16884An ESSAY
Let Z be the Geometrical Plane;
A the Seat
11Fig. 57. of the given Point; and A B the Direction of
the Sun’s Rays.
11Fig. 57. of the given Point; and A B the Direction of
the Sun’s Rays.
Operation.
Draw two right Lines, making a right Angle
with each other; in one of which, aſſume P E,
equal to the Height of the given Point, above
the Geometrical Plane: Then draw the Line
E C thro’ the Point E; making an Angle with
C P, equal to the Sun’s Altitude; and make A B
equal to C P. Find the Appearance of the Point
B; and the Repreſentation ſought, will be
had.
with each other; in one of which, aſſume P E,
equal to the Height of the given Point, above
the Geometrical Plane: Then draw the Line
E C thro’ the Point E; making an Angle with
C P, equal to the Sun’s Altitude; and make A B
equal to C P. Find the Appearance of the Point
B; and the Repreſentation ſought, will be
had.
Note, This Operation, as likewiſe all the
others in this Chapter, regard all the Situations
of the perſpective Plane; and is ſo evident, that
there is no need of demonſtrating it.
others in this Chapter, regard all the Situations
of the perſpective Plane; and is ſo evident, that
there is no need of demonſtrating it.
Proe. II.
104.
To find the Repreſentation of an elevated
Point, whoſe Appearance, as alſo that of its Seat, is
given, without uſing the Geometrical Plane.
Point, whoſe Appearance, as alſo that of its Seat, is
given, without uſing the Geometrical Plane.
Find F, the accidental Point of the 22Fig. 58.
Rays, and D, that of their Direction:
Then
3368, 88,
98. draw a Line from the Point D, through a, the
Perſpective of the Seat of the given Point; and
another from F, through I, the Perſpective of
the given Point: And then b, the Interſection
of the ſaid two Lines, will be the Point ſought;
as is manifeſt.
3368, 88,
98. draw a Line from the Point D, through a, the
Perſpective of the Seat of the given Point; and
another from F, through I, the Perſpective of
the given Point: And then b, the Interſection
of the ſaid two Lines, will be the Point ſought;
as is manifeſt.
Remarks.
order to find the accidental Point of any
ber of inclin’d Lines, we have
ber of inclin’d Lines, we have
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