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

on PERSPECTIVE. the Appearance of the Line A E, is a Part of the Line E D. Now, ſince the Point A is in
the two Lines A B, A E; the Appearance of
the ſaid Point will likewiſe be in the Appear-
ances of the aforeſaid two Lines, and conſequent-
ly is in the Point a, the common Section of B V
and E D.

29.1.

16.
Figure 1. Plate 2.
page 16.
Fig. 5.
@ O H F c d E D C G
Figure 2. Fig. 6.
E D O @ c F a b A C B G
Figure 3. Fig. 7.
D F H V C X a I B G E Z A
13.

30. Remarks .

24. If the Diſtance of the Eye be ſo great, that
one of the Points of Diſtance cannot be deno-
ted upon the horizontal Line; another Point, F,
muſt be uſed, diſtant from the Point of Sight
by about one third, or fourth Part of the Di-
ſtance of the Eye. But then, a correſpondent
Part of the Perpendicular A B muſt be likewiſe
taken, and laid off from B to G, in the Baſe
Line.

25. And in this manner may the Repreſentation
of a very diſtant Point be found, if its Diſtance
from the Perſpective Plane be known, together
with the Place wherein a Perpendicular drawn
from that Point cuts the Baſe Line. For, having
firſt drawn a Line, as B V, from the ſaid Point
of Concurrence to the Point of Sight, then B E
muſt be aſſum’d in the Baſe Line; for Example,
equal to the tenth Part of the Diſtance of the
Point whoſe Repreſentation is ſought; and V H
in the Horizontal Line, likewiſe equal to the
tenth Part of the Eye’s Diſtance. Then C, the
Interſection of B V and E H, will be the Appear-
ance ſought.

Note, By this Method may be found the Deep-
nings in Pictures.

The Appearance of the Point A may yet be
otherwiſe found, without drawing the Line B V
from the Point A, in taking B I equal to B A,

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