on PERSPECTIVE.
one of the Directions drawn upon the Geome-
trical Plane; but it is ſufficient here, that the

Angle the ſaid Directions make with the Baſe

Line, be only known: And ſo, as the Problem

expreſſes it, the Geometrical Plane may be en-

tirely laid aſide.

105. When the Perſpective Plane is parallel,

the Sun’s Rays will have no accidental Point; for their Repreſentations are then parallel; in

which Caſe, one of the Parallels muſt be drawn

through the Point a, inſtead of the Line D a. Moreover, when the Perſpective Plane is perpen-

dicular, or inclin’d, and the Sun’s Rays are pa-

rallel thereto; a Line muſt be drawn through the

Point a, parallel to the Baſe Line; as likewiſe

another Line through the Point I, parallel to the

Sun’s Rays; cutting the firſt Line in the Point

ſought.

##
169.
Problem
III.

106. To find the Perſpective of the Shadow of an

elevated Point, when there is ſome Body hindring its

falling upon the Geometrical Plane.

The Perſpective of the Section of the Body

made by a Plane paſſing through the given Point

perpendicular to the Geometrical Plane, and pa-

rallel to the Sun’s Rays, muſt be found: And then

the Interſection of the ſaid Perſpective, and a

Line drawn from the Appearance of the given

Point to the Repreſentation of its Shadow, is the

Repreſentation ſought.