_A Pedestal in Perspective._
Here also, after you have made the two foregoing Preparations, the
Geometrical and the Perspective; this shadow’d Pedestal is made by
taking with the Compasses the Angles of the Plan, for drawing the
Perpendiculars, and the Angles of the Profile for the level Lines, as
before. Thus the two Angles of the Plan MO, give the perpendicular Lines
EF. The Angle of the Plan R, gives the Perpendicular P; and the other
Angles give their respective Perpendiculars. So likewise in the Profile,
the Angle I gives the level Line HN. In short, the first Out-line of
the Profile ID gives the Height of the level Lines on the Front of the
shadow’d Pedestal. The other Out-line Q gives the Height of the occult
and back part thereof.
Nevertheless, two things are to be observ’d; first, that in making the
Geometrical Plan, you draw from the Elevation A, as many Lines to the
Side of the Plan B, as you have Angles in the Projectures of the said
Elevation; as is manifest in the pointed Lines, which fall, from the
Upright A, on the Plan B, where that of the greatest Projecture L in the
Elevation makes the outer Line L of the Plan.
The second thing to be observ’d, is, That if you would have the
Perspective-Plan MOR as far within the Ground-line K, as the Breadth
of the Space C on the same Line, the Space G will then be the Distance
thereof from the said Ground-line.