Galilei, Galileo Dialogues on two world systems 1661, tr. Salusbury, Thomas
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21
of natural bodies some are moveable by nature, and others immo­
veable; especially having before defined Nature, to be the prin­
ciple of Motion and Rest.

Finite and termi­
nate circular mo­
tions disorder not
the parts of the
World.

In the circular mo­
tion, every point in
the circumference
is the begining and
end.

Circular motion
onely is uniform.

Circular motion
may be continued
perpetually.

Right motion can­
not naturally be
perpetual.

Right motion as­
signed to natural
bodies, to reduce
them to perfect or­
der, when removed
from their places.

Rest onely, and
circular motion are
apt to conserve or­
der.

SIMPL. Aristotle, though of a very perspicacious wit, would
not strain it further than needed: holding in all his argumen­

tations, that sensible experiments were to be preferred before
any reasons founded upon strength of wit, and said those which
should deny the testimony of sense deserved to be punished with

the loss of that sense; now who is so blind, that sees not the
parts of the Earth and Water to move, as being grave, natural­
ly downwards, namely, towards the centre of the Universe, as­
signed by nature her self for the end and term of right motion
deorsùm; and doth not likewise see the Fire and Air to move
right upwards towards the Concave of the Lunar Orb, as to the
natural end of motion sursùm? And this being so manifestly seen,
and we being certain, that eadem est ratio totius & partium, why
may we not assert it for a true and manifest proposition, that the
natural motion of the Earth is the right motion ad medium, and
that of the Fire, the right à medio?

Sensible experi­
ments are to be pre­
ferred before hu­
mane argument a­
tions.

He who denies
sense, deserves to
be deprived of it.
Sense sheweth that
things grave move
to the medium, and
the light to the
concave.

SALV. The most that you can pretend from this your Dis­
course, were it granted to be true, is that, like as the parts of the
Earth removed from the whole, namely, from the place where
they naturally rest, that is in short reduced to a depraved and dis­
ordered disposure, return to their place spontaneously, and there­
fore naturally in a right motion, (it being granted, that eadem
sit ratio totius & partium) so it may be inferred, that the
Terrestrial Globe removed violently from the place assigned

it by nature, it would return by a right line. This, as I have
said, is the most that can be granted you, and that onely for want
of examination; but he that shall with exactness revise these
things, will first deny, that the parts of the Earth, in returning to
its whole, move in a right line, and not by a circular or mixt; and
really you would have enough to do to demonstrate the contra­
ry, as you shall plainly see in the answers to the particular reasons
and experiments alledged by Ptolomey and Aristotle. Secondly,
If another should say that the parts of the Earth, go not in their
motion towards the Centre of the World, but to unite with its
Whole, and that for that reason they naturally incline towards the
centre of the Terrestrial Globe, by which inclination they con­
spire to form and preserve it, what other All, or what other Centre
would you find for the World, to which the whole Terrene

Globe, being thence removed, would seek to return, that so the
reason of the Whole might be like to that of its parts? It may be
added, That neither Aristotle, nor you can ever prove, that the
Earth de facto is in the centre of the Universe; but if any Centre