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

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1Lines, which fall at Right Angles on thoſe whereon the Weights
hang, and would move, if ſo be they were permitted to deſcend
freely.
Of the BALLANCE and LEAVER.
Having underſtood by certain Demonſtration, one of the
firſt Principles, from which, as from a plentiſul Fountain,
many of the Mechanical Inſtruments are derived, we may
take occaſion without any difficulty to come to the knowledge of
the nature of them: and firſt ſpeaking of the Stiliard, an Inſtru­
ment of moſt ordinary uſe, with which divers Merchandizes are
weighed, ſuſtaining them, though very heavy, with a very ſmall
counterpoiſe, which is com­
monly called the Roman or

Plummet, we ſhall prove that
there is no more to be done in
ſuch an operation, but to re­
duce into act and practice
what hath been above contemplated.
For if we propoſe the Bal­
lance A B, whoſe Fulciment or Lanquet is in the point C, by
which, at the ſmall Diſtance C A, hangeth the heavy Weight D,
and if along the other greater C B, (which we call the Needle of
the Stiliard) we ſhould ſuppoſe the Roman F, though of but little
weight in compariſon of the Grave Body D to be ſlipped to and
fro, it ſhall be pofſible to place it ſo remotely from the Lanquet C,
that the ſame proportion may be found between the two Weights
D and F, as is between the Diſtances F C, and C A: and then ſhall
an Equilibrium ſucceed; unequall Weights hanging at Diſtances
alternately proportional to them.
Nor is this Inſtrument different from that other called Vectis,

and vulgarly the ^{*} Leaver, wherewith great Weights are moved
by ſmall Force; the application of which is according to the Fi­
gure prefixed; wherein the Leaver
is repreſented by the Bar of wood
or other ſolid matter, B C D, let

the heavy Weight to be raiſed be
A, and let the ſteadfaſt ſupport
or Fulciment on which the Leaver
reſts and moves be ſuppoſed to be
E, and putting one end of the
Leaver under the Weight A, as
may be ſeen in the point C, en­
creaſing the Weight or Force at the other end D, it will be able
to lift up the Weight A, though not much, whenever the Force in