_A ~Corinthian~ Pedestal, with its Pilasters._
The Performance of the Seventh Figure will be a great Assistance to you,
in the Construction and Division of this Pedestal A, and the Plan B;
since you have nothing more to add here, but the Pilasters C, and the
Mouldings which surround the two Sides. This Plan is put in Perspective
in D, and becomes more distinct by my sinking the Ground-line lower;
and the Profile E is also more distinct by the Removal of the Visual
FG, as mention’d in the foregoing Chapter. This I shall always do, that
there may remain Room for the shadow’d Figure, and that you may also see
that the Perpendiculars of the shaded Pedestal fall directly upon the
Angles of the Plan, and that the level Lines directly answer the Angles
of the Profile E. I repeat my Advice, that you would make the foresaid
Preparations on several Papers, and accustom yourself at the beginning
to take off the finish’d Figures with the Compasses; for it will become
very easy to you afterward, to design entire Machines of delightful
Perspectives, as you’ll see hereafter. And indeed in this Practice, the
Facility of this Rule, and of all that follows in this Work, does chiefly
consist.
_Respondetur objectioni factæ circa punctum oculi opticum._
Non omnium sensus est, uni optico operi unicum tantùm punctum
assignare, _e. g._ toti spatio fornicis, tholi, & tribunæ, quam
vocant, expressæ in figura nonagesimatertia, nolunt concedi
unicum punctum, volunt concedi plura.
_Respondeo, objectionem hanc dupliciter intelligi posse: vel enim
intelligi posset, non esse assignandum unicum punctum toti illi spatio;
atque in hoc sensu vera est; cum enim spatium illud valde oblongum sit,
dividi debuit in partes, atque assignanda tribunæ, quam dicunt, tholo,
& fornici, propria puncta; cum hoc communiter doceant, ubi situs nimium
est longus, & parùm altus. Vel potest intelligi de qualibet ex dictis
partibus, & sic intellecta penitùs falsa est. Primò, quia præstantiores
fornices aularum, & templorum, qui optico artificio ornati sint, si
unicum opus reddunt, à suismet authoribus determinatum idemque unicum
punctum accepisse compertum est. Secundò, quia cum ars optica sit mera
veri fictio, non id pictor facere potest, ut à qualibet parte simulet
veritatem, verùm ab uno determinato puncto id ostendit. Tertiò, quia si,
~e. g.~ fornici, qui uno integroque optico opere ornetur, plura puncta
assignaveris, nullum reperies locum, unde integrum opus spectare possis,
& ad summum ex quolibet puncto tantùm partem illius spectabis, nusquam
verò totum opus. Ex dictis igitur rationibus concludo ab inducentibus
plura puncta in eodem opere induci malum majus eo, quod unicum punctum
inducit; quare hoc omnino necessarium est situi in quo unicum opus
formandum sit, ad quod collimare debeant ex omni operis parte figuræ
simul & architectura. Quo posito, negari rationabiliter nequit, à
me etiam concedi unicum punctum spectando fornici amplo, aptoque ad
repræsentandum unicum opus, qualis est fornix in D. Ignatii templo. Si
verò propter situm irregularem, ut dicimus, architectura extra punctum
aliquantulum deformetur, & figuræ pariter operi optico intermixtæ extra
commune punctum aliquam patientur deformitatem, præterquam quod à
supradictis rationibus excusatur, nequaquam id vitio arti est, sed laudi;
quandoquidem ars à suo puncto exhibet, proportione positâ, ut rectum, ut
planum, ut concavum, id quod tale non est._
An Answer to the Objection made about the Point of Sight in Perspective.
_Every one does not approve, that in a Perspective of great
Extent one Point of Sight only should be assign’d the whole
Work; as for Example, In the whole Length of the Nave, Cupola,
and Tribune, express’d in the Ninety-third Figure, they will by
no means allow of one single Point, but insist upon several._
I answer, This Objection may be understood two ways; either that one
Point alone is not sufficient for that whole Length, and in this sense
’tis true; for that Space being very long, it ought to be divided into
Parts, and proper Points assign’d to the Tribune, Cupola, and Vault
of the Nave; as is commonly taught, where the Situation is of a great
Length, and not very high. Or it may be understood of any One of the said
Parts, and so is altogether false. _First_, Because in the Vaults of
Halls or Churches painted by the greatest Masters, if they consist of one
Piece only, we find but one Point of Sight assign’d. _Secondly_, Since
Perspective is but a Counterfeiting of the Truth, the Painter is not
oblig’d to make it appear real when seen from _Any_ part, but from _One_
determinate Point only. _Thirdly_, Because, if in a Vault, for Example,
where you would paint one entire Design of Architecture and Figures, you
assign several Points of Sight, you will find no place whence you may
take a perfect View of the Whole, and at best you can only view each
Part from its proper Point. From all which Reasons I conclude, that the
Introduction of many Points into the same Piece, is more injurious to the
Work, than making use of one only: Wherefore ’tis absolutely necessary in
a regular Situation, and where the Work is all of a piece, so to place
the same, as that the Figures and Architecture may from every part of
the Design have respect thereto. This suppos’d, I confess that I myself
make use of one Point of Sight only, in very large Vaults that consist
of one Design, such as that of the Nave of the Church of S. _Ignatius_.
If therefore through the Irregularity of the Place, the Architecture
appear with some Deformity, and the Figures intermix’d therewith seem any
thing lame and imperfect when view’d out of the proper Point, besides
the Reasons just now given, it’s so far from being a Fault, that I look
upon it as an Excellency in the Work, that when view’d from the Point
determin’d, it appear, with due Proportion, streight, flat, or concave;
when in reality it is not so.