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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
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