5525on PERSPECTIVE.
rence with the Geometrical Line;
which would
come to the ſame thing.
come to the ſame thing.
Demonstration.
Firſt continue the Line E a, until it meets
the Horizontal Line in D, and draw a Line
from D to the Eye, and another through the Eye
parallel to the Baſe Line.
the Horizontal Line in D, and draw a Line
from D to the Eye, and another through the Eye
parallel to the Baſe Line.
Then the Parallels O M and F C are at the
ſame Diſtance from each other, as L D is from
E B; whence it follows, that F O is equal to E D,
and therefore O D is parallel to A F. Whence 1113: the Appearance of E A, is a Part of E D. And
after the ſame Manner we prove, that the Re-
preſentation of B A is a Part of B a.
ſame Diſtance from each other, as L D is from
E B; whence it follows, that F O is equal to E D,
and therefore O D is parallel to A F. Whence 1113: the Appearance of E A, is a Part of E D. And
after the ſame Manner we prove, that the Re-
preſentation of B A is a Part of B a.
Remarks.
40.
When there are no Lines drawn, and we
would uſe this Method, the Horizontal Line
may be laid aſide; and then having firſt drawn
the Geometrical Line, whoſe Diſtance from
the Baſe Line is equal to the Length of the Ray,
we aſſume the Diſtance from the Eye to the
Geometrical Line, equal to the Height of the
Eye.
would uſe this Method, the Horizontal Line
may be laid aſide; and then having firſt drawn
the Geometrical Line, whoſe Diſtance from
the Baſe Line is equal to the Length of the Ray,
we aſſume the Diſtance from the Eye to the
Geometrical Line, equal to the Height of the
Eye.
Although this Method appears uſeleſs, as being
more difficult than the precedent ones, yet in
the Eighth Chapter we have ſhewn the Uſe that
may be drawn from it.
more difficult than the precedent ones, yet in
the Eighth Chapter we have ſhewn the Uſe that
may be drawn from it.
Corollary.
41.
It follows from this Demonſtration, that
the Appearances of Lines paſſing through the
Station Point, are all perpendicular to the Baſe
Line; for if the Perpendicular O S be let
the Appearances of Lines paſſing through the
Station Point, are all perpendicular to the Baſe
Line; for if the Perpendicular O S be let