Galilei, Galileo Dialogues on two world systems 1661, tr. Salusbury, Thomas
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234
produceth sundry and divers motions in living creatures. And as
to the flexures there is no need of them, the motions being of the
whole, and not of some particular parts; and because they are
to be circular, the meer spherical figure is the most perfect articu­
lation or flection that can be desired.

It is desired to
know, by means of
what flexures and
joynts the Terre­
strial Globe might
move with three
diverse motions.

One only princi­
ple may cause a
plurality of moti­
ons in the Earth.

SIMP. The most that ought to be granted upon this, would be,
that it may hold true in one single motion, but in three different
motions, in my opinion, and that of the Author, it is impossi­
ble; as he going on, prosecuting the objection, writes in the fol­
lowing words. Let us suppose, with Copernicus, that the Earth
moveth of its own faculty, and upon an intrinsick principle from
West to East in the plane of the Ecliptick; and again, that it also
by an intrinsick principle revolveth about its centre, from East to
West; and for a third motion, that it of its own inclination defle­
cteth from North to South, and so back again. It being a conti­
nuate body, and not knit together with joints and flections, our
fancy and our judgment will never be able to comprehend, that
one and the same natural and indistinct principle, that is, that
one and the same propension, should actuate it at the same instant
with different, and as it were of contrary motions. I cannot be­
lieve that any one would say such a thing, unlesse he had under­
took to maintain this position right or wrong.

SALV. Stay a little; and find me out this place in the Book.
Fingamus modo cum Copernico terram aliqua suâ vi, & ab indito
principio impelli ab Occasu ad Ortum in Eclipticæ plano; tum rur­
sus revolvi ab indito etiam principio, circa suimet centrum, ab

Ortu in Occasum; tertio deslecti rursus su opte nutu à septentrio­
ne in Austrum, & vicissim. I had thought, Simplicius, that
that you might have erred in reciting the words of the Au­
thor, but now I see that he, and that very grossely, decei­
veth himself; and to my grief, I find that he hath set himself to
oppose a position, which he hath not well understood; for these
are not the motions which Copernicus assignes to the Earth.
Where doth he find that Copernicus maketh the annual motion
by the Ecliptick contrary to the motion about its own centre? It
must needs be that he never read his Book, which in an hundred
places, and in the very first Chapters affirmeth those motions to
be both towards the same parts, that is from West to East.
But without others telling him, ought he not of himself to com­
prehend, that attributing to the Earth the motions that are ta
ken, one of them from the Sun, and the other from the pri­
mum wobile, they must of necessity both move one and the same
way.

A grosse error
of the opposer of
Copernicus.

A subtil and
withal simple ar­
gument against
Copernicus.

SIMP. Take heed that you do not erre your self, and Coperni­
cus also. The Diurnal motion of the primum mobile, is it not from