Salusbury, Thomas, Mathematical collections and translations (Tome I), 1667

#### Table of figures

< >
[Figure 191]
[Figure 192]
[Figure 193]
[Figure 194]
[Figure 195]
[Figure 196]
[Figure 197]
[Figure 198]
[Figure 199]
[Figure 200]
[Figure 201]
[Figure 202]
[Figure 203]
[Figure 204]
[Figure 205]
[Figure 206]
[Figure 207]
[Figure 208]
[Figure 209]
[Figure 210]
[Figure 211]
[Figure 212]
[Figure 213]
[Figure 214]
[Figure 215]
[Figure 216]
[Figure 217]
[Figure 218]
[Figure 219]
[Figure 220]
< >
page |< < of 701 > >|
1raiſeth it, and cannot be eſtimated ſave wthin a ſmall matter.
Moreover, it is neceſſary to obſerve, that it is nothing but the
redoubling of the Chord, and not the Pulley, that cauſeth this
Force: for if we faſten yet another Pulley towards A, about
which we paſs the Chord A B C H, there will be required no leſs
Force to draw H towards K, and ſo to lift up the Weight E, than
there was before to draw C towards G.
But if to theſe two Pul­
leys we add yet another towards D, to which we faſten the Weight,
and in which we make the Chord to run or ſlip, juſt as we did in
the firſt, then we ſhall need no more Force to lift up this Weight
of 200 pounds than to lift up 50 pounds without the Pulley: be­
cauſe that in drawing four feet of Chord we lift it up but one
foot.
And ſo in multiplying of the Pulleys one may raiſe the great­
eſt Weights with the leaſt Forces.
It is requiſite alſo to obſerve,
that a little more Force is alwaies neceſſary for the raiſing of a
Weight than for the ſuſtaining of it: which is the reaſon why I
have ſpoken here diſtinctly of the one and of the other.
The Inclined PLANE.
If not having more Force than ſufficeth to raiſe 100 pounds, one
would nevertheleſs raiſe this Body F, that weigheth 200 pounds,
to the height of the Line B A, there needs no more but to draw
or rowl it along the Inclined Plane C A, which I ſuppoſe to be
twice as long as the Line

A B, for by this means,
for to make it arrive at
the point A, we muſt
there employ the Force
that is neceſſary for the
raiſing 100 pounds twice
as high, and the more inclined this Plane ſhall be made, ſo much
the leſs Force ſhall there need to raiſe the Weight F.
But yet there
is to be rebated from this Calculation the difficulty that there is
in moving the Body F, along the Plane A C, if that Plane were
laid down upon the Line B C, all the parts of which I ſuppoſe to
be equidiſtant from the Center of the Earth.
It is true, that this impediment being ſo much leſs as the Plane is
more united, more hard, more even, and more polite; it cannot
likewiſe be eſtimated but by gueſs, and it is not very conſide­
rable.
We need not neither much to regard that the Line B C being a
part of a Circle that hath the ſame Center with the Earth, the
Plane A C ought to be (though but very little) curved, and to
have the Figure of part of a Spiral, deſcribed between two Circles,