Salusbury, Thomas, Mathematical collections and translations (Tome I), 1667
page |< < of 701 > >|
1the Line A B) is much leſſer than the Line S O, which ſheweth
how
much it mounteth in the Time that the Force opperates along
the
Line B C.
And to meaſure exactly what his Force ought to be in each Point
of
the curved Line A B C D E, it is requiſite to know that it ope­
rates
there juſt in the ſame manner as if it drew the Weight along
a
Plane Circularly Inclined, and that the Inclination of each of the
Points
of this circular Plane were to be meaſured by that of the
right
Line that toucheth the Circle in this Point.
As for example,
when
the Force is at the Point B, for to find the proportion that it
ought
to have with the ponderoſity of the Weight which is at that
time
at the Point G, it is neceſſary to draw the Contingent Line
G
M, and to account that the ponderoſity of the Weight is to the
Force
which is required to draw it along this Plane, and conſe­
quently
to raiſe it, according to the Circle F G H, as the Line G M
is
to SM Again, for as much as B O is triple of O G, the Force
in
B needs to be to the Weight in G but as the third part of the
Line
SM is unto the whole Line G M.
In the ſelf ſame manner,
when
the Force is at the Point D, to know how much the Weight
weigheth
at I, it is neceſſary to draw the Contingent Line betwixt
I
and P, and the right Line I N perpendicular upon the Horizon,
and
from the Point P taken at diſcretion in the Line I P, provided
that
it be below the Point I, you muſt draw P N parallel to the
ſame
Horizon, to the end you may have the proportion that is be­
twixt
the Line I P and the third part of the Line I N, for that which
betwixt
the ponderoſity of the Weight, and the Force that ought to
be
at the Point D for the moving of it: and ſo of others.
Where,
nevertheleſs
, you muſt except the Point H, at which the Contin­
gent
Line being perpendicular upon the Horizon, the Weight can
be
no other than triple the Force which ought to be in C for the
moving
of it: in the Points F and K, at which the Contingent
Line
being parallel unto the Horizon it ſelf, the leaſt Force that
one
can aſſign is ſufficient to move the Weight.
Moreover, that you
may
be perfectly exact, you muſt obſerve that the Lines S G and
P
N ought to be parts of a Circle that have for their Center that
of
the Earth; and GM and I P parts of Spirals drawn between two
ſuch
Circles; and, laſtly, that the right Lines S M and I N both
tending
towards the Center of the Earth are not exactly Paral­
lels
: and furthermore, that the Point H where I ſuppoſe the
Contingent
Line to be perpendicular unto the Horizon ought
to
be ſome ſmall matter nearer to the Point F than to K, at the
which
F and K the Contingent Lines are Parallels unto the ſaid
Horizon
.

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