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applying to them the same Forces and Mathematical calculations, for the phænomena
Without detracting from the merit of Sir Isaac Newton as an Astronomer, which is so great that nothing can diminish it, truth and justice require it should be acknow. ledged, that the Application of Projectile to Celestial Motion, which he improved to such wonderful and important purposes, was made by one before him.
Certiffimum hoc eft et ab omnibus concessum, motum * Planetarum verum nec effe perfecte circularem, neque perfecte æqualem. Teftantur enim observationes, idque
ultra omnem disputationem, figuram orbitæ planetariæ Selle Ellipticam five ovalem, et a circulo deficientem ; 'motumque ejus in hoc Elliptico inæqualem esse, et pro
diftantia fua a Sole intendi ac remitti.-Ultro se offerunt caufæ Physicæ et naturales, quæ talem motum necessi.
tate Geometrica describunt.- Per caufas Physicas veritati * fatisfaciamus; ut enim Planeta legibus magneticis moveatur, quid quæso impedit, cum idem in aliis exemplis aperte videamus ? - Projiciatur plumbum aliquod in altum, surgit primo velociter, deinde tardius, dum tandem Jiationarium in terram recidat continuo velocitatis incre* mento, atque ita motum librationis describit.- 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 • hic opus eft, ut circulos nescio quos in ære somniemus, ubi causam naturalem ante oculos habemus. Et quæso quid eft quod in motu Planetarum, ubi eadem commoditas non deest, causam veram a Natura ipsa tot exemplis confirmatum, fictitio circulorum fomnio commutaremus.' Jeremiæ Horroccii Liverpoliensis Opera Pofthuma Disp. vi. cap. 1.
of which they most 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 Isaac Newton made these broad and pointed hints of Mr. Horrockes; the basis of his Aftronomy. He acknowiedges this philosopher, who died about the year that he was born, to have been the first who disa covered the Moon's motion to be in an ellipse about the Earth in the lower focus; and that this invention was improved by Halley, who put the center of the Ellipse in an Epicyle with its center revolving uniformly about the Earth, from whence the inequality of the progress and regress of the apogee, and in the quantity of eccentricity is deduced. [See Princip. lib. iii. prop. 35 Schol.1 The philosophical tract alluded to by Sir Isaac is entitled Nova theorea Lunæ published after the author's death by Dr. Wallis ; and in the same publication is that other tract De Motu Siderum, from which the extract above is taken, and which our great Astronomer must undoubtedly have seen, as he was particularly conversant with every thing that came from or through the hands of Dr. Wallis.
This philosopher was the first who, in 1639, after de. tecting the fallacies of the Lambergian tables and correcting them, by the use of Kepler’s which he improved, calculated and took the observation of that rare and decisive Phænomenon the Transit of Venus, in which Kepler had failed. This important observation, by which the Sun's parallax and distance from the Earth are more justly ascertained, he published in a work entitled De Venere in Sole visa, a few weeks before his death; and he had a much greater work in hand in which he had made considerable progress. The subject of this was, in the first part, to
By this theory founded and established in Projectile Motion, and thence, by a vast ex.
refute the hypotheses of Lamberg by which he had been mis. led; which is the work collected and published by Dr. Wallis : And the second part was much more important intending to found a New PHILOSOPHY upon the basis of sound Experiment and accurate Observation, in which he adopted the Keplerian hypotheses corrected and improved. But, though he had made such advances in this New Philosophy as from it to calculate and construct an Ephemeris, he had not so adjusted his materials and committed chem 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 metu Siderum inserted in the publication mentioned above.
Causa vera est phyfica, Sol nempe conversione sui cor'poris reliquos planetas legibus magneticis secum rapit in
gyrum, non aliter quam Terra Lunam, nubes, et reliqua in altum projecta, magnetica hac virtute secum circum"vehit, ut doctisfime probat Keplerus. Causam autem Excentricitatis male (ut mihi videtur) tradit. Illam ego fibris magneticis quas ille in corpore Planetarum fingit tribuendam non cenfeo, sed inertiæ eorum corporali, qua
locum suum tueri conantur adversus fortiorem Solis vir'tutem. Philosopham hanc alio tempore fufius exponam,
ejusque ope sperare aufim, ipsum Creationis momentum 'ex motibus caeleftibus (faltem probabiliflime) demon'ftrare. In presens hoc ago ut studiosiorum animos a vanis
illis et fictitiis circulorum somniis ad naturalem et phy' ficam magis causarum disquisitionem revocarem.- Exrempla multa dari possunt eorum quæ per leges naturales
et magneticas in circuitum rapiuntur.-Videmus Ter. ‘ram magnetica sua vi nubes et reliqua sursum projecta
ertion of mind, translated to Celestial, he confirmed the observations of these philoso
abripere in gyrum.-Docet igitur hic nos experientia fic ‘guram circularem per leges magneticas generari pofle, 'cur illud de ftellis dubitemus, quod in aliis verum cerni
mus? - Oftendimus nos Philofophiæ noftræ familiare • exemplum.-Philosophiam nostram ab ipsa Natura ultro
oblatam nos grati accepimus : frustra illi ad caufas fic(tițias, et pro lubitu commentas confugiunt.'
That every philosopher has an absolute right to avail himself of the labours and discoveries of his predecessors, as a legacy freely given him, is a privilege which philosophy always claims. It is, however, a tribute justly due to the memory of this extraordinary genius, whilst we regret the loss of his more valuable works, to acknowledge from what has been saved ; that he was principally inftrumental in calling Philosophy out of the regions of fictitious invention, and putting her on the investigation of the physical Causes of things from Experiments and Observations ; that he not only made the application of Projectile Motion to the analogical illustration of Celestial, but also assigned the Forces both Projective and Attractive on which all geometrical calculations are founded; and that, without injuring the immortal fame of his great successor, he may be fairly considered as the Forerunner of Newton. He mentions the Vis Inertiæ of matter in totidem verbis : and as to the attractive force wheiher it be that of Magnetism 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 sit Luna, vel alia quacumque Vi, quâ in Terram urgeatur.)
That every body respecting the Earth as its center, and that every body respecting the Sun as its center and
phers; demonstrated their hypotheses and conjectures ;' and enacted, on a sound found
moving in a sphere, are acted upon and varied in their motions and spheres, according to their respective distance, by some physical cause or causes from which their phænomena could be geometrically demonstrated, was the general doctrine of Horrockes. Halley, observing the surfaces of the planetary spheres to be as the squares of their radii, found the force at several distances to act reciprocally as the squares. And Newton demonstrated that a planet must revolve in an ellipsis about the center of force in the lower focus acting reciprocally as the square 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 ile luftrious genius but of humble birth, died in the year 1641 at the age of twenty three !!
· Kepler's firft Rule is • That the same Planets describe fequal areas in equal times :' and Sir Isaac Newton demonstrated from thence · That the Planets are attracted
towards the Sun as their center. Kepler's second Rule is "That the squares of the periodical times are as the cubes of
the transverse axis of their orbits :' and Sir Isaac demonftrared • That the force is reciprocally as the squares of the . diftance; from which duplicate ratio he demonstrated
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 Isaac demonstrated that the Orbits are really elliptical "And that the Sun is in the lower focus.