Salusbury, Thomas Mathematical collections and translations 1667
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117

SIMPL. It may, in case the Ship were incorruptible, but the
Ship decaying, the Navigation must of necessity come to an end.

SALV. But in the Mediterrane, though the Vessel were incor­
ruptible, yet could she not sail perpetually towards Palestina, that

Voyage being determined. Two things then are required, to the
end a moveable may without intermission move perpetually; the
one is, that the motion may of its own nature be indeterminate and
infinite; the other, that the moveable be likewise incorruptible
and eternal.

Two things re­
quisite to the end a
motion may per­
petuate it self; an
unlimited space,
and an incorrupti­
ble moveable.

SIMPL. All this is necessary.

SALV. Therefore you may see how of your own accord you
have confessed it impossible that any moveable should move eter­
nally in a right line, in regard that right motion, whether it be up­

wards, or downwards, is by you your self bounded by the circum­
ference and centre; so that if a Moveable, as suppose the Earth
be eternal, yet forasmuch as the right motion is not of its own na­
ture eternall, but most ^{*}terminate, it cannot naturally suit with

the Earth. Nay, as was said ^{*} yesterday, Aristotle himself is

constrained to make the Terrestrial Globe eternally immoveable.
When again you say, that the parts of the Earth evermore move
downwards, all impediments being removed, you egregiously equi­
vocate; for then, on the other side they must be impeded, contra­
ried, and forced, if you would have them move; for, when they
are once fallen to the ground, they must be violently thrown up­
wards, that they may a second time fall; and as to the impedi­
ments, these only hinder its arrival at the centre; but if there were
a Well, that did passe thorow and beyond the centre, yet would not
a clod of Earth passe beyond it, unlesse inasmuch as being trans­
ported by its impetus, it should passe the same to return thither a­
gain, and in the end there to rest. As therefore to the defending,
that the motion by a right line doth or can agree naturally neither
to the Earth, nor to any other moveable, whil'st the Universe re­
taineth its perfect order, I would have you take no further paines a­
bout it, but (unlesse you will grant them the circular motion)
your best way will be to defend and maintain their immobility.

Right motion
cannot be eternal,
and consequently
cannot be natural
to the Earth.

* Terminatissimo.

* By this expressi­
on he every where
means the prece­
ding Dialogue, or
Giornata.

SIMPL. As to their immoveablenesse, the arguments of Ari­
stotle, and moreover those alledged by your self seem in my opini­
on necessarily to conclude the same, as yet; and I conceive it will
be a hard matter to refute them.

SALV. Come we therefore to the second Argument, which was,
That those bodies, which we are assured do move circularly, have

more than one motion, unlesse it be the Primum Mobile; and
therefore, if the Earth did move circularly, it ought to have two
motions; from which alterations would follow in the rising and
setting of the Fixed Stars: Which effect is not perceived to ensue.