_The plan of a scheme of arrangement suggested in No._ III _and adopted by me has been strictly adhered to for the first four Books. For the three last, however, few materials have come down to us; and it must be admitted that these three Books would find a far more appropriate place in a work on Physics than in a treatise on Painting. For this reason I have collected in Book V all the chapters on Reflections, and in Book VI I have put together and arranged all the sections of MS._ C _that belong to the book on Painting, so far as they relate to Light and Shade, while the sections of the same MS. which treat of the_ "Prospettiva de' perdimenti" _have, of course, been excluded from the series on Light and Shade._ [Footnote III: This text has already been published with some slight variations in Dozio's pamphlet _Degli scritti e disegni di Leonardo da Vinci_, Milan 1871, pp. 30--31. Dozio did not transcribe it from the original MS. which seems to have remained unknown to him, but from an old copy (MS. H. 227 in the Ambrosian Library).] GENERAL INTRODUCTION. Prolegomena. 110. You must first explain the theory and then the practice. First you must describe the shadows and lights on opaque objects, and then on transparent bodies. Scheme of the books on Light and shade. 111. INTRODUCTION. [Having already treated of the nature of shadows and the way in which they are cast [Footnote 2: _Avendo io tractato._--We may suppose that he here refers to some particular MS., possibly Paris C.], I will now consider the places on which they fall; and their curvature, obliquity, flatness or, in short, any character I may be able to detect in them.]