Optica delineatio rectanguli, alterâ parte longioris.
_Latitudo ~BC~ rectanguli ~A~ ponatur in linea plani, adhibito circino,
vel chartulâ complicatâ; & ex punctis ~B~ & ~C~ fiant visuales ad ~O~,
punctum perspectivæ. Tum papyro ex altera parte iterum complicatâ,
notetur longitudo ~CD~ rectanguli; ducendo tum rectam ~DE~ ad punctum
distantiæ, tum rectam ~FG~ parallelam ad ~BC~, quæ complebit opticam
delineationem rectanguli._
_Altera figura ostendit complicationem cruciformem papyri, quæ adhiberi
potest in delineandis rectangulis, seu latitudo eorum sit major
longitudine, aut vice versâ; seu latitudo & longitudo sint æquales._
The Third Figure.
_The Delineation of an Oblong ~Square~ in ~Perspective~._
Let the Breadth BC of the Square A, be plac’d in the Line of the Plan,
by the Compass, or a folded Paper, and from the Points B and C, make the
Visuals to the Point of Sight O. Then fold your Paper cross-wise, and
mark CD the Length of the Square, drawing the Line DE to the Point of
Distance, and the Line FG parallel to BC, which will complete the Optick
Delineation of the oblong Square.
The other Figure shews the Folding of the Paper cross-wise, which is of
ready use in delineating Squares, whose Breadth exceeds their Length, or
_vice versâ_; or whose Length and Breadth are equal.
[Illustration: FIG. IV.]