applying to them the fame Forces and Mathematical calculations, for the phænomena

Without detracting from the merit of Sir Ifaac Newton as an Aftronomer, which is fo great that nothing can diminish it, truth and justice require it should be acknowledged, that the Application of Projectile to Celestial Motion, which he improved to fuch wonderful and important purposes, was made by one before him.

'Certiffimum hoc eft et ab omnibus conceffum, motum 'Planetarum verum nec effe perfecte circularem, neque 'perfecte æqualem. Teftantur enim obfervationes, idque 'ultra omnem difputationem, figuram orbitæ planetariæ 'effe Ellipticam five ovalem, et a circulo deficientem; 'motumque ejus in hoc Elliptico inæqualem effe, et pro 'diftantia fua a Sole intendi ac remitti.-Ultro fe offerunt 'caufæ Phyficæ et naturales, quæ talem motum neceffi'tate Geometrica defcribunt.-Per caufas Phyficas veritati 'fatisfaciamus; ut enim Planeta legibus magneticis moveatur, quid quæfo impedit, cum idem in aliis exemplis * aperte videamus ? — Projiciatur plumbum aliquod in altum, furgit primo velociter, deinde tardius, dum tandem Rationarium in terram recidat continuo velocitatis incre'mento, atque ita motum librationis defcribit.-Oritur ea 'libratio in linea recta ex pugna virtutis illius quam manus 'tua illi infudit, una cum virtute telluris magnetica, qua omnia gravia ad fe attrahit, ut magnes ferrum. Nihil

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opus eft, ut circulos nefcio quos in ære fomniemus, 'ubi caufam naturalem ante oculos habemus. Et quæfo 'quid eft quod in motu Planetarum, ubi eadem commo'ditas non deeft, caufam veram a Natura ipfa tot exemplis confirmatum, fictitio circulorum fomnio commutare'mus.' Jeremiæ Horroccii Liverpolienfis Opera Pofthuma Difp. vi. cap. I.

When

of which they moft exactly and wonderfully accounted.

When we compare this extract with that above, and indeed with the whole plan of his Principia, we cannot help concluding that Sir Ifaac Newton made these broad and pointed hints of Mr. Horrockes, the bafis of his Aftronomy. He acknowledges this philofopher, who died about the year that he was born, to have been the first who difcovered the Moon's motion to be in an ellipfe about the Earth in the lower focus; and that this invention was improved by Halley, who put the center of the Ellipfe in an Epicyle with its center revolving uniformly about the Earth, from whence the inequality of the progress and regrefs of the apogee, and in the quantity of eccentricity is deduced. [See Princip. lib. iii. prop. 35 Schol.] The philofophical tract alluded to by Sir Ifaac is entitled Nova theorea Luna published after the author's death by Dr. Wallis; and in the fame publication is that other tract De Motu Siderum, from which the extract above is taken, and which our great Aftronomer muft undoubtedly have seen, as he was particularly converfant with every thing that came from or through the hands of Dr. Wallis.

This philofopher was the first who, in 1639, after detecting the fallacies of the Lambergian tables and correcting them, by the ufe of Kepler's which he improved, calculated and took the obfervation of that rare and decifive Phænomenon the Tranfit of Venus, in which Kepler had failed. This important observation, by which the Sun's parallax and distance from the Earth are more justly afcertained, he published in a work entitled De Venere in Sole vifa, a few weeks before his death; and he had a much greater work in band in which he had made confiderable progrefs. The fubject of this was, in the first part, to

refute

By this theory founded and established in Projectile Motion, and thence, by a vast ex

refute the hypothefes of Lamberg by which he had been mifled; which is the work collected and published by Dr. Wallis And the fecond part was much more important intending to found a NEW PHILOSOPHY upon the basis of found Experiment and accurate Obfervation, in which he adopted the Keplerian hypotheses corrected and improved. But, though he had made fuch advances in this New Philofophy as from it to calculate and conftruct an Ephemeris, he had not so adjufted his materials and committed them to paper, that they could be collected and arranged for publication. An idea of his general scope may, however, be collected from what is incidentally said in the tract De motu Siderum inferted in the publication mentioned above. 'Caufa vera eft phyfica, Sol nempe converfione fui cor'poris reliquos planetas legibus magneticis fecum rapit in 'gyrum, non aliter quam Terra Lunam, nubes, et reliqua in altum projecta, màgnetica hac virtute fecum circumvehit, ut doctiffime probat Keplerus. Caufam autem Ex'centricitatis male (ut mihi videtur) tradit. Illam ego 'fibris magneticis quas ille in corpore Planetarum fingit. 'tribuendam non cenfeo, fed inertia eorum corporali, qua 'locum fuum tueri conantur adverfus fortiorem Solis vir'tutem. Philofopham hanc alio tempore fufius exponam, ejufque ope fperare aufim, ipfum Creationis momentum 'ex motibus cœleftibus (faltem probabiliffime) demon'ftrare. In prefens hoc ago ut ftudiofiorum animos a vanis 'illis et fictitiis circulorum fomniis ad naturalem et phy'ficam magis caufarum difquifitionem revocarem.- Ex'empla multa dari poffunt eorum quæ per leges naturales 'et magneticas in circuitum rapiuntur.-Videmus Ter'ram magnetica fua vi nubes et reliqua furfum projecta • abripere

ertion of mind, tranflated to Celestial, he confirmed the obfervations of these philofo

abripere in gyrum.-Docet igitur hic nos experientia fi'guram circularem per leges magneticas generari posse, ' cur illud de ftellis dubitemus, quod in aliis verum cernimus ?- Oftendimus nos Philofophiæ noftræ familiare exemplum.-Philofophiam noftram ab ipfa Natura ultro oblatam nos grati accepimus: fruftra illi ad caufas fictitias, et pro lubitu commentas confugiunt.'

That every philofopher has an abfolute right to avail himself of the labours and difcoveries of his predecessors, as a legacy freely given him, is a privilege which philofophy always claims. It is, however, a tribute juftly due to the memory of this extraordinary genius, whilft we regret the lofs of his more valuable works, to acknowledge from what has been faved; that he was principally inftrumental in calling Philofophy out of the regions of fictitious invention, and putting her on the investigation of the phyfical Caufes of things from Experiments and Obfervations; that he not only made the application of Projectile Motion to the analogical illustration of Celestial, but also affigned the Forces both Projective and Attractive on which all geometrical calculations are founded; and that, without injuring the immortal fame of his great fucceffor, he may be fairly confidered as the Forerunner of Newton. He mentions the Vis Inertia of matter in totidem verbis: and as to the attractive force whether it be that of Magnetifm or Gravitation, is immaterial; and, indeed Sir Ifaac himself, in the beginning of his Principia, is quite indifferent both as to its name and nature (vel Vi Gravitatis, fi modo gravis fit Luna, vel alia quacumque Vi, quâ in Terram urgeatur.)

That every body refpecting the Earth as its center, and that every body respecting the Sun as its center and

phers; demonftrated their hypotheses and conjectures; and enacted, on a found found

moving in a sphere, are acted upon and varied in their motions and fpheres, according to their respective diftance, by fome phyfical caufe or caufes from which their phænomena could be geometrically demonftrated, was the general doctrine of Horrockes. Halley, obferving the surfaces of the planetary fpheres to be as the fquares of their radii, found the force at several distances to act reciprocally as the fquares. And Newton demonftrated that a planet must revolve in an ellipfis about the center of force in the lower focus acting reciprocally as the fquare of the distance, and that, with a radius drawn to that center, it must describe areas proportionable to the times; particularizing and completing the Mathematical Calculation, and carrying it through all the celestial phænomena. All which might, probably, have been done by Horrockes, had he lived to execute his work: but this excellent young man, of il luftrious genius but of humble birth, died in the year 1641 at the age of twenty three !!

Kepler's firft Rule is That the fame Planets describe equal areas in equal times:' and Sir Ifaac Newton demonftrated from thence That the Planets are attracted 'towards the Sun as their center. Kepler's fecond Rule is 'That the fquares of the periodical times are as the cubes of the tranfverfe axis of their orbits and Sir Ifaac demonftrated That the force is reciprocally as the fquares of the 'diftance; from which duplicate ratio he demonftrated 'the rule.' Kepler's third Rule is That the Orbits of the Planets are oval and probably elliptical, having the Sun in the focus and Sir Ifaac demonftrated that the Orbits are really elliptical And that the Sun is in the lower focus.