121
the 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.

CHAP. VII.

Of Wheels, Pins, Leavers, Pullies, their Parts, Sizes and Figures.

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