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

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1fingers, did not yield to follow him that would have forceably
drawn
it from between them, reſiſted, becauſe it was ſtayed by a
double
compreſſion, ſince the upper finger preſt no leſſe againſt
the
nether, than it preſſed againſt that.
And there is no queſtion,
that
if of theſe two preſſures, one alone might be retained, there
would
remain half of that Reſiſtance, which depended conjunctive­
ly
on them both: but becauſe you cannot with removing, v.g. the
upper
finger take away its preſſion, without taking away the other
part
alſo; it will be neceſſary by ſome new Artifice to retain one
of
them, and to find a way that the ſame thread may compreſſe it
ſelf
againſt the finger or other ſolid body upon which it is put; and
this
is done by winding the ſame thread about the Solid.
For the
better
underſtanding whereof, I will briefly give it you in Figure;
and
let A B and CD be two Cilinders, and between them let there
be
diſtended the thread E F, which for greater plainneſſe I will
repreſent
to be a ſmall Cord: there is no doubt but that the two
Cylinders
being preſſed hard one againſt the other, the Cord
E F pulled by the end F will Reſiſt no ſmal force before
it
will ſlip from between the two Solids compreſſing it: but if
we
remove one of them, though the Cord
53[Figure 53]
continue
touching the other, yet ſhall it not
by
ſuch contact be hindered from ſlipping
away
.
But if holding it faſt, though but
gently
in the point A, towards the top of the
Cylinder
, we wind, or belay it about the
ſame
ſpirally in A F L O T R, and pull it by
the
end R: it is manifeſt, that it will begin
to
preſſe the Cylinder, and if the windings
and
wreathes be many, it ſhall in its effectual
drawing
alwaies preſſe it ſo much the ſtrai­
ter
about the Cylinder: and by multiplying
the
wreathes if you make the contact longer,
and
conſequently more invincible, the more
difficult
ſtill ſhall it be to withdraw the
Cord
, and make it yield to the force that
pulls
it.
Now who ſeeth not, that the ſame
Reſiſtance
is in the threads, which with many thouſand ſuch
twinings
ſpin the thick Cord?
Yea, the ſtreſſe of ſuch twiſting
bindeth
with ſuch Tenacity, that a few Ruſhes, and of no great
length
, (ſo that the wreaths and windings are but few where­
with
they entertwine) make very ſtrong bands, called, as I take it,

^
{*} Thum-ropes.
* Fuſta.

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