rough double the space.

EXPERIMENT VIII.

Where there are a number of boys, let five or six of them, whose power
of drawing (estimated as in Experiment I) amounts to six times as much
as the force of the boy at the capstan, pull at the end of the rope
which _was_ fastened to the sledge; they will balance the force of the
boy at the capstan: either they, or he, by a sudden pull, may advance,
but if they pull fairly, there will be no advantage on either part. In
this experiment, the rope should pass through the pulley P 3, and
should be coiled round the larger drum. And it must be also observed,
that in all experiments upon the motion of bodies, in which there is
much friction, as where a sledge is employed, the results are never so
uniform as in other circumstances.

_The Pulley._

Upon the pulley we shall say little, as it is in every body's hands,
and experiments may be tried upon it without any particular apparatus.
It should, however, be distinctly inculcated, that the power is not
increased by a fixed pulley. For this purpose, a wheel without a rim,
or, to speak with more propriety, a number of spokes fixed in a nave,
should be employed. (Plate 2. Fig. 9.) Pieces like the heads of
crutches should be fixed at the ends of these spokes, to receive a
piece of girth-web, which is used instead of a cord, because a cord
would be unsteady; and a strap of iron with a hook to it should play
upon the centre, by which it may at times be suspended, and from which
at other times a weight may be hung.

EXPERIMENT IX.

Let the skeleton of a pulley be hung by the iron strap from the
transom of the frame; fasten a piece of web to one of the radii, and
another to the end of the opposite radius. If two boys of equal weight
pull these pieces of girth-web, they will balance each other; or two
equal weights hung to these webs, will be in equilibrio. If a piece
of girth-web be put round the uppermost radius, two equal weights hung
at the ends of it will remain immoveable; but if either of them be
pulled, or if a small additional weight be added to either of them, it
will descend, and the web will apply itself successively to the
ascending radii, and will detach itself from those that are
descending. If this movement be carefully considered, it will be
perceived, that the web, in unfolding itself, acts in the same manner
upon the radii as two ropes would if they were hung to the extremities
of the opposite radii in succession