268An ESSAY
Sides a d and d c of the Figure a b c d.
The
ſame may be demonſtrated of the other Sides;
and therefore the Figures are ſimilar.
ſame may be demonſtrated of the other Sides;
and therefore the Figures are ſimilar.
Now to prove the other Part of the Theorem:
If a perpendicular be ſuppoſed to be let fall from
the Eye upon the Plane of the Figure, and con-
tinued as is neceſſary; it is evident, that O D,
will be to O d, as this Perpendicular, which
meaſures the Diſtance from the Eye to the Plane
of the Figure, is to the Diſtance of the Eye
from the Perſpective Plane, which is meaſur’d
by the Part of the perpendicular, contain’d be-
tween the Eye and the perſpective Plane. Now
this before was manifeſt; viz. that
O D : O d : : A D : a d :
If a perpendicular be ſuppoſed to be let fall from
the Eye upon the Plane of the Figure, and con-
tinued as is neceſſary; it is evident, that O D,
will be to O d, as this Perpendicular, which
meaſures the Diſtance from the Eye to the Plane
of the Figure, is to the Diſtance of the Eye
from the Perſpective Plane, which is meaſur’d
by the Part of the perpendicular, contain’d be-
tween the Eye and the perſpective Plane. Now
this before was manifeſt; viz. that
O D : O d : : A D : a d :
10.
If from a Point in the Geometrical Plane, three
right Lines proceed, which are equal between them-
ſelves, and parallel to the perſpective Plane; the firſt
of which is in the Geometrical Plane, the ſecond ele-
vated Perpendicular to the firſt, and the third in-
clined to it; the Appearances of theſe three right
Lines are equal.
right Lines proceed, which are equal between them-
ſelves, and parallel to the perſpective Plane; the firſt
of which is in the Geometrical Plane, the ſecond ele-
vated Perpendicular to the firſt, and the third in-
clined to it; the Appearances of theſe three right
Lines are equal.