Gravesande, Willem Jacob 's
,
An essay on perspective
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0174
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An ESSAY
"/>
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<
s
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xml:space
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">Draw the Line e c, equal to the Length of
<
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<
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left
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xlink:label
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note-0174-01
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xlink:href
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note-0174-01a
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xml:space
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preserve
">Fig. 68.</
note
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the Style of the Horizontal Dial; </
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<
s
xml:id
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xml:space
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preserve
">and, at its
<
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two Extremities raiſe the Perpendiculars e o
<
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and c p: </
s
>
<
s
xml:id
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echoid-s2219
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xml:space
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preserve
">Then draw the Line c G, thro’ the
<
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/>
Point c, equal in Length to the Style of the
<
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Dial to be drawn; </
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<
s
xml:id
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echoid-s2220
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xml:space
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">making an Angle with c e,
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equal to the Inclination of the Dial-Plane. </
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<
s
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xml:space
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">Af-
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ter which, draw the Line o G p, thro’ the Ex-
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tremity G of the ſaid Line, perpendicular there-
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to. </
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<
s
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xml:space
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">This Preparation being finiſh’d, we uſe the
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Operations of the precedent Problem, in making
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E O and C P, in the Horizontal Dial, equal to
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e o and c p of this Figure; </
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<
s
xml:id
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xml:space
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">and o p, in the Dial
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to be drawn, equal to op of this Figure; </
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<
s
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xml:space
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">in
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which, the Point G is the Foot of the Style.</
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<
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</
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<
s
xml:id
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xml:space
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">If it happens, in the aforeſaid Preparation,
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<
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xlink:label
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note-0174-02
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xlink:href
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note-0174-02a
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">Fig. 69.</
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that the Line p o cuts the Line e c; </
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<
s
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xml:space
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">E O muſt
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not then be aſſum’d in the ſame Line, in the
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Horizontal Dial, as otherwiſe it muſt have
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been; </
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<
s
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xml:space
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">but, in that Line, continued on the other
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ſide of the Foot of the Style.</
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<
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<
s
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">The Demonſtration of this Problem, is the
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ſame as that of the precedent one; </
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<
s
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xml:space
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">in conſider-
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ing the Angle p o Q, equal to the Angle G c e,
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which is equal to the Inclination of the Plane.</
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>
<
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<
s
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">We might have further ſhewn the Uſe of
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Perſpective, in facilitating the Operations of
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Dialling: </
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<
s
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">But this would be deviating from our
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Subject; </
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<
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">and ſo we ſhall content our ſelves with
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this Short Eſſay, touching the moſt common and
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uſeful Problem in Dialling.</
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