1the Plain upon which it is to be drawn, which
is what we are here to conſider, may be effect
ed in the following Manner. Let ſuch a Num
ber of Poles be laid along, and of ſuch a
Strength and Thickneſs as may be ſufficient
for the Weight; let them be ſound, even,
ſmooth, and cloſe joined to one another: Be
tween the Bottom of the Weight and this Plain
which it is to ſlide upon, there ſhould be ſome
thing to make the Way more ſlippery; and
this may be either Soap, or Tallow, or Lees of
Oil, or perhaps Slime. There is another Way
of making the Weight ſlip along, which is by
underlaying it croſs-ways with Rollers: But
theſe, though you have a ſufficient Number of
them, are very hard to be kept even to their
proper Lines and exact Direction; which it is
abſolutely neceſſary they ſhould be, and that
they ſhould all do Duty equally and at once,
or elſe they will run together in Confuſion,
and carry the Weight to one Side And if you
have but few of them, being continually load
ed, they will either be ſplit or flatted, and ſo
be rendered uſeleſs; or elſe that ſingle Line
with which they touch the Plain underneath,
or that other with which they touch the
Weight that is laid upon them, will ſtick faſt
with their ſharp Points and be immoveable
A Cylinder or Roller is a Body conſiſting of a
Number of Circles joined together; and the
Mathematicians ſay that a Circle can never
touch a right Line in more than one Point;
for which Reaſon I call the ſingle Line which
is preſſed by the Weight, the Point of the Rol
ler. The only Way to provide againſt this In
convenience, is to have the Roller made of the
ſtrongeſt and ſoundeſt Stuff, and exactly ac
cording to Rule and Proportion.
is what we are here to conſider, may be effect
ed in the following Manner. Let ſuch a Num
ber of Poles be laid along, and of ſuch a
Strength and Thickneſs as may be ſufficient
for the Weight; let them be ſound, even,
ſmooth, and cloſe joined to one another: Be
tween the Bottom of the Weight and this Plain
which it is to ſlide upon, there ſhould be ſome
thing to make the Way more ſlippery; and
this may be either Soap, or Tallow, or Lees of
Oil, or perhaps Slime. There is another Way
of making the Weight ſlip along, which is by
underlaying it croſs-ways with Rollers: But
theſe, though you have a ſufficient Number of
them, are very hard to be kept even to their
proper Lines and exact Direction; which it is
abſolutely neceſſary they ſhould be, and that
they ſhould all do Duty equally and at once,
or elſe they will run together in Confuſion,
and carry the Weight to one Side And if you
have but few of them, being continually load
ed, they will either be ſplit or flatted, and ſo
be rendered uſeleſs; or elſe that ſingle Line
with which they touch the Plain underneath,
or that other with which they touch the
Weight that is laid upon them, will ſtick faſt
with their ſharp Points and be immoveable
A Cylinder or Roller is a Body conſiſting of a
Number of Circles joined together; and the
Mathematicians ſay that a Circle can never
touch a right Line in more than one Point;
for which Reaſon I call the ſingle Line which
is preſſed by the Weight, the Point of the Rol
ler. The only Way to provide againſt this In
convenience, is to have the Roller made of the
ſtrongeſt and ſoundeſt Stuff, and exactly ac
cording to Rule and Proportion.
CHAP. VII.
But as there are ſeveral other Things, be
ſides thoſe already mentioned, which are
neceſſary for our Purpoſe, ſuch as Wheels, Pul
lies, Skrews and Leavers, we ſhall here treat of
them more diſtinctly. Wheels in a great Mea
ſure are the ſame as Rollers, as they always
preſs down perpendicularly upon one Point:
But there is this Difference between them,
namely, that Rollers are more expeditious,
Wheels being hindered by the Friction of their
Pins or Axis. The Parts of a Wheel are three:
The large outer Circle, the Pin or Axis in the
Middle, and the Hole or Circle into which the
Pin is let. This Circle ſome perhaps would
rather call the Pole; but becauſe in ſome Ma
chines it ſtands ſtill, and in others moves about,
we rather deſire Leave to call it the Axicle.
If the Wheel turns upon a very thick Axis, it
will go very hard; if upon too thin a one, it
will not ſupport its Load; if the outer Circle
of the Wheel be too ſmall, the ſame Inconve
nience will happen that we obſerved of the
Roller, that is, it will ſtick in the Plain; if it
be too large, it will go along tottering from
Side to Side, and it will never be ready or
handy at turning one way or the other. If the
Axicle or Circle in which the Axis turns, be
too large, it will grind its Way out; if it be
too narrow, it will hardly be able to turn. Be
tween the Axis and the Circle in which it turns,
there ſhould be ſomewhat to lubricate: Be
cauſe one of theſe is to be conſidered as the
Plain, and the other as the Bottom or Keel of
the Weights. Rollers and Wheels ſhould be
made of Elm or Holm-Oak: The Axis of
Holly or the Cornel-tree, or indeed rather of
Iron: The Circle for the Wheel to turn in, is
made beſt of Braſs with one third of Tin. Pul
lies are little Wheels. Leavers are of the Na
ture of the Radii or Spokes of a Wheel. But
every Thing of this Sort, whether large Wheels
which Men turn about by walking within
them, or Cranes or Skrews, or any other En
gine, working either by Leavers or Pullies; the
Principles, I ſay, of all theſe are deduced from
the Balance. They tell us, that Mercury was
believed to be a God chiefly upon this Ac
count, that without the leaſt Geſture with his
Hand, he could make his Meaning perfectly
clear and plain by his Words. This, though
I am a little fearful of ſucceeding in it, I ſhall
here endeavour to do to the utmoſt of my
Power: For my Deſign is to ſpeak of theſe
Things not like a Mathematician, but like a
Workman; and to ſay no more than is abſo
lutely neceſſary. For the clearer underſtand
ing therefore of this Matter, I will ſuppoſe that
you have in your Hand, a Dart. In this Dart I
ſides thoſe already mentioned, which are
neceſſary for our Purpoſe, ſuch as Wheels, Pul
lies, Skrews and Leavers, we ſhall here treat of
them more diſtinctly. Wheels in a great Mea
ſure are the ſame as Rollers, as they always
preſs down perpendicularly upon one Point:
But there is this Difference between them,
namely, that Rollers are more expeditious,
Wheels being hindered by the Friction of their
Pins or Axis. The Parts of a Wheel are three:
The large outer Circle, the Pin or Axis in the
Middle, and the Hole or Circle into which the
Pin is let. This Circle ſome perhaps would
rather call the Pole; but becauſe in ſome Ma
chines it ſtands ſtill, and in others moves about,
we rather deſire Leave to call it the Axicle.
If the Wheel turns upon a very thick Axis, it
will go very hard; if upon too thin a one, it
will not ſupport its Load; if the outer Circle
of the Wheel be too ſmall, the ſame Inconve
nience will happen that we obſerved of the
Roller, that is, it will ſtick in the Plain; if it
be too large, it will go along tottering from
Side to Side, and it will never be ready or
handy at turning one way or the other. If the
Axicle or Circle in which the Axis turns, be
too large, it will grind its Way out; if it be
too narrow, it will hardly be able to turn. Be
tween the Axis and the Circle in which it turns,
there ſhould be ſomewhat to lubricate: Be
cauſe one of theſe is to be conſidered as the
Plain, and the other as the Bottom or Keel of
the Weights. Rollers and Wheels ſhould be
made of Elm or Holm-Oak: The Axis of
Holly or the Cornel-tree, or indeed rather of
Iron: The Circle for the Wheel to turn in, is
made beſt of Braſs with one third of Tin. Pul
lies are little Wheels. Leavers are of the Na
ture of the Radii or Spokes of a Wheel. But
every Thing of this Sort, whether large Wheels
which Men turn about by walking within
them, or Cranes or Skrews, or any other En
gine, working either by Leavers or Pullies; the
Principles, I ſay, of all theſe are deduced from
the Balance. They tell us, that Mercury was
believed to be a God chiefly upon this Ac
count, that without the leaſt Geſture with his
Hand, he could make his Meaning perfectly
clear and plain by his Words. This, though
I am a little fearful of ſucceeding in it, I ſhall
here endeavour to do to the utmoſt of my
Power: For my Deſign is to ſpeak of theſe
Things not like a Mathematician, but like a
Workman; and to ſay no more than is abſo
lutely neceſſary. For the clearer underſtand
ing therefore of this Matter, I will ſuppoſe that
you have in your Hand, a Dart. In this Dart I