Bowles, Carington [Hrsg.]: All Draughtsmen's Assistant, Or, Drawing Made Easy: Wherein The Principles Of That Art Are Rendered Familiar In Ten Instructive Lessons ... Explain'd by a great Variety of Examples from the most approved Designs, on Copper-plates, neatly engraved: With a suitable Introduction on the Utility of this Noble Art ; And Observations on Design, as well in regard to Theory as Practise (London, [ca. 1777])

( II )

PraBical Examples in P erfp eft he.

To draw a Square Pavement in Perfpective. See Fig. IX. Plate IV.

SUPPOSING you have a Piece of Pavement confiding of 64. Pieces of Marble,
each a Foot Square, your firft Bufinefs is to draw an Ichnographical Plan, which is
thus performed :

An exact Square being made to the Size of your intended Plan, proceed to divide
both Horizon and Bafe into eight equal Parts, and from each Divifion in the Bafe to
its oppofite Point in the Horizon rule perpendicular Lines, and divide the Sides into
the fame Number, ruling acrofs from Point to Point parallel Lines ; fo that of Courfe
your Pavement will be divided into 64 Square Feet; as the eight Feet in Length,
being multiplied by the eight in Breadth, produce the Number of Pieces contained
in the Whole : then rule from Corner to Corner Diagonal Lines, and you will have
your Ground-plot as in the fame Figure.

Now, to throw this into Perlpective, draw another Square as before directed, and
divide the Bafe Line only into eight equal Parts ; fix your Point of Sight at F. in the
Center of the Horizon G. H. ; then to every Divifion in the Bafe D. E. rule Lines
from the fame Point; and proceed to rule Diagonals from D. to H, and from G. to
E, to anfwer thofe in the Ground-plot, and you will then hive your Square reduced
to the Triangle D. E. F. and from the Point I. where the Line D. F. is interfected
by the Diagonal G. E. to the oppofite Interferon K. where the Line E. F. is inter-
fered by the Diagonal D. H.; then rule a parallel Line, which is the Abridgment
of the Square.

From the reft of the Lines which go from the Bafe to the Point of Sight, through
the Points which are interfecled by the Diagonals, rule parallel Lines, and you will
then have your Square Pavement laid in true Perfpeclive, as in Fig X. Plate IV.

To find the Height and Proportion of Objects appearing above the Horizon on a
fuppofed Plane. See Fig. XI. Plate IV.

Having your horizontal Line ruled A B. proceed with fixing your Point of Sight
as at N, and marking the Place of your neareft Pillar by a Dot at the Summit or Top
as at C, and another at the Bafe as at D. Then rule a Line from C. to N. and
another from D. to N. and thefe two Lines give the Height of any Number of Pil-
lars : for Inftance, would you have your Pillar at E, fix your Dot for the Bafe, then
meet the Diagonal D. N. at F, by ruling a parallel Line, and to the Diagonal C N
rule the Perpendicular F G, which Perpendicular fhews the Height of the Pillar
required at E. Or, would you have a Pillar placed at H, obferve the foregoing Di-
rection* ; ruling the Parallels H I and K L, and the Perpendicnlars I M and L O
will fhew the required Heights and Diftances.

In finding the Diameter at any particular Diftances, you are to be guided by that
neareft the Bafe ; as, for Example, fuppofe your neareft Pillar D R to be ten Feet in
Height and one in Diameter, interfecl: from Bottom to Top in two equal Parts, and
upon the Bafe of the Pillar fet off one of them from the Point of Sight N to the
Diameter R, then rule a Line to the Point of Sight from R, and you will have on
4be refpecuve Bafes the Thicknefs of each Pillar.

The