Salusbury, Thomas, Mathematical collections and translations (Tome I), 1667

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1in thoſe very great ones which ſundry accidents continually

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
ken, I ſay, by way of ſurpluſſage and Corollary to Simplicius, for

the real truth is, that as concerning theſe ſhots, the ſame ought
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
ments for true, to
thoſe who never
tried them.
Experiments and
arguments againſt
the Earths motion
ſeem ſo far
cluding, as they lie
hid under
SAGR. As for my part I am fully ſatisfied, and very well
derſtand that who ſo ſhall imprint in his fancy this general
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
voke which made the arguments produced ſeem eoncluding.
There yet remains in me ſome hæſitancy (as I have hinted
fore) touching the flight of birds; the which having as it were an
animate faculty of moving at their pleaſure with a thouſand
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
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

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