on PERSPECTIVE.
being produced, will meet each other in the

Horizontal Line.

##
120.
CHAP. V.

Of throwing Figures into Perſpective, when

the Perſpective Plane is conſider’d as being

inclined.

##
121.
Problem
I.

81. TO find the Perſpective of a Figure in the

Geometrical Plane.

Let X be the Vertical Plane; S I the Station

Line, S the Station Point, and H the Interſecti-

on of the Station Line and Baſe Line. Now

draw the Vertical Line H V through the Point H,

making an Angle with S I, equal to the Angle

of Inclination of the perſpective Plane; then

raiſe the Perpendicular I O to S I, in the Sta-

tion Point S, equal to the Height of the Eye; and through the Extremity of the ſaid Perpen-

dicular, draw the principal Ray O V, paral-

lel to S I, and cutting H V in the Point of

Sight V.

Now it is evident, that O V determines the

Length of the principal Ray, and H V the Di-

ſtance from the Baſe Line to the Horizontal

Line; and ſince the Demonſtration of the

Problems in the aforegoing Chapters regarding

the Geometrical Plane, have alſo Relation to

the perſpective Plane being inclined, the ſaid

Problems may be here uſed; and conſequently,

this inclined perſpective Plane is reduced to a

Perpendicular one, view’d by an Eye, whoſe

Height is H V, and Diſtance O V.