15274An ESSAY
the Lines themſelves, and T the Accidental Point
oſ Perpendiculars to the Geometrical Plane.
oſ Perpendiculars to the Geometrical Plane.
Operation.
Continue the Line A B until it meets the
Baſe Line in G, and draw the Line G D, which
cut in a and b by Lines drawn from A and B to
the Eye. Then draw the Lines a F and T b In-
terſecting each other in X; and a x will be the
Appearance ſought.
Baſe Line in G, and draw the Line G D, which
cut in a and b by Lines drawn from A and B to
the Eye. Then draw the Lines a F and T b In-
terſecting each other in X; and a x will be the
Appearance ſought.
Demonstration.
Becauſe a b is the Repreſentation of A 1143.
the Appearance of the inclin’d Line is one Part
of a F. But the Extremity of the inclin’d Line
is in a Perpendicular to the Geometrical Plane
raiſed at the Point B; therefore the Repreſen-
tation of the ſaid Extremity is in T b, and con-
ſequently x in the Interſection of this Line and
a F.
of a F. But the Extremity of the inclin’d Line
is in a Perpendicular to the Geometrical Plane
raiſed at the Point B; therefore the Repreſen-
tation of the ſaid Extremity is in T b, and con-
ſequently x in the Interſection of this Line and
a F.
Method III.
91.
Draw F H thro’ the Accidental Point of
the inclin’d Lines, parallel to the Baſe Line,
and equal to o F in Fig. 48. then a is the Perpen-
22Fig. 49. dicular of the Foot of the inclin’d Line whoſe
Perſpective a x may be found as directed n. 70.
the inclin’d Lines, parallel to the Baſe Line,
and equal to o F in Fig. 48. then a is the Perpen-
22Fig. 49. dicular of the Foot of the inclin’d Line whoſe
Perſpective a x may be found as directed n. 70.