The theory
and practice of vision in Leonardo and his followers
Coordinator: Prof. Carlo Pedretti
THURSDAY,
MAY 31 2001
The
second day of this session concentrates on a number of special problems
pertaining to Leonardo's achievements in the theory and practice of
vision.
Multa
renascentur quae jam cecidere. Horace's famous dictum seals up Calvi's
classic study of 1925 on the chronology of Leonardo's manuscripts. It
is so true, indeed, that late in life Leonardo takes up, time and again,
what had interested him long before then, even in his earliest days.
"Keep in mind how the ball of Santa Maria del Fiore was soldered
together in sections". This in a notebook of 1515 with reference
to a 1469 event to which Leonardo himself participated as an apprentice
in Verrocchio's workshop. This has a bearing on perspective as well,
and implies experimentation through models. The soldering process he
refers to was made by means of burning mirrors.
Numerous early sheets in the Codex Atlanticus dating from the late 1470s
contain studies for the making of burning mirrors. It can be ascertained
that the curvature of the polishing blade - what Leonardo later calls
"sagoma" - was a parabola. This is explained by Leonardo himself
with the diagram of a device for a 45-degree section of a cone. Note
and diagram date unquestionably from 1478-1480 (not after 1500, as some,
e.g. Carpiceci, suggest). Here again is the case of an early idea resumed
very late in life. The identical diagram is in a way the "framework"
for the construction of an elipsograph or parabolagraph shown in two
famous drawings of about 1515, at the time of Leonardo interest in the
construction of burning or parabolic mirrors with which to utilize solar
energy for industrial purposes - parabolic mirrors also used for astronomical
observation and possibly for telescopic vision, as later described by
Calcagnini. Leonardo's extensive studies of the caustic of reflection
beginning around 1503-1505, after the first publication of Archimedes'
Quadratura parabolae, may suggest the need to recreate some of his experiments
with models. It may also be appropriate to consider the evidence of
his having invented a "tornio per far gli ovali", a device
recorded to have been still in use at the end of the sixteenth century
(Lomazzo in Italy, and Besson in France). This too would be suitable
for interpretation and translation into a model. The same can be said
of a device hinted at on an early sheet. This is a large drawing in
the Codex Atlanticus which looks like a perspective construction and
which I had taken (1978) to refer to the project for a sundial. Only
recently it has been interpreted (Sinisgalli) as Leonardo's method of
drawing a parabola based on Ptolemy.
Related to problems of Optics and Catoptrics, as best exemplified by
Leonardo's extensive studies of the "problem of Alhazen" beginning
about 1503, is the perspective problem of anamorphosis, that Leonardo
codifies for the first time with a note in the Arundel manuscript about
1506-1508. This codification refers to lateral distortion, a problem
in the theory and practice of painting that must have intrigued Leonardo
since the start of his career. Since a picture may be intended for a
location where it would be seen at an angle upon being first approached
from a side, it could be profitably planned accordingly so as to introduce
the kind of distortion that allows the displaced eye to restore the
correct vision. An unquestionable error of perspective in the Uffizi
Annunciation (the long arm of the Virgin) of the 1470s has been
explained (Natali) precisely as the result of such anamorphic condition.
An overview of Leonardo's preoccupation with anamorphosis throughout
his life - gathering all sorts of information from his manuscripts and
contemporary documents - shows that he must have worked out a system
to construct models of cylindrical anamorphosis, considering that late
in life, possibly in France, he was able to solve the "problem
of Alhazen" by means of an instrument. It is probably not a coincidence
that contemporary records of his work in France refer to anamorphical
subjects, namely the "horses made for Francis I" (Lomazzo).
Newly discovered documents as well as historical and philological evidence
can be brought to bear on a technical and iconographical interpretation
(Julius Caesar's De bello gallico) of Leonardo's last and lost
composition. And it could well be surmised that among the "instrumenti",
i.e. models, left by Leonardo at his death in France in 1519, as mentioned
in his Last Will, there might have been that for the solution of the
"problem of Alhazen" and those for the design of cylindrical
anamorphoses.
Leonardo's ties with France may be shown to start with Jean Pellerin
Viator's treatise on perspective of 1505, which contains a codification
of the "two-point perspective" that Leonardo himself had told
Caporali (1536) "to have used more than anybody else". Some
of Viator's views on vision may be considered in relation to Leonardo's,
and the same can be said of practical applications. There remains, however,
the punctus dolens as to whether Leonardo really codified and
employed the sort of curvilinear perspective displayed in the work of
French book illuminators of the fifteenth century, particularly Fouquet.
A review of the often conflicting interpretations of his late writings
on perspective (White, Gioseffi, Maltese, Pedretti, etc.) may help to
get closer to the truth. Much is yet to be done on Leonardo's studies
on the horizon, for which there is but scanty evidence, that is, the
last part of his Book on Painting and a few notes on sheets from
his last period in France. His vision of the Egyptian horizon, whether
imagined of experienced - "E questi tali orizzonti fanno molto
bel vedere in pittura" - is truly a way of observing the world
from the airplane.
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