Archimedes
,
Natation of bodies
,
1662
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Section of the Portion be A P O L, the Section of a Rightangled
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Cone; and let the Axis of the Portion and Diameter of the Section
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be N O, and the Section of the Surface of the Liquid I S. </
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<
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>If now
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the Portion be not erect, then N O ſhall not be at equall Angles with
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I S. </
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<
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>Draw R
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touching the Section of the Rightangled Conoid
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in P, and parallel to I S: and from the Point P and parall to O N
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draw
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P
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F: and take the Centers of Gravity; and of the Solid A
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P
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O L let the Centre be R; and of that which lyeth within the
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Liquid let the Centre be B; and draw a Line from B to R pro
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longing it to G, that G may be the Centre of Gravity of the Solid
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that is above the Liquid. </
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<
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>And becauſe N O is ſeſquialter of R
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O, and is greater than ſeſquialter of the Semi-Parameter; it is ma
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nifeſt that
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(a)
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R O is greater than the
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Semi-parameter. ^{*}Let therefore R
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H be equall to the Semi-Parameter,
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^{*} and O
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H
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double to H M. </
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<
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>Foraſ
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much therefore as N O is ſeſquialter
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of R O, and M O of O H,
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(b)
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the
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Remainder N M ſhall be ſeſquialter
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of the Remainder R H: Therefore
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the Axis is greater than ſeſquialter
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of the Semi parameter by the quan
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tity of the Line M O. </
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<
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>And let it be
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ſuppoſed that the Portion hath not leſſe proportion in Gravity unto
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the Liquid of equall Maſſe, than the Square that is made of the
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Exceſſe by which the Axis is greater than ſeſquialter of the Semi
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parameter hath to the Square made of the Axis: It is therefore ma
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nifeſt that the Portion hath not leſſe proportion in Gravity to the
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Liquid than the Square of the Line M O hath to the Square of N
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O: But look what proportion the
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P
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ortion hath to the Liquid in
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Gravity, the ſame hath the
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P
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ortion ſubmerged to the whole Solid:
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for this hath been demonſtrated
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(c)
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above: ^{*}And look what pro
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portion the ſubmerged Portion hath to the whole
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P
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ortion, the
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ſame hath the Square of
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P
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F unto the Square of N O: For it hath
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been demonſtrated in
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(d) Lib. de Conoidibus,
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that if from a Right
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angled Conoid two
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P
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ortions be cut by Planes in any faſhion pro
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duced, theſe
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P
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ortions ſhall have the ſame Proportion to each
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other as the Squares of their Axes: The Square of P F, therefore,
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hath not leſſe proportion to the Square of N O than the Square of
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M O hath to the Square of N O: ^{*}Wherefore P F is not leſſe than
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M O, ^{*}nor B P than H O. ^{*}If therefore, a Right Line be drawn
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from H at Right Angles unto N O, it ſhall meet with B
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P,
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and ſhall
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fall betwixt B and P; let it fall in T:
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(e)
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And becauſe
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P
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F is
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parallel to the Diameter, and H T is perpendicular unto the ſame
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Diameter, and R H equall to the Semi-parameter; a Line drawn
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from R to T and prolonged, maketh Right Angles with the Line </
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