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

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1this place ſpeak of all ſuch as I ſuſpect, which for the moſt part
ariſe onely from this, that men are before-hand over-knowing in
the Mechanicks; that is to ſay, that they are pre-occupied with
Principles that others prove touching theſe matters, which not being
abſolutely true, they deceive the more, the more true they ſeem to
The firſt thing wherewith a man may be pre-occupied in this
buſineſſe, is, that they many times confound the Conſideration of
216[Figure 216]
Space, with that of Time, or of the Ve­
locity, ſo that, for Example, in the
Leaver, or (which is the ſame) the Ba­
llance A B C D having ſuppoſed that
the Arm A B is double to B C, and the
Weight in C double to the Weight
in A, and alſo that they are in Equilibrium, inſtead of ſaying, that
that which cauſeth this Equilibrium is, that if the Weight C did
ſuſtain, or was raiſed up by the Weight A, it did not paſſe more
than half ſo much Space as it, they ſay that it did move ſlower by
the half: which is a fault ſo much the more prejudicial, in that it is
very difficult to be known: for it is not the difference of
217[Figure 217]
the Velocity that is the cauſe why theſe Weights are to be
one double to the other, but the difference of the Space, as
appeareth by this, that to raiſe, for Example, the Weight F
with the hand unto G, it is not neceſſary to employ a Force
that is preciſely double to that which one ſhould have
therein employed the firſt bout, to raiſe it twice as quick­
ly, but it is requiſite to employ therein either more or leſs
than the double, according to the different proportion that
this Velocity may have unto the Cauſes that reſiſt it.
Inſtead of requiring a Force juſt double for the raiſing of it with
the ſame Velocity twice as high, unto H, I ſay that it is juſt dou­
ble in counting (as two and two make four) that one and one make
two, for it is requiſite to employ a certain quantity of this Force
to raiſe the Weight from F to G, and again alſo, as much more of
the ſame Force to raiſe it from G to H.
For if I had had a mind to have joyned the Conſideration of the
Velocity with that of the Space, it had been neceſſary to have
aſſigned three Dimenſions to the Force, whereas I have aſſigned it
no more but two, on purpoſe to exclude it.
And if I have teſtified
that there is ſo little of worth in any part of this ſmall Tract of the
Staticks, yet I de ſire that men ſhould know, that there is more in
this alone than in all the reſt: for it's impoſſible to ſay any thing
that is good and ſolid touching Velocity, without having rightly
explained what we are to underſtand by Gravity, as alſo the whole
Syſteme of the World.
Now becauſe I would not under take it,

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