* Or three parts
of one Rope.
of one Rope.
Of the SCREW.
Amongſt the reſt of Mechanick Inſtruments for ſundry uſes
found out by the Wit of Man, the Screw doth, in my opi
nion, both for Invention and for Utility, hold the firſt
place, as that which is appoſitely accommodated, and ſo contrived
not only to move, but alſo to ſtay and preſs with very great Force,
that taking up but little room, it worketh thoſe effects which other
Inſtruments cannot, unleſs they were reduced to a great Machine.
The Screw therefore being of moſt ingenious and commodious
contrivance, we ought deſervedly to be at ſome pains in explaining,
with all the plainneſs that is poſſible, the Original and Nature of
it. The which that we may do, we will begin at a Speculation,
which, though at firſt bluſh it may appear ſomewhat remote from
the conſideration of this Inſtrument, yet is the Baſis and Founda
tion thereof.
found out by the Wit of Man, the Screw doth, in my opi
nion, both for Invention and for Utility, hold the firſt
place, as that which is appoſitely accommodated, and ſo contrived
not only to move, but alſo to ſtay and preſs with very great Force,
that taking up but little room, it worketh thoſe effects which other
Inſtruments cannot, unleſs they were reduced to a great Machine.
The Screw therefore being of moſt ingenious and commodious
contrivance, we ought deſervedly to be at ſome pains in explaining,
with all the plainneſs that is poſſible, the Original and Nature of
it. The which that we may do, we will begin at a Speculation,
which, though at firſt bluſh it may appear ſomewhat remote from
the conſideration of this Inſtrument, yet is the Baſis and Founda
tion thereof.
No doubt, but that Natures operation in the Motions of Grave
Bodies is ſuch, that any whatever Body that hath a Gravity in it
hath a propenſion of moving, being at liberty, towards the Cen
ter, and that not only ^{*} by the Right Line perpendicularly, but al
ſo (when it cannot do otherwiſe) by any other Line, which ha
ving ſome inclination towards the Center goeth more and more
abaſing. And thus we ſee the Water not only to fall downwards
along the Perpendicular from ſome eminent place, but alſo to run
about the Surface of the Earth along Lines though very little en
clined; as we ſee in the Courſe of Rivers, the Waters of which, if ſo
be that the Bed have any the leaſt declivity, go freely declining
downwards. Which very effect, like as it is diſcerned in all Fluid
Bodies, would appear alſo in hard Bodies, if ſo be, that their Fi
gure and other Accidental and Extern Impediments did not hinder
it. So that we, having a Superficies very well ſmoothed and poli
ſhed, as for inſtance, that of a Looking-glaſs, and a Ball exactly
rotund and ſleek, either of Marble, or of Glaſs, or of any other
Matter apt to be poliſhed, this being placed upon that Superficies
ſhall trundle along, in caſe that this have any, though very ſmall,
inclination; and ſhall lie ſtill only upon that Superficies which is
exactly levelled and parallel to the Plane of the Horizon: as is
that, for example, of a Lake or ſtanding Water being frozen, up
on which the ſaid Spherical Body would ſtand ſtill, but in a con
dition of being moved by every ſmall Force. For we having ſup
poſed that if that Plane did incline but an hairs breadth only, the
ſaid Ball would move along it ſpontaneouſly towards the part de
clining, and on the oppoſite would have a Reſiſtance, nay, would
not be able without ſome Violence to move towards the part
Bodies is ſuch, that any whatever Body that hath a Gravity in it
hath a propenſion of moving, being at liberty, towards the Cen
ter, and that not only ^{*} by the Right Line perpendicularly, but al
ſo (when it cannot do otherwiſe) by any other Line, which ha
ving ſome inclination towards the Center goeth more and more
abaſing. And thus we ſee the Water not only to fall downwards
along the Perpendicular from ſome eminent place, but alſo to run
about the Surface of the Earth along Lines though very little en
clined; as we ſee in the Courſe of Rivers, the Waters of which, if ſo
be that the Bed have any the leaſt declivity, go freely declining
downwards. Which very effect, like as it is diſcerned in all Fluid
Bodies, would appear alſo in hard Bodies, if ſo be, that their Fi
gure and other Accidental and Extern Impediments did not hinder
it. So that we, having a Superficies very well ſmoothed and poli
ſhed, as for inſtance, that of a Looking-glaſs, and a Ball exactly
rotund and ſleek, either of Marble, or of Glaſs, or of any other
Matter apt to be poliſhed, this being placed upon that Superficies
ſhall trundle along, in caſe that this have any, though very ſmall,
inclination; and ſhall lie ſtill only upon that Superficies which is
exactly levelled and parallel to the Plane of the Horizon: as is
that, for example, of a Lake or ſtanding Water being frozen, up
on which the ſaid Spherical Body would ſtand ſtill, but in a con
dition of being moved by every ſmall Force. For we having ſup
poſed that if that Plane did incline but an hairs breadth only, the
ſaid Ball would move along it ſpontaneouſly towards the part de
clining, and on the oppoſite would have a Reſiſtance, nay, would
not be able without ſome Violence to move towards the part