Galilei, Galileo - The systems of the world

Galilei, Galileo, The systems of the world, 1661

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uſe, in the ordinate parts of the World; and we did proceed to
ſay, that it was not ſo in circular motions, of which that which is
made by the moveable in it ſelf, ſtill retains it in the ſame place,

and that which carrieth the moveable by the circumference of a
circle about its fixed centre, neither puts it ſelf, nor thoſe about it
in diſorder; for that ſuch a motion primarily is finite and terminate
(though not yet finiſhed and determined) but there is no point

in the circumference, that is not the firſt and laſt term in the cir
culation; and continuing it in the circumference aſſigned it, it
leaveth all the reſt, within and without that, free for the uſe of
others, without ever impeding or diſordering them. This being
a motion that makes the moveable continually leave, and con

tinually arrive at the end; it alone therefore can primarily be u
niform; for that acceleration of motion is made in the moveable,
when it goeth towards the term, to which it hath inclination;
and the retardation happens by the repugnance that it hath to
leave and part from the ſame term; and becauſe in circular mo
tion, the moveable continually leaves the natural term, and con
tinually moveth towards the ſame, therefore, in it, the repug
nance and inclination are always of equal force: from which e
quality reſults a velocity, neither retarded nor accelerated, i. e. an
uniformity in motion. From this conformity, and from the being

terminate, may follow the perpetual continuation by ſucceſſively
reiterating the circulations; which in an undeterminated line,
and in a motion continually retarded or accelerated, cannot na

turally be. I ſay, naturally; becauſe the right motion which is
retarded, is the violent, which cannot be perpetual; and the ac
celerate arriveth neceſſarily at the term, if one there be; and if
there be none, it cannot be moved to it, becauſe nature moves
not whether it is impoſſible to attain. I conclude therefore, that
the circular motion can onely naturally conſiſt with natural bo
dies, parts of the univerſe, and conſtituted in an excellent diſpo
ſure; and that the right, at the moſt that can be ſaid for it, is

aſſigned by nature to its bodies, and their parts, at ſuch time as
they ſhall be out of their proper places, conſtituted in a depraved
diſpoſition, and for that cauſe needing to be redured by the ſhort
eſt way to their natural ſtate. Hence, me thinks, it may ratio
nally be concluded, that for maintenance of perfect order among ſt
the parts of the World, it is neceſſary to ſay, that moveables are
moveable onely circularly; and if there be any that move not

circularly, theſe of neceſſity are immoveable: there being no
thing but reſt and circular motion apt to the conſervation of or
der. And I do not a little wonder with my ſelf, that Ariſtotle,
who held that the Terreſtrial globe was placed in the centre of
the World, and there remained immoveable, ſhould not ſay, that

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