An ESSAY
Plane; and at the Points R and S, raiſe the in-

definite perpendiculars R G and S M; and aſſume

the Point M at Pleaſure on S M; from which

raiſe the Perpendicular M N, equal to the given

Line, and draw the Lines M O and N O, cutting

the Line R G in the Points E and G. Then

having drawn a Line at Pleaſure in the per-

ſpective Plane through the Point T, which is

that wherein a Perpendicular falling from the

Eye on the perſpective Plane meets it, aſſume

T H in the ſaid Line, equal to R E, and T I e-

qual to R G; draw the Lines Ta, Ha, through

the Point a, the Perſpective of the Foot of the

given Perpendicular, and through the Point I,

the Line I X, parallel to Ha, and cutting Ta

in X, then a X will be the Appearance ſought.

Fig. 50.

Fig. 41.

It is manifeſt , that the Point T, is the acci-
dental Point of Lines perpendicular to the Geo-

metrical Plane; and conſequently the Per-

ſpective ſought is a Part of T a. Moreover, it

is manifeſt , that if the Feet and Extremities
of two equal right Lines, perpendicular to the

Geometrical Plane be joyn’d by Lines, theſe

Lines of Junction will have parallel Repreſen-

tations; becauſe they are parallel to each other,

as likewiſe to the perſpective Plane. And con-

ſequently, ſince H I, by Conſtruction, is the

Perſpective of a Line perpendicular to the

Geometrical Plane, and equal to the given Line,

and H a paſſes through the Appearances of the

Foot of the ſaid Perpendicular, and the given

Perpendicular; I ſay, that X I, which is paral-

lel to Ha, and paſſes through the Extremity of

the Appeaarance H I, likewiſe paſſes through

the Extremity of the given Line; and there-