Preface

In February 1973, under the auspices of the Wellcome Institute in London, Dr. K.D. Keele, M.D., F.R.C.P., and the author set out to answer a straightforward question: whether Leonardo da Vinci's writings on linear perspective had an experimental basis. A single experiment was first repeated successfully. This led to further experiments and, in turn, to a complete search of Leonardo's perspectival notes (1975-1976). Dr. Keele, who had in the meantime become engaged with the new edition of the Corpus of Anatomical Manuscripts in the Collection of Her Majesty, the Queen, at Windsor, acted as mentor, advisor and friend. The perspectival writings revealed many connections with optics. A complete search of the optical notes thus followed (1976-1977). Two volumes were now projected: a first on linear perspective; a second on optics. Subsequently, it was decided to add a third, which would serve as a concordance.

In Wolfenbuttel, a draft for volume one was written (1977-1978). The draft for volume two proved more difficult (1978-1980). In the case of linear perspective there had been only a very short tradition, consisting essentially of four fifteenth century authors, Alberti, Filarete, Francesco di Giorgio Martini and Piero della Francesca. The optical tradition, by contrast, extended over nearly two millennia and included such important thinkers as Euclid, Ptolemy, Alhazen, Witelo and Pecham.

Leonardo had modestly described himself as a man without letters (omo sanza lettere). But then, so too had Cicero. Leonardo's position with respect to ancient and mediaeval optical traditions was therefore examined. This revealed a much greater debt than had been expected. It was found, for instance, that Leonardo's concept of percussion, underlying his physics of light, was based on specific similes that could be traced directly to Aristotle. More important: Leonardo's treatment of these ancient similes followed a distinct pattern. That which his predecessors had been content to employ as a verbal image, Leonardo insisted on exploring visually. A traditionally vague image was now put to the test and challenged by experiment. In other words the rise of visualization and the development of experiment in the Renaissance were directly linked.

This visualization was also related to a new interest in taking verbal images, words, literally. Seneca had found it sufficient to note that sound is propagated like the waves produced by a pebble in water. Leonardo, on the other hand, could not be content until he had thrown various pebbles into water and recorded the waves they produced. In the epilogue to volume one it was noted that this new approach to literalism, which some see as a direct product of fourteenth century nominalism, also had profound religious consequences. Hence the scientific revolution and the religious revolts in the sixteenth century had common roots in a nexus between visualization and literalism explored by Leonardo. The attempts by Ong¹ and Foucault² to pinpoint a basic shift in

approach to the word and language thus involved a shift initiated by visual images.

Leonardo's visualization of Ancient and Mediaeval similes offers new insights into the relations between tradition and innovation, continuity and discovery; serves, in fact, as a dramatic illustration of Whitehead's claim that Western civilization is essentially a series of footnotes on Plato and Aristotle. And the Renaissance, to which Leonardo was so central, now emerges as a distinct shift in approach to traditional knowledge rather than an actual break. Albertus Magnus, Leonardo and Galileo did not use dramatically different sources. But their attitude to these sources marks the difference between mediaeval interest in the natural world and early modern science.

As the draft for volume two progressed it became clear that Leonardo's optical studies are not just concerned with understanding sight and light per se. They have an ulterior motive: astronomy, but then in a special sense, namely, optical phenomena relating to the heavenly bodies: Why does the full moon shine? Why do the stars twinkle? Why are there eclipses? and so on. Here again Leonardo is building on a tradition and his contributions to it, in turn, help explain why Kepler, a century later, should have devoted his classic work (1604) to the astronomical part of optics.

By the time that the draft for volume two had been completed (January 1980) the consequences of visualization loomed anew. The notebooks contain approximately 100,000 diagrams. No author before Leonardo, nor practically anyone since, had produced this number. Leonardo had, moreover, explicitly emphasized the primacy of visual images over verbal ones, of pictures over words. It seemed likely, therefore, that these diagrams would offer insights into Leonardo's method. A four months scissors and paste project ensued (February-May 1980). The diagrams were organized in sequence. Systematic themes were now found to underlie the seemingly chaotic notes. In light of this both volume one (June 1980-March 1981) and volume two (September 1981-July 1983) were written afresh.

This work would have been unthinkable but for the generous and continued support of foundations. It had begun in 1973 as a hobby while the author was preparing a doctoral thesis at the Warburg Institute with support from the Canada Council. From August 1975 through July 1977 a Research Fellowship from the Wellcome Trust enabled the author to pursue these studies on a full time basis. For the period, August 1977 through July 1979 a similar grant from the Volkswagen Foundation made it possible to continue at the Herzog August Bibliothek in Wolfenbuttel. There, work proceeded for the next two years with a Sonderforschungsstipendium from the Alexander von Humboldt Foundation and then, for another six months, still under their auspices, but with funds from the Fritz Thyssen Foundation. With the generous support of the Gerda Henkel Foundation (July 1982-July 1983) the optical sutides were completed.

I am very grateful for the moral support provided by various members of these institutions, and in particular Dr. Marie-Luise Zarnitz (Wolkswagen), Dr. Thomas Berberich (Alexander von Humboldt) and Frau Lisa Maskell and Dr. Ulbrich (Gerda Henkel).

In the preface to volume one a list was given of the many persons who contributed both directly and indirectly to this project. As the same list applies to volume two it will not be repeated here. A few individuals require special mention. Professor R.H. Weale (London) and Professor A.I. Sabra (Harvard) kindly read and criticized parts of the text. In Wolfenbuttel, I wish to thank in particular Dr. Sabine Solf, and Professor Paul Raabe. Among the many friends who provided moral support I thank especially Udo Jauernig. My great debt to Dr. Kenneth Keele and his wife Mary I cannot frame in words. Without him, this project could simply not have been carried out. I am very grateful to Ms. Shirley Fulford for typing the manuscript and to Dr. Michael Meier of the Deutscher Kunstverlag for his personal help in seeing this work through the press.