From the Inſtrument laſt deſcribed, the other Inſtrument which
we call the Crane is not much different, as to form, nay, differeth
nothing, ſave in the way of applying or employing it: For that the
Capſten moveth and is conſtituted perpendicular to the Horizon,
and the Crane worketh with its Moment parallel to the ſame Ho
187[Figure 187]
rizon. For if upon the Circle D A E we ſuppoſe an Axis to be
placed Column-wiſe, turning about the Center B, and about which
the Rope D H, faſtened to the Weight that is to be drawn, is be
laid, and if the Bar F E B D be let into the ſaid Axis [by the Mor
tace B] and the Force of a Man, of an Horſe, or of ſome other
Animal apt to draw, be applyed at its end F, which moving round,
paſſeth along the Circumference F G C, the Crane ſhall be framed
and finiſhed, ſo that by carrying round the Bar F B D, the Barrell
or Axis E A D ſhall turn about, and the Rope which is twined a
bout it, ſhall conſtrain the Weight H to go forward: And becauſe
the point of the Fulciment about which the Motion is made, is the
point B, and the Moment keeps at a Diſtance from it according to
the Line B F, and the Reſiſtor at the Diſtance B D, the Leaver
F B D is formed, by vertue of which the Force acquireth Moment
equall to the Reſiſtance, if ſo be, that it be in proportion to it, as
the Line B D is to B F, that is, as the Semidiameter of the Axis to
the Semidiameter of the Circle, along whoſe Circumference the
Force moveth. And both in this, and in the other Inſtrument we
are to obſerve that which hath been frequently mentioned, that is,
That the benefit which is derived from theſe Machines, is not that
which the generality of the Vulgar promiſe themſelves from the
Mechanicks; namely, that being too hard for Nature, its poſſible
we call the Crane is not much different, as to form, nay, differeth
nothing, ſave in the way of applying or employing it: For that the
Capſten moveth and is conſtituted perpendicular to the Horizon,
and the Crane worketh with its Moment parallel to the ſame Ho
187[Figure 187]rizon. For if upon the Circle D A E we ſuppoſe an Axis to be
placed Column-wiſe, turning about the Center B, and about which
the Rope D H, faſtened to the Weight that is to be drawn, is be
laid, and if the Bar F E B D be let into the ſaid Axis [by the Mor
tace B] and the Force of a Man, of an Horſe, or of ſome other
Animal apt to draw, be applyed at its end F, which moving round,
paſſeth along the Circumference F G C, the Crane ſhall be framed
and finiſhed, ſo that by carrying round the Bar F B D, the Barrell
or Axis E A D ſhall turn about, and the Rope which is twined a
bout it, ſhall conſtrain the Weight H to go forward: And becauſe
the point of the Fulciment about which the Motion is made, is the
point B, and the Moment keeps at a Diſtance from it according to
the Line B F, and the Reſiſtor at the Diſtance B D, the Leaver
F B D is formed, by vertue of which the Force acquireth Moment
equall to the Reſiſtance, if ſo be, that it be in proportion to it, as
the Line B D is to B F, that is, as the Semidiameter of the Axis to
the Semidiameter of the Circle, along whoſe Circumference the
Force moveth. And both in this, and in the other Inſtrument we
are to obſerve that which hath been frequently mentioned, that is,
That the benefit which is derived from theſe Machines, is not that
which the generality of the Vulgar promiſe themſelves from the
Mechanicks; namely, that being too hard for Nature, its poſſible
zoom in
zoom out
zoom area
full page
page width
set mark
remove mark
get reference
digilib