8941on PERSPECTIVE.
Problem VIII.
59.
To throw a Priſm or Cylinder into Perſpective,
11Fig. 26. both of them being Perpendicular to the Geometri-
cal Plane.
11Fig. 26. both of them being Perpendicular to the Geometri-
cal Plane.
Let G H I L M N be the Baſe of the Priſm
in the Geometrical Plane, and the viſible Part
thereof upon the perſpective Plane, let be n g h i;
then to compleat the Repreſentation of the
Priſm, draw Perpendiculars from the Points
n g h and i to the Baſe Line, whoſe Length let
be ſuch that they may repreſent 2255. lars to the Geometrical Plane, equal to the
Height of the Priſm, and find the 3350. of the other Angular Points of the upper Sur-
face of the Priſm, in confidering them as Points
elevated above the Geometrical Plane: This
being done, if the Repreſentations of all the
ſaid Angular Points be joyn’d, the whole
Priſm will be thrown into Perſpective.
in the Geometrical Plane, and the viſible Part
thereof upon the perſpective Plane, let be n g h i;
then to compleat the Repreſentation of the
Priſm, draw Perpendiculars from the Points
n g h and i to the Baſe Line, whoſe Length let
be ſuch that they may repreſent 2255. lars to the Geometrical Plane, equal to the
Height of the Priſm, and find the 3350. of the other Angular Points of the upper Sur-
face of the Priſm, in confidering them as Points
elevated above the Geometrical Plane: This
being done, if the Repreſentations of all the
ſaid Angular Points be joyn’d, the whole
Priſm will be thrown into Perſpective.
Now to throw a Cylinder into Perſpective,
the Repreſentation of its Baſe and upper Sur-
face muſt firſt be had, by finding the 4450. ance of ſeveral Points of the Periphery of its
upper Surface, and then two Perpendiculars
muſt be ſo drawn to the Baſe Line, that they
may touch the Appearances of the two circular
Euds of the Cylinder, and the Appearance of
the Cylinder will be had. But to avoid uſeleſs
Operations, the viſible Part of the Baſe of the
Cylinder may be thus determin’d. Draw the
Line A S from the Point A to the Station Point S,
then this Line muſt be biſected in the Point R,
about which, as a Centre, and with the Radius
R A, the Circular Arc B A C, muſt be deſcrib’d
cutting the Baſe of the Cylinder in the
the Repreſentation of its Baſe and upper Sur-
face muſt firſt be had, by finding the 4450. ance of ſeveral Points of the Periphery of its
upper Surface, and then two Perpendiculars
muſt be ſo drawn to the Baſe Line, that they
may touch the Appearances of the two circular
Euds of the Cylinder, and the Appearance of
the Cylinder will be had. But to avoid uſeleſs
Operations, the viſible Part of the Baſe of the
Cylinder may be thus determin’d. Draw the
Line A S from the Point A to the Station Point S,
then this Line muſt be biſected in the Point R,
about which, as a Centre, and with the Radius
R A, the Circular Arc B A C, muſt be deſcrib’d
cutting the Baſe of the Cylinder in the