Salmon, William: Polygraphice: Or, The Arts of Drawing, Engraving, Etching, Limning, Painting, Washing, Varnishing, Gilding, Colouring, Dying, Beautifying and Perfuming: In Four Books ... To which is added A Discourse of Perspective and Chiromancy (London, 1675)

44 Poljgraphices. Lib.t#
VII. In delineating Ovals,Circles, Arches, Crosses*
Spirals and Cross-arches, or any other figure, in the
roof of any room > first draw Ichnographically, and so
with perpendiculars, from the most Eminent points
thereos, carry it up unto the Ceiling, from which seve-
ral points carry on the sigure.
VIII. The center in any Scenographick regular
sigure is found by drawing cross-lines from opposite
angles: for the point where the Diagonals cross is the
Center.
IX. A ground plain of squares is alike, both above
and below the Horizontal line ; only the more it is
distant above or beneath the Horizon, the squares
will be so much the larger or wider.
X. In drawing a perspe£tive figure, where many
lines come together, you may for the directing of your
eye, draw the Diagonals in red ; the visual lines in
black , the Perpendiculars in green, or other different
colour from that which you intend the figure (hall
be of.
XI Having considered the height, distance and
potition of the figure, and drawn it accordingly,
with tide or angle against the base i raise perpendicu-
lars from the several angles or designed points in the
figure, to the base, and transfer the length of each
perpendicular , from the place where it touches the
base, to the base on the side opposite to the point of
distancej so will the Diametrals drawn to the per-
pendiculars in the base, by interstdiion with the Dia-
gonal s drawn to the several transferred distances,give
the angles of the figure : and so lines drawn from
point to point will circumscribe the Scenographick
figure.
XII. If in Landskip there be any landing wa-
ters, as Rivers, Ponds, and the like > place the Ho-
rizontal