenfionis cujuf'cunque in centrum, indifferenter et pro fe mutuo pro'mifcue ufurpo; has vires, non phyfice, fed mathematice • tantum confiderando. Unde caveat lector, ne per hùjufmodi voces cogitet me fpeciem vel modum actionis, 'caufamve aut rationem phyficam alicubi definire; vel 6 centris, quæ funt puncta mathematica, vires vere et ' phyfice

finifter purposes; and without being made objective to the principles and doctrines of

phyfice tribuere ; fi forte aut centra trahere, aut vires 'centrorum effe dixero.' Et fub finem Optices: Qua 'caufa efficiente hæ attractiones' [fc. gravitas, vifque * magnetica et electrica] peragantur, hic non inquiro. Quam ego attractionem appello, fieri fane poteft, ut ea 'efficiatur impulfu ; vel alio aliquo modo nobis incognito. 'Hanc vocem attractionis ita hic accipi velim, ut in uni' verfum folummodo vim aliquam fignificare intelligatur, qua corpora ad fe mutuo tendant; cuicunque demum 'caufæ attribuenda fit illa vis: nam ex phænomenis naturæ illud nos prius edoctos effe oportet, quænam corpora fe invicem attrahant, et quænam fint leges et proprietates iftius attractionis, quam in id inquirere par fit, ' quanam efficiente caufa peragatur attractio.' Pauloque inferius, eafdem attractiones tanquam vires confiderat, quas in rerum natura exiftentiam habere, licet caufæ earum nondum fint cognitæ, per phænomena conftat; diftinguitque eas a qualitatibus occultis, que a fpecificis rerum formis fluere exiftimantur. Et in fcholio fub extremum Principiorum, cum gravitatis proprietates memoraffet, hæc addidit: Rationem vero harum Gravitatis 'proprietatum ex phænomenis nondum potui deducere ; 'et hypothefes non fingo. Quicquid enim ex phænomenis 'non deducitur, hypothefis vocanda eft; et hypothefes, feu metaphyficæ, feu phyficæ, feu qualitatum, occulta'rum, feu mechanicæ, in philofophia experimentali locum ' non habent.-Satis eft, quod Gravitas revera existat et agat fecundum leges a nobis expofitas, et ad corporum 'cœleftium et maris noftri motus omnes fufficiat.' Jam vero poft hæc omnia, quæ confulto præmonuerat Newtonus, quis non miretur, ideo eum a quoquam fugillari,

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