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

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1ſtrument: which difficulty is more ſenſible in it than in thoſe afore­
going, foraſmuch as it hath greater Force.
The LEAVER, Vectis.
I Have deferred to ſpeak of the Leaver until the laſt, in regard
that it is of all Engines for raiſing of Weights, the moſt diffi­
cult to be explained.
Let us ſuppoſe that C H is a Leaver, in ſuch manner ſupported
at the point O, (by means of an Iron Pin that paſſeth thorow it
acroſs, or otherwiſe) that it may turn about on this point O, its
part C deſcribing the Semicircle A B C D E, and its part H the
214[Figure 214]
Semicircle F G H I K; and that
the Weight which we would
raiſe by help of it were in H,
and the Force in C, the Line
C O being ſuppoſed triple of
O H.
Then let us conſider that
in the Time whilſt the Force
that moveth this Leaver deſcri­
beth the whole Semicircle
A B C D E, and acteth accord­
ing to the Line A B C D E, al­
though that the Weight deſcri­
beth likewiſe the Semicircle
F G H I K, yet it is not raiſed to
the length of this curved Line
F G H I K, but only to that of the Line F O K; inſomuch that the
Proportion that the Force which moveth this Weight ought to
have to its Ponderoſity ought not to be meaſured by that which is
between the two Diameters of theſe Circles, or between their two
Circumferences, as it hath been ſaid above of the Wheel, but ra­
ther by that which is betwixt the Circumference of the greater,
and the Diameter of the leſſer.
Furthermore let us conſider, that
there is a neceſſity that this Force needeth not to be ſo great, at
ſuch time as it is near to A, or near to E, for the turning of the
Leaver, as then when it is near to B, or to D; nor ſo great when
it is near to B or D, as then when it is near to C: of which the rea­
ſon is, that the Weights do there mount leſs: as it is eaſie to un­
derſtand, if having ſuppoſed that the Line C O H is parallel to the
Horizon, and that A O F cutteth it at Right Angles, we take the
point G equidiſtant from the points F and H, and the point B equi­
diſtant from A and C; and that having drawn G S perpendicular
to F O, we obſerve that the Line F S (which ſheweth how much
the Weight mounteth in the Time that the Force operates along

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