# Reflections upon Ancient and Modern Learning/Chapter 23

CHAP. XXIII.
Of Ancient and Modern Astronomy, and Opticks.
HAving now gone through with the several Parts of Natural History, I am to enquire into the State of Physico-Mathematical and Physical Sciences: Such as Astronomy, Opticks, Musick and Medicks. I put Astronomy first, because of the vast Extent, and real Nobleness of its Subject; and also because it has suffered the least Eclipse of any part of Knowledge whatsoever in the barbarous Times: For when the Greeks neglected it, the Arabs, and from them the Spaniards took it up. That this Enquiry might be the more exactly made, and that you might be throughly convinced of the Truth in this Matter, to which chiefly our Obligation lies, Mr. Edmond Halley, whose Labours towards the Advancement of this Science, have made him famous in so many distant Parts of the World, did me ​the Favour to communicate this following Paper.
'As for the Astronomy of the Ancients, this is usually reckoned for one of those Sciences wherein consisted the Learning of the Egyptians; and Strabo expresly declares, That there were in Babylonia several Universities, wherein Astronomy was chiefly professed; and Pliny tells us much the same thing: So that it might well be expected, that where such a Science was so much studied, it ought to have been proportionably cultivated. Notwithstanding all which it does appear, That there was nothing done by the Chaldæans older than about CCCC Years before Alexander's Conquest, that could be serviceable either to Hipparchus, or Ptolemee in their Determination of the celestial Motions: For had there been any Observations older than those we have, it cannot be doubted but the victorious Greeks must have procured them, as well as those they did, they being still more valuable for their Antiquity. All we have of them is only Seven Eclipses of the Moon, preserved in Ptolemee's Syntaxis; and even those, but very coursely set down, and the oldest not much above 700 Years before Christ, so that ​after all the Fame of these Chaldæans, we may be sure they had not gone far in this Science; and though Callisthenes be said by Porphyry to have brought from Babylon to Greece, Observations above MDCCCC Years older than Alexander, yet the proper Authors making no Mention, or Use of any such, renders it justly suspected for a Fable. What the Egyptians did in this Matter is less evident, no one Observation made by them being to be found in their Countryman Ptolemee, excepting what was done by the Greeks of Alexandria, under CCC Years before Christ. So that whatever was the Learning of these Two ancient Nations as to the Motions of the Stars, it seems to have been chiefly Theorical, and I will not deny but some of them might very long since be apprized of the Sun's being the Center of our System, for such was the Doctrine of Pythagoras, and Philolaus, and some others who were said to have travelled into these Parts.
From hence it may appear, That the Greeks were the first practical Astronomers, who endeavoured in earnest to make themselves Masters of the Science, and to whom we owe all the old Observations of the Planets, and of the ​Equinoxes and Tropicks, Thales was the first that could predict an Eclipse in Greece, not DC Years before Christ, and without doubt it was but a rude Account he had of the Motions; and 'twas Hipparchus who made the first Catalogue of the Fix'd-Stars, not above CL Years before Christ, without which Catalogue there could be scarce such a Science as Astronomy, and it is to the Subtilty and Diligence of that great Author, that the World was beholding for all its Astronomy for above MD Years. All that Ptolemee did in his Syntaxis, was no more but a bare Transcription of the Theories of Hipparchus, with some little Emendation of the periodical Motions, after about CCC Years Interval; and this Book of Ptolemee's was without Dispute, the utmost Perfection of the Ancient Astronomy, nor was there any thing in any Nation before it comparable thereto; for which Reason all the other Authors thereof were disregarded and lost; and among them Hipparchus himself. Nor did Posterity dare to alter the Theories delivered by Ptolemee, though successively Albategnius and the Arabs, and after them the Spanish Astronomers under Alphonsus, endeavoured to amend the Er​rors they observed in their Computations. But their Labours were fruitless, whilst from the Defects of their Principles, it was impossible to reconcile the Moon's Motion within a Degree, nor the Planets, Mars and Mercury, to a much greater Space.
Now in this Science to compare the Ancients with the Moderns, and so make a Parallel as just as may be, I oppose the Noble Tycho Brahe, or Hevelius to Hipparchus, and John Kepler to Claudius Ptolemee; and I suppose no one acquainted with the Stars will doubt, That the Catalogue of the Fix'd-Stars made by Tycho Brahe, about C Years since, does beyond Competition far excel that of Hipparchus, being commonly true to a Minute or Two, when the other many times fails half a Degree, both in Longitude and Latitude; and this is the fairlier carried, for that it was as easie for Hipparchus to observe the Fixd'-Stars, as for Tycho, or Hevelius, had he made Use of the same Industry and Instruments, the Telescope wherewith we now observe to the utmost possible Nicety, being equally unknown to Tycho as to Hipparchus, and not used by Hevelius. But what may justly be expected from Monsieur Cassini and Mr. Flamsteed in ​this Matter, does yet further advance in preciseness, as not capable to err half a mioute, though made with Instruments (w) p. 57.(w) of the Production of Gresham. As to the other Comparison between Kepler and Ptolemee, I question not but all that can judge, will be fully convinced that the Hypothesis of Eccentricks, and Epicycles introduced by the Ancients only to represent the Motions, and that but coursely too; with the Opinion of Ptolemee himself thereon, that the natural Motions were otherwise performed, ought not to be valued against that elegant Theory of the planetary Motions, first invented by the acute Diligence of Kepler, and now lately demonstrated by that excellent Geometer Mr. Newton, viz. That all the Planets move in Elliptick Orbs about the Sun, at whose Center, being placed in one Focus of the Ellipse, they describe equal Area's in equal times; this, as it is the necessary result of the Laws of Motion and Gravity, is also found rigorously to answer to all that is observed in the Motions, so that the Moderns may, with as much Reason as in any other Science whatsoever, value themselves on their having improved, I had almost said perfected, this of Astronomy.
​Optical Instruments have been so serviceable in the Advancement of Astronomy, that the Sciences which demonstrate their wonderful Properties ought next to be considered. Here also I must own my Obligation to Mr. Halley for this following Account of what the Ancients have done in them, and how much they have been out-done by Modern Mathematicians.
I suppose there are few so thorough-paced Fautors of Antiquity, as to brag much of their Skill, either in Opticks, or Dioptricks. Their Want of Opticks appears in their Want of Authors treating thereon; and yet much better in their Want of Ordonnance, (as it is called) in their Paintings, and Basse Relieve's, as has been already said in its proper Place. And as to Dioptricks, though some of the Ancients mention Refraction as a natural Effect of transparent Media, yet Des Cartes was the first who, in this Age, has discovered the Laws of Refraction, and brought Dioptricks to a Science. And the Invention of Telescopes and Microscopes; which must be wholly allowed to this Century, has received no small Improvements from the Study and Charge of Sir Paul Neile, and some other Members of Gre​sham. And these are such Instruments of real Knowledge, that though we will allow the Ancients to have done all that great Genii, with due Application, could arrive at; yet, for want of them, their Philosophical Argumentation could not come up to the present Pitch; not being able to fathom the boundless Depths of the Heavens, nor to unravel the Minutiæ of Nature, without the Assistance of the Glasses we are now possessed of'.
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