18993on PERSPECTIVE.
the Eye, and above it, when the ſaid Plane is in-
clined towards the Objects. Obſerve likewiſe,
that F f of Fig. 60. muſt here be aſſumed e-
qual to R S, and the Line Tt, Fig. 61. muſt
be here a Part of the Line Z C continued, and
made equal to R S.
clined towards the Objects. Obſerve likewiſe,
that F f of Fig. 60. muſt here be aſſumed e-
qual to R S, and the Line Tt, Fig. 61. muſt
be here a Part of the Line Z C continued, and
made equal to R S.
III. When the Perſpective Plane is Parallel or
Horizontal.
Horizontal.
Prob. V.
117.
To throw Figures which are in the Geometri-
cal Plane into Perſpective.
cal Plane into Perſpective.
Draw the Line C F at Pleaſure, in which aſ-
11Fig. 63. ſume the Point I, and make I H and I G, equal
to the Eye’s Diſtance from the perſpective
Plane: Moreover, make I C, and I F equal to
the Eye’s Diſtance from the Geometrical Plane,
or at the leaſt, let I G and I H, be to I F and I C,
as the Eye’s Diſtance from the perſpective Plane,
is to its Diſtance from the Geometrical Plane.
This being done, raiſe two Perpendiculars to
the Line C F, in the Points G and H, and take
two Rulers, each of which has two equal Threads
ſo faſten’d to them, that the Diſtance P Q, and
N M be equal: Then about F and C as Centers,
with the Semidiameters M N or P Q, deſcribe
two Arcs cutting the Perpendiculars raiſed at the
Points G and H, in the Points C and D, and fix
the Extremities of the two Threads of one Ruler,
in the Points C and D, and the Threads of the
other, in the Points F and E.
11Fig. 63. ſume the Point I, and make I H and I G, equal
to the Eye’s Diſtance from the perſpective
Plane: Moreover, make I C, and I F equal to
the Eye’s Diſtance from the Geometrical Plane,
or at the leaſt, let I G and I H, be to I F and I C,
as the Eye’s Diſtance from the perſpective Plane,
is to its Diſtance from the Geometrical Plane.
This being done, raiſe two Perpendiculars to
the Line C F, in the Points G and H, and take
two Rulers, each of which has two equal Threads
ſo faſten’d to them, that the Diſtance P Q, and
N M be equal: Then about F and C as Centers,
with the Semidiameters M N or P Q, deſcribe
two Arcs cutting the Perpendiculars raiſed at the
Points G and H, in the Points C and D, and fix
the Extremities of the two Threads of one Ruler,
in the Points C and D, and the Threads of the
other, in the Points F and E.
Operation.
Let Z be the Geometrical Plane, and A a
Point of the given Figures. Move the
Point of the given Figures. Move the
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