|Galilei, Galileo Dialogues on two world systems 1661, tr. Salusbury, Thomas|
I 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 que
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 de
pendent on the gravity, I think that one may confidently, with
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 ne
ver see any motions but such as are composed of the two, circular
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, one
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 de
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 requi
site to know whether it be uniform, or irregular; that is, whe
ther it maintain alwayes one and the same velocity, or else goeth
retarding or accelerating.
SAGR. It is already clear, that it goeth continually accelle