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

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1I will not conſent that our Poem ſhould be ſo confined to that
unity, as not to leave us fields open for Epſody's, which every
ſmall connection ſhould ſuffice to introduce; but with almoſt as
much liberry as if we were met to tell ſtories, it ſhall be lawful
for me to ſpeak, what ever your diſcourſe brings into my mind.
SAGR. I like this motion very well; and ſince we are at this
liberty, let me take leave, before we paſſe any farther to ask of
you Salviatus, whether you did ever conſider what that line may
be that is deſcribed by the grave moveable naturally falling down
from the top of a Tower; and if you have reflected on it, be
pleaſed to tell me what you think thereof.
SALV. I have ſometimes conſidered of it, and make no
ſtion, that if one could be certain of the nature of that motion
wherewith the grave body deſcendeth to approach the centre of
the Terreſtrial Globe, mixing it ſelf afterwards with the common
circular motion of the diurnal converſion; it might be exactly
found what kind of line that is, that the centre of gravity of the
moveable deſcribeth in thoſe two motions.
SAGR. Touching the ſimple motion towards the centre
pendent on the gravity, I think that one may confidently,
out error, believe that it is by a right line, as it would be, were
the Earth immoveable.
SALV. As to this particular, we may not onely believe it, but
experience rendereth us certain of the ſame.
SAGR. But how doth experience aſſure us thereof, if we
ver ſee any motions but ſuch as are compoſed of the two, circular
and deſcending.
SALV. Nay rather Sagredus we onely ſee the ſimple motion of
deſcent; ſince that other circular one common to the Earth, the
Tower and our ſelves remains imperceptible, and as if it never
were, and there remaineth perceptible to us that of the ſtone,
ly not participated by us, and for this, ſenſe demonſtrateth that
it is by a right line, ever parallel to the ſaid Tower, which is
built upright and perpendicular upon the Terreſtrial ſurface.
SAGR. You are in the right; and this was but too plainly
monſtrated to me even now, ſeeing that I could not remember ſo
eaſie a thing; but this being ſo manifeſt, what more is it that you
ſay you deſire, for underſtanding the nature of this motion
SALV. It ſufficeth not to know that it is ſtreight, but its
ſite to know whether it be uniform, or irregular; that is,
ther it maintain alwayes one and the ſame velocity, or elſe goeth
retarding or accelerating.
SAGR. It is already clear, that it goeth continually

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