APART from Michelangelo, Leonardo is the only great painter of the Italian Renaissance who has left in writing any quantity of material dealing with the arts, and we should expect that the opinions and ideas of such a man would throw more light on Renaissance art-theories than all the systematic and philosophical treatises of the laymen who wrote in the sixteenth century. Many of his theories do, of course, give us information about the methods and ideas of the period which we cannot derive from other sources, but the confusion of the surviving manuscripts and the lack of plan in the notes make it impossible to deduce a really coherent theory of the arts from Leonardo's written works.
Leonardo evidently intended to write a full-dress treatise on painting, and, according to Luca Pacioli, some sections of it at least were finished by 1498. If this is so, the parts in question are lost, but many schemes for the general plan of the treatise, not all of them consistent with each other, survive in the existing material. What we actually have left of Leonardo's writing is an enormous mass of notes, mostly jotted on the margins of sketch-books. These notes are either passages which Leonardo copied down from what he read, or original ideas embodying a personal theory or observation.
The datable manuscripts cover a period from 1489 to 1518. The originals are to be found in many public and private libraries, particularly in Paris and at Windsor, and most of them have been published. 1 Even more important, however,____________________