Salusbury, Thomas Mathematical collections and translations 1667

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162
in those very great ones which sundry accidents continually pro­

duce. And all this hath been spoken and granted on good grounds
to Simplicius, and only with an intent to advertise him how much
it importeth to be cautious in granting many experiments for true
to those who never had tried them, but only eagerly alledged them
just as they ought to be for the serving their purpose: This is spo­
ken, I say, by way of surplussage and Corollary to Simplicius, for

the real truth is, that as concerning these shots, the same ought ex­
actly to befall aswell in the motion as in the rest of the Terrestrial
Globe; as likewise it will happen in all the other experiments
that either have been or can be produced, which have at first blush
so mnch semblance of truth, as the antiquated opinion of the
Earths motion hath of equivocation.

It is requisite to
be very cautious in
admitting experi­
ments for true, to
those who never
tried them.

Experiments and
arguments against
the Earths motion
seem so far con­
cluding, as they lie
hid under equi­
vokes.

SAGR. As for my part I am fully satisfied, and very well un­
derstand that who so shall imprint in his fancy this general com­
munity of the diurnal conversion amongst all things Terrestrial,
to all which it naturally agreeth, aswell as in the old conceit of its
rest about the centre, shall doubtlesse discern the fallacy and equi­
voke which made the arguments produced seem eoncluding.
There yet remains in me some hæsitancy (as I have hinted be­
fore) touching the flight of birds; the which having as it were an
animate faculty of moving at their pleasure with a thousand mo­
tions, and to stay long in the Air separated from the Earth, and
therein with most irregular windings to go fluttering to and again,
I cannot conceive how amongst so great a confusion of motions,
they should be able to retain the first commune motion; and in
what manner, having once made any stay behind, they can get
it up again, and overtake the same with flying, and kcep pace
with the Towers and trees which hurry with so precipitant a course
towards the East; I say so precipitant, for in the great circle of
the Globe it is little lesse than a thousand miles an hour, whereof
the flight of the swallow I believe makes not fifty.

SALV. If the birds were to keep pace with the course of the
trees by help of their wings, they would os necessity flie very fast;
and if they were deprived of the universal conversion, they would
lag as far behind; and their flight would seem as furious towards
the West, and to him that could discern the same, it would
much exceed the flight of an arrow; but I think we could not be
able to perceive it, no more than we see a Canon bullet, whil'st
driven by the fury of the fire, it flieth through the Air: But the
truth is that the proper motion of birds, I mean of their flight,
hath nothing to do with the universal motion, to which it is nei­
ther an help, nor an hinderance; and that which maintaineth
the said motion unaltered in the birds, is the Air it self, thorough
which they flie, which naturally following the Vertigo of the