CHAPTER XV OF THE REVOLUTION OF THE PLANETS ABOUT THEIR OWN AXIS.

1.  HOW useful an aid the invention of telescopes bath been to the astronomical observations of the moderns, is particularly evident from their discovery, that the planets revolve on their axis; a discovery founded on the periodical revolution of the spots observed on their disks: so that every planet performs two revolutions, by the one of which it is carried with others about a common centre; and by the other moves upon its axis round its own. But all that the moderns have advanced in this respect, serves only to confirm to the ancients the glory of being the first discoverers. The moderns are in this to the ancients, as the French Philosophers are to Sir Isaac Newton, all whose Labours and travels in visiting the poles and equator to determine the figure of the earth, serve only to confirm what Sir Isaac had thought of it, without so much as stirring from his closet. in the same manner, we have proved, that most of our experiments have served, and do still contribute to confirm and support the conjectures of the ancients; although it bath often happened, that those very conjectures of theirs, which are now so generally received as true, have formerly been as generally decried. Of this we have had instances in the preceding chapter, and the present will exhibit another not less remarkable.

2.   Whatever were the arguments upon which the ancients founded their theory, certain it is, they clearly apprehended, that the planets revolved upon their own axis.. Heraclides of Pontus, and Exphantus, two celebrated Pythagoreans, intimated this truth long ago, and made use of a very apt comparison to convey their idea, saying, that the earth turned from west to east, just as a wheel does upon its axis or centre. And Plato extended this observation from the earth to the other planets; for, according to Atticus, the Platonic, who explains his opinion, “to that general motion which makes the planets describe a circular course, he added another resulting from their spherical shape, which made each of them move about its own centre, whilst they performed the general revolution of their course.” Plotinus also ascribes this sentiment to Plato, for speaking of him, he says, that besides the grand circular course observed by all the stars in general, he thought “they each performed another about their own centre.”

3.  Cicero ascribes the same notion to Nicetas of Syracuse, and quotes Theophrastus to warrant what he advances ; this is he whom Diogcnus Laertius names Hycetas, whose opinion was, that the celerity of the earth’s motion about its own axis, and otherwise, was the only cause of the apparent revolutions of the heavenly bodies.

4.  Our secondary planet, the moon, gave the ancients an opportunity of displaying their penetration. They early discovered, that it had no light of its own, but shone with that which it reflected from the sun. This, after Thales, was the sentiments of Anaxagoras and of Empedocles, who thence accounted not only for the mildness of its splendour, but the imperceptibility of its heat; which our experiments confirm: for with all the aid of burning glasses, we have never yet found it practicable to produce the least effect of heat from any combination of its rays.

5.   The observations made by the moderns, tend to persuade us, that the moon has an atmosphere, though very rare. In a total eclipse of the sun, there appears about the disk of the moon, a glimmering radiance, parallel to its circumference, which becomes more arid more extenuated or rare, as it diverges from it. This, perhaps, is no other than an effect proceeding from such a fluid as air; which by reason of its weight and elasticity, is rather more dense at bottom than at top. With a telescope we easily discern in the moon, parts more elevated and more bright than others, which are judged to the mountains. We discern also other parts lower and less bright, which seem to be vallies lying between those mountains. And there are other parts, which reflecting less light, and presenting one uniform, smooth surface, are supposed to be large pieces of water. If the moon then has its collections of water, its atmosphere, its mountains and its vallies ; it is thence inferred, that there may also be rain there, and snow, and all the other aerial commotions natural to such a situation, and our idea of the wisdom and power of God intimates to us, that he may have placed creatures there to inhabit it ; rather than that all this display of his skill should be a mere waste.

6.  The ancients, who had not the aid of telescopes, supplied the defect of that instrument by a vivacity of’ penetration; for, without the means that we have, they have deduced all those consequences that are admitted by the moderns: and discovered long before by the mental eye, whatever bath since been presented to corporeal sight through the medium of telescopes.

7. We see by some fragments of theirs, in how sublime a manner and worthy of the majesty of the deity, they entered into the views of that Supreme Being, in his destination of the planets, and that multitude of stars placed by him in the firmament. They looked upon them as so many suns, about which rolled planets of their own, such as those of our solar system. Nay they went farther, maintaining that those planets contained inhabitants, whose natures they presume not to describe, though they suppose them to yield to those’ of ours, neither in beauty nor in dignity. Orpheus is the most ancient whose Opinion on this subject hath come down to us. Proclus presents us with three verses of that ancient philosopher, wherein he positively asserts, that the moon was another earth, having in it mountains, vallies, &c. 

8.   Pythagoras, who followed Orpheus in many of his opinions, taught likewise, that the moon was an earth like ours, replete with animals, whose nature he presumed not to describe, though be was persuaded, they were of a more noble and elegant kind than ours, and not liable to the same infirmities.

9.  It were easy here to multiply quotations, and show, by a cro!d of passages, that this opinion was very common among the ancient philosophers ; but I shall content myself with adding a remarkable passage of Stoboeus, wherein he gives us Democritus’s opinion about the nature of the moon, and the cause of those spots which we see upon its disk. That great philosopher imagined, that those spots were no other than shades, formed by the excessive height of the lunar, mountains, which intercepted the light from the lower parts of that planet, where the vallies formed themselves into what appeared to us. as shades or spots. Plutarch went farther, alleging, that there were ernbosomed in the moon, vast seas and profound caverns. These, his conjectures, are built upon the same foundation with those of the moderns: for, says he, “those deep and extensive shades which appear upon the disk of that planet, must be occasioned by the vast seas it contains, which are incapable of reflecting so vivid a light, as the more solid and opaque parts; or by caverns extremely wide and deep, wherein the rays of the sun are absorbed, whence those shades and that obscurity which we call the spots of the moon.” And Zenophanes said, that those immense cavities were inhabited by another race of men, who lived there, just as we do upon earth.

10.  Yet it appears from one place in Plutarch, that in his time, as well as of late, it was disputed by many, whether the moon yielded any exhalations or vapours for the production of rain and the other meteors. He took part with those who held the negative, being persuaded that the moon must be so intensely heated by the never ceasing action of the sun’s rays upon it that all its humidity must be dried up, so as to render it incapable of furnishing new vapours; whence he concludes, that there existed there, neither clouds, nor rains, nor winds; and of course, neither plants nor animals. Now, this is the very reason alleged by such of the moderns as oppose the notion of the moon’s being inhabited; whereas, the only necessary consequence is, that the inhabitants of that planet must be entirely different from those of ours, and by their constitution fitted to such a clime, and such a habitation. But, however this be; it appears from this passage, that the opinion here mentioned, had partizans even in Plutarch’s time, who were no less fertile than we are in conjectures to support it.

Chapter 16 - The Milky Way; Solar Systems, or a Plurality of Worlds

Chapter 16