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.
SAGR. Your Diſcourſe hath removed the wonder out of my
mind at two effects, whereof I did not well underſtand the rea­
ſon; One was to ſee, how two, or at the moſt three twines of the

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