another earth, which we see to turn round its centre? Is not Venus
another earth, where we observe the same phenomenon? Are not the
revolutions of the sun also a confirmation, from analogy, of the same
theory? All the planets, are they not earths, which revolve about the
sun? Are not the satellites moons, which move round Jupiter and Saturn,
and along with these primary planets round the sun? These analogies and
resemblances, with others which I have not mentioned, are the sole proofs
of the COPERNICAN system; and to you it belongs to consider, whether you
have any analogies of the same kind to support your theory.

In reality, CLEANTHES, continued he, the modern system of astronomy is
now so much received by all inquirers, and has become so essential a part
even of our earliest education, that we are not commonly very scrupulous
in examining the reasons upon which it is founded. It is now become a
matter of mere curiosity to study the first writers on that subject, who
had the full force of prejudice to encounter, and were obliged to turn
their arguments on every side in order to render them popular and
convincing. But if we peruse GALILEO's famous Dialogues concerning the
system of the world, we shall find, that that great genius, one of the
sublimest that ever existed, first bent all his endeavours to prove, that
there was no foundation for the distinction commonly made between
elementary and celestial substances. The schools, proceeding from the
illusions of sense, had carried this distinction very far; and had
established the latter substances to be ingenerable, incorruptible,
unalterable, impassable; and had assigned all the opposite qualities to
the former. But GALILEO, beginning with the moon, proved its similarity
in every particular to the earth; its convex figure, its natural darkness
when not illuminated, its density, its distinction into solid and liquid,
the variations of its phases, the mutual illuminations of the earth and
moon, their mutual eclipses, the inequalities of the lunar surface, &c.