ANNOTATION.
Here it is to be noted, that the River it ſelf may have ſundry
and divers heights, in ſeveral parts of its Chanel, by reaſon of
the various velocities of the water, and its meaſures; as hath
been demonſtrated in the firſt book.
and divers heights, in ſeveral parts of its Chanel, by reaſon of
the various velocities of the water, and its meaſures; as hath
been demonſtrated in the firſt book.
SUPPOSITION I.
It is ſuppoſed, that the Rivers equal in breadth, and quick
height, that have the ſame inclination of bed or bottom, ought
alſo to have equal velocities, the accidental impediments being
removed that are diſperſed throughout the courſe of the water,
and abſtracting alſo from the external windes, which may velo
citate, and retard the courſe of the water of the River.
height, that have the ſame inclination of bed or bottom, ought
alſo to have equal velocities, the accidental impediments being
removed that are diſperſed throughout the courſe of the water,
and abſtracting alſo from the external windes, which may velo
citate, and retard the courſe of the water of the River.
SUPPOSITION II.
Let us ſuppoſe alſo, that if there be two Rivers that are in
their beds of equal length, and of the ſame inclination, but of
quick heights unequal, they ought to move with like velocity,
according to the ſenſe explained in the ſecond definition.
their beds of equal length, and of the ſame inclination, but of
quick heights unequal, they ought to move with like velocity,
according to the ſenſe explained in the ſecond definition.
SUPPOSITION III.
Becauſe it will often be requiſite to meaſure the time exactly
in the following Problems, we take that to be an excellent
way to meaſure the time, which was ſhewed me many years ſince
by Signore Galilæo Galilæi, which is as followeth.
in the following Problems, we take that to be an excellent
way to meaſure the time, which was ſhewed me many years ſince
by Signore Galilæo Galilæi, which is as followeth.
A ſtring is to be taken three Roman feet long, to the end of
which a Bullet of Lead is to be hanged, of about two or three
ounces; and holding it by the other end, the Plummet is to be
removed from its perpendicularity a Palm, more or leſs, and then
let go, which will make many ſwings to and again, paſſing and
repaſſing the Perpendicular, before that it ſtay in the ſame: Now
it being required to meaſure the time that is ſpent in any what
ſoever operation, thoſe vibrations are to be numbred, that are
made whilſt the work laſteth; and they ſhall be ſo many ſecond
minutes of an hour, if ſo be, that the ſtring be three Roman feet
long, but in ſhorter ſtrings, the vibrations are more frequent, and
in longer, leſs frequent; and all this ſtill followeth, whether the
Plummet be little or much removed from its Perpendicularity, or
whether the weight of the Lead be greater or leſſer.
which a Bullet of Lead is to be hanged, of about two or three
ounces; and holding it by the other end, the Plummet is to be
removed from its perpendicularity a Palm, more or leſs, and then
let go, which will make many ſwings to and again, paſſing and
repaſſing the Perpendicular, before that it ſtay in the ſame: Now
it being required to meaſure the time that is ſpent in any what
ſoever operation, thoſe vibrations are to be numbred, that are
made whilſt the work laſteth; and they ſhall be ſo many ſecond
minutes of an hour, if ſo be, that the ſtring be three Roman feet
long, but in ſhorter ſtrings, the vibrations are more frequent, and
in longer, leſs frequent; and all this ſtill followeth, whether the
Plummet be little or much removed from its Perpendicularity, or
whether the weight of the Lead be greater or leſſer.
Theſe things being pre-ſuppoſed, we will lay down ſome fa
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