Galilei, Galileo Dialogues on two world systems 1661, tr. Salusbury, Thomas
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104
would never with his walking have arrived, if the Ship with its
motion had not wafted him thither.

A single move­
able hath but onely
one natural moti­
on, and all the
rest are by partici­
pation.

SAGR. Tell me secondly. That motion, which is communi­
cated to any moveable by participation, whilest it moveth by it
self, with another motion different from the participated, is it
necessary, that it do reside in some certain subject by it self, or
else can it subsist in nature alone, without other support.

SIMPL. Aristotle giveth you an answer to all these questions,

and tels you, that as of one sole moveable the motion is but one;
so of one sole motion the moveable is but one; and consequent­
ly, that without the inherence in its subject, no motion can ei­
ther subsist, or be imagined.

Motion cannot
be made without
its moveable sub­
ject.

SAGR. I would have you tell me in the third place, whether
you beblieve that the Moon and the other Planets and Cœlestial
bodies, have their proper motions, and what they are.

SIMPL. They have so, and they be those according to which
they run through the Zodiack, the Moon in a Moneth, the Sun
in a Year, Mars in two, the Starry Sphere in those so many thou­
sand. And these are their proper, or natural motions.

SAGR. But that motion wherewith I see the fixed Stars, and
with them all the Planets go unitedly from East to West, and re­
turn round to the East again in twenty four hours, how doth it
agree with them?

SIMPL. It suiteth with them by participation.

SAGR. This then resides not in them, and not residing in
them, nor being able to subsist without some subject in which it
is resident, it must of force be the proper and natural motion of
some other Sphere.

SIMPL. For this purpose Astronomers, and Philosophers have
found another high Sphere, above all the rest, without Stars, to
which Natural agreeth the Diurnal Motion; and this they call
the Primum mobile; the which carrieth along with it all the in­
feriour Spheres, contributing and imparting its motion to
them.

SAGR. But when, without introducing other Spheres unknown
and hugely vast, without other motions or communicated raptures,
with leaving to each Sphere its sole and simple motion, without
intermixing contrary motions, but making all turn one way, as
it is necessary that they do, depending all upon one sole principle,
all things proceed orderly, and correspond with most perfect har­
mony, why do we reject this Phœnomenon, and give our assent to
those prodigious and laborious conditions?

SIMPL. The difficulty lyeth in finding out this so natural and
expeditious way.