This note, which may be found almost identical on sheet 33 r. of the Leicester manuscript and which undoubtedly precedes it (both because the sheet mentioned by the K manuscript was initially written quickly in pencil and then rewritten in pen, and because it is clear that the single observations were copied from a small pocket book, which the K manuscript was, to the Leicester manuscript, rather than the other way round), is the last clue which, at the present state of investigation (save what was mentioned hypothetically, about 1506, on pages 14 and 15), suggests it probable that the Leicester manuscript or at least most of it was written between 1504 and 1506, with some reasons for preferring the two year period 1505-6. Those subjects in common which would seem almost to exclude a continuous investigation of some topics, from the last sheets (in terms of time) of the Leicester manuscript and the first (still kept, as we have said, in the original order) of the Arundel Codex and then the manuscript F, would leave room for the hypothesis that the Leicester Codex may, rather, not have been begun until the later Florentine period 1507-1508; the same in which the Arundel Codex was begun in Piero di Braccio Martelli’s house. This seems possible but much less probable; while the theory that Leonardo wrote a part (not more than the last third) of the manuscript after he had been to Milan in 1506 may have some grounds, or that leaving Florence with a pass that would not have been for a period longer than three months according to the pacts imposed by the Florentine Seignoury, he left in Florence or deposited in Vinci (if the objection already raised in note. 7 on page 15, did not prevent one from thinking that he still had a safe house there) a part of his furnishings, books and manuscripts; and with them the Leicester manuscript (given that Leonardo did not believe it essential for him to have this book on water with him during his brief stay in Lombardy), which could have been finished upon his return to Florence. From the approximate conclusions at which one arrives, the deductions that might be made on the series of relations existing between the Leicester manuscript and the other Vinci codex would seem to concur, both as regards the derivation of the subjects and as regards the succession and development of the ideas. One could enter into the course of comparative considerations, if in this case the work did not take on proportions which would make it an end in itself, requiring an exhaustive investigation incompatible with the