Some Farther Remarks on P. Souciet's Dissertations against Sir Isaac Newton's Chronology, by Edmund Halley, L.L.D. Astron. Reg. In a Letter to Dr. Jurin, Coll. Med. & S.R.Soc.

II. Some farther Remarks on P. Souciet's Dissertations against Sir Isaac Newton's Chronology, by Edmund Halley, L.L.D. Astron. Reg. In a Letter to Dr. Jurin, Coll. Med. & S.R.Soc. SIR, WHEN I gave you my Paper of Remarks on P. Souciet's Dissertations against Sir Isaac Newton's Chronology, I was oblig'd to take what he was pleas'd to give us out of Hipparchus's Comment on Aratus, not having then that Author himself by me. Since then, by the favour of a very good Friend, having gotten the Florence Edition of Hipparchus, Anno 1567, I find an Argument very much ad Hominem, which the R. P. must confess will bring the Argonautick Expedition full as low as Sir Isaac Newton makes it. P. Souciet in his fifth Dissertation, Page 119, 120, finds out a Star of the first Magnitude, close adjoining to that we now call the first Star of Aries, as it is in the Catalogue of Ptolemy, where it is said to be in the Horn of Aries, and not in the Ear. This Star the R.P. supposes long since to have disappeared; but that being of old very considerable, it was from this first Star of Aries, the Zodiack began, tho' tho' for Argument-sake he is contented to let it begin as Sir Isaac does, with the aforesaid Star in the Ear or Horn; which Hipparchus, in the last and 54th Page, tells us, in his time follow'd the Equinoctial Colure the 20th part of an Hour: And supposing the Star that has disappeared, to have been at that time precisely on the Colure, it must differ but 45 Minutes of Right Ascension therefrom: But how he comes to make the difference of Longitude 40 Minutes no way appears, and is gratis dictum. In Page 49 of the said Florence-Edition, Hipparchus, treating of the rising and setting of the Constellations, tells us, that that of Aries began to rise with 18 Degrees of Pisces in the Ecliptic, and was wholly risen with the 24th Degree of Aries, whilst the Zodiack past the Meridian from 23 Degrees of Sagittary to 14 Degrees of Capricorn: And again (Page 52) he says, that the Constellation of Aries began to set with the 29th Degree of Pisces, and was wholly set with the 26th Degree of Aries, whilst the Zodiack past the Meridian from 29 Degrees of Gemini to 29 Degrees of Cancer. He tells us also that it was the very same Star that both rose and set first in that Constellation, calling it ὁ ἐπὶ τῆς ἐγκεφάλου πόδος, Page 49: And again, Page 52 'tis named ὁ ἐπὶ τῶν ἐγκεφάλων ποδίων, or That in the Fore-feet of the Ram. This certainly is the Star P. Soucier would place on the Equinoctial Colure, and makes it long since to have disappeared; without enquiring whether the aforesaid Data were not abundantly sufficient to determine its place in the Zodiack at that time; and without regard to the odd uncouth Posture he must suppose the Constellation of Aries to be in, when he makes one or both of the Fore-feet so near to, and above the Horn or Ear. Hip- Hipparchus expressly says, that it rose when 23 Degrees of Sagittary was on the Meridian, and set when 29 Degrees of Gemini past it; and taking the middle between those Points, it is plain, that it culminated with about 26 Degrees of Pisces, and that it had North Declination; the Excess above 180 Degrees shewing that the Ascensional Difference was about 2 ½ Degrees. But to give the Argument its full Scope, the Right Ascension of 23 ½ of Sagittary (allowing Hipparchus his Obliquity 23° 51' 20") will be found 262° 54'. And that of 29 Degrees of Gemini will be 88° 54': So that this Star was above the Horizon (in the Latitude of 36 Degrees North; to which Hipparchus has adapted his Calculation) 12 Hours 24 Minutes or 186 Degrees; whence the Right Ascension of the Star is justly concluded 355 Degrees 54 Minutes; and its Ascensional Difference precisely 3 Degrees; which in that Latitude makes its Declination 4 Degrees 7 Minutes North. We have therefore gotten both the Right Ascension and Declination of this supposed first Star of Aries. Let us now see what Longitude and Latitude results from the aforesaid Right Ascension with 4 Degrees 7 Minutes North Declination, assuming the Obliquity with Hipparchus, to have been 23° 51' 20"; and we shall by a just Computation, find the Star at that time to have been in 27° 53' of Pisces, with 5° 24' North Latitude, which therefore was reckoned the place of the Star at that time by Hipparchus. Add 2° 40', for 265 Years between Hipparchus and Ptolemy, and we shall have its place, in Ptolemy's Account, Aries 2° 33', with 5° 24' North Latitude. But the 22d Star of Pisces in Ptolemy's Catalogue has the same Longitude and Latitude, with sufficient exact. a&ness, viz. Aries $0^\circ 40'$, with North Latitude $5^\circ 20'$, and is Media trium in Lino Boreo Piscium (n Bayero.) Hence it cannot be doubted but that this Star which P. Souciet takes to have been once a Star of the first Magnitude, was no other than the said 22th of Pisces, which in the British Catalogue, fitted to the Year 1690, is put down in Aries $22^\circ 29' \frac{1}{3}$ with North Latitude $5^\circ 21'$. How Hipparchus came to reckon this Star to be in the Fore-foot of Aries, does not at present appear; but it is not unlikely that these Commentaries of his upon Aratus were written some time before he set about making his Catalogue of the fixt Stars; when he might change his Opinion, and replace it in the Line of the Fishes, to which it seems more properly to belong. Be that as it will, we will for once, suppose with P. Souciet, this Star to have been in the beginning of the Zodiack, or of the Constellation of Aries, and that at the time of the first fixing the Colures, that of the Vernal Equinox past 15 Degrees in Consequence thereof. Now anno ineunte 1690, this Star being in Aries $22^\circ 29' \frac{1}{3}$, if we add thereto 15 Degrees, we shall have Taurus $7^\circ 29' \frac{1}{3}$ for the Point in the Ecliptic that was then the beginning of the Zodiack. Now $37 \frac{1}{2}$ Degrees, at 50 Seconds per Annum, gives 2700 Years; from which deducting 1690, we shall have 1010 Years before Christ. But this Star having $5^\circ 21'$ North Latitude, the Colure, when it past over it, intersected the Ecliptick in $2^\circ 20'$ less Longitude, which gives the time 168 Years later, or but $8\frac{1}{2}$ Years before Christ. So that malgré cette grande découverte, the new System of Chronology is so far from being refuted, that it seems to be very much con- confirmed thereby, at least in the Opinion of the R. Pere. I have assumed the Latitude to which Hipparchus might have adapted his Calculations, to be 36 Degrees; because I find in Page 14 of the aforesaid Edition that he makes the longest Tropical Day 14 h. 30': And in Page 29, he tells us, that the Southern Star in the left Foot of Bootes (υ Bayero) having 27° 20' North Declination, was above the Horizon, 14 h. 57'; whence it follows, that the Latitude must be 36° 5'. He also tells us, in the same Page 29, that this Star set when 22° of Capricorn culminated, and 6° of Taurus ascended; repeating the same thing in Pag. 39, which leaves no room to suspect that those Numbers are not the same that Hipparchus had computed. I therefore thought it worth while to enquire in what Latitude 6 Degrees of Taurus rises when 22 Degrees of Capricorn is on the Meridian; and with the Obliquity of the Ecliptick, as now we have it, the Latitude resulting is 35° 1'. North; but with the Obliquity allowed by Hipparchus, it will be found less than 35°. This I say, only to obviate any Objection that may be made by P. Souciet to the aforegoing Argument; tho' if he pleate to examine it, he will find that an Error of a Degree in the assumed Latitude, will by no means invalidate the Proof here given that this First Star of Aries could be no other than the middle Star in Lino Boreo Piscium, marked n by Bayer.