9443on PERSPECTIVE.
Priſm is greater than the Height of the Eye, the
precedent Method is the ſhorteſt.
precedent Method is the ſhorteſt.
Problem IX.
62.
To throw a Concave Body into Perſpective.
11Fig. 28.
Having firſt ſound the Perſpective of the ſaid
Body, afterwards find the Appearance of its
Cavity, in conſidering the Cavity as a new
Body.
Body, afterwards find the Appearance of its
Cavity, in conſidering the Cavity as a new
Body.
Problem X.
63.
To throw a Sphere into Perſpective.
22Fig. 29.
Let A be the Seat of the Centre of the Sphere;
then the Point I the Perſpective of the Centre
muſt be found, and the Line IV drawn to 3350. Point of Sight V. This being done, raiſe V F per-
pendicular to V I, which make equal to the
Diſtance from the Eye to the perſpective Plane;
and in this Perpendicular continued, take V P
equal to the Diſtance from the Centre of the
Sphere to the perſpective Plane. Through the
Point P draw P Q parallel to V I cutting a Line
drawn from F through I, in Q; and about Q as
a Centre, with the Semidiameter of the Sphere,
draw the Circle C B, to which from the Point F,
draw the Tangents F C and F B, cutting the
Line I V in the Points G and E. On the Line
G E deſcribe the ſemicircle E D T G, wherein
draw the Line G D perpendicular to F I, which
biſect in H, and about H, as a Centre with the Ra-
dius H D, deſcribe the Arc of a Circle, L D R, cut-
ting the Line F I in the Points L and R. Take
the Chord G T in the Semicircle E D T G equal
to R L, and deſcribe a Semicircle T m G upon
G T; in which Semicircle draw ſeveral Lines,
as m n Perpendicular to G T; and cutting
then the Point I the Perſpective of the Centre
muſt be found, and the Line IV drawn to 3350. Point of Sight V. This being done, raiſe V F per-
pendicular to V I, which make equal to the
Diſtance from the Eye to the perſpective Plane;
and in this Perpendicular continued, take V P
equal to the Diſtance from the Centre of the
Sphere to the perſpective Plane. Through the
Point P draw P Q parallel to V I cutting a Line
drawn from F through I, in Q; and about Q as
a Centre, with the Semidiameter of the Sphere,
draw the Circle C B, to which from the Point F,
draw the Tangents F C and F B, cutting the
Line I V in the Points G and E. On the Line
G E deſcribe the ſemicircle E D T G, wherein
draw the Line G D perpendicular to F I, which
biſect in H, and about H, as a Centre with the Ra-
dius H D, deſcribe the Arc of a Circle, L D R, cut-
ting the Line F I in the Points L and R. Take
the Chord G T in the Semicircle E D T G equal
to R L, and deſcribe a Semicircle T m G upon
G T; in which Semicircle draw ſeveral Lines,
as m n Perpendicular to G T; and cutting