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

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1example, we ſee them whil'ſt they are alive to fly upwards, a thing
altogether impoſſible for them to do as they are grave bodies;
whereas being dead they can onely fall downwards; and
fore you hold that the reaſons that are of force in all the kinds of
projects above named, cannot take place in birds: Now this is
very true; and becauſe it is ſo, Sagredus, that doth not appear
to be done in thoſe projects, which we ſee the birds to do.
For if

from the top of a Tower you let fall a dead bird and a live one,
the dead bird ſhall do the ſame that a ſtone doth, that is, it ſhall
firſt follow the general motion diurnal, and then the motion of
deſcent, as grave; but if the bird let fall, be a live, what ſhall
hinder it, (there ever remaining in it the diurnal motion) from
ſoaring by help of its wings to what place of the Horizon it ſhall
and this new motion, as being peculiar to the bird, and
not participated by us, muſt of neceſſity be viſible to us; and if
it be moved by help of its wings towards the Weſt, what ſhall
hinder it from returning with a like help of its wings unto the
And, becauſe, in the laſt place, the birds wending its
flight towards the Weſt was no other than a withdrawing from
the diurnal motion, (which hath, ſupppoſe ten degrees of velocity)
one degree onely, there did thereupon remain to the bird whil'ſt
it was in its flight nine degrees of velocity, and ſo ſoon as it did
alight upon the the Earth, the ten common degrees returned to it,
to which, by flying towards the Eaſt it might adde one, and with
thoſe eleven overtake the Tower.
And in ſhort, if we well
ſider, and more narrowly examine the effects of the flight of
birds, they differ from the projects ſhot or thrown to any part of
the World in nothing, ſave onely that the projects are moved by an
external projicient, and the birds by an internal principle.

here for a final proof of the nullity of all the experiments before
alledged, I conceive it now a time and place convenient to
demonſtrate a way how to make an exact trial of them all.
Shut your ſelf up with ſome friend in the grand Cabbin between
the decks of ſome large Ship, and there procure gnats, flies, and
ſuch other ſmall winged creatures: get alſo a great tub (or
other veſſel) full of water, and within it put certain fiſhes; let
alſo a certain bottle be hung up, which drop by drop letteth forth
its water into another bottle placed underneath, having a narrow
neck: and, the Ship lying ſtill, obſerve diligently how thoſe ſmall
winged animals fly with like velocity towards all parts of the
bin; how the fiſhes ſwim indifferently towards all ſides; and how
the diſtilling drops all fall into the bottle placed underneath.
caſting any thing towards your friend, you need not throw it with
more force one way then another, provided the diſtances be equal:
and leaping, as the ſaying is, with your feet cloſed, you will reach

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