Full text: Gravesande, Willem Jacob: An essay on perspective

on PERSPECTIVE. making theſe Abbreviations, will be laid down
in the following Methods.



100. Method II.
70. By the accidental Point of inclin’d Lines.

Thro’ F, the accidental Point of the inclin’d
parallel Lines, draw F H, parallel to the Baſe
Line, and equal to F G. And let A be the
Point, wherein one of the inclin’d Lines meets
the Geometrical Plane.


Fig. 36.

101. Operation .

Aſſume R Q in the Baſe Line, equal to the
inclin’d Line; and draw Lines from the Points
R and Q, to the Point Z, taken at pleaſure in
the Horizontal Plane.

Thro’ a, the Perſpective of A, draw a N pa-
rallel to the Baſe Line; in which aſſume a L,
equal to M N; and draw a Line from the Point
a, to the Point F; and from the Point L, draw
another to the Point H. Then a T will be the
Perſpective ſought.

102. Demonstration .

By the Nature of the accidental Point, the Perſpective ſought is a Part of the Line a F; and therefore, we are only to demonſtrate,
that the Extremity of the faid Perpendicular is in
the Line L H. Which may be thus done.



Let us ſuppoſe a Line, A I, to paſs thro’ the
Point A, parallel to the Baſe Line, and equal to
the inclin’d Line. It is then manifeſt , that L is the Perſpective of I; and conſequently,
L H is the Appearance of a Line paſſing


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