ster manuscript, since the development of the ideas appears to have reached the same stage, embracing, in large part, the same issues, and because the individual titles of the chapters or books correspond more often than not with the topics mentioned or dealt with in the Leicester Codex; and because, lastly, in some cases the subjects are grouped together in the same way. These coincidences appear so strange as to suspect that one might have to look for them in the frequent references found in descending numerical order (35 M, 29 M, 25 M, 23 M, 22 M, 23 m, 23 m, 21 m, 21 m, 20 m, etc., as far as 1° m (sheet 74 r. -a and 74 v. -a; to sheet 79 r. -a, 17m is found only once) throughout the said list of the Atlantico Codex, as so many references to the pages of the Leicester manuscript, of which it would have provided a sort of index. But, beginning to make a comparison from an analytical point of view, especially as regards the arrangement of the subjects in the manuscript with respect to the order of the references offered by the cited list of the Atlantico Codex, no elements can be found to confirm such doubt; so much so as to think that the list itself is only a little anterior or preparatory to, or parallel to the Leicester manuscript, to which it may have served to a large extent, helping to reassemble from other places ( and perhaps, mainly from a notebook indicated as M) the topics of the Treatise. The analogies are too many and too evident, especially those provided by the very varied themes which follow on from one another on sheet 74 r. -a of the Atlantico Codex, for them not to be related to the Leicester manuscript; and this relation, at least for sheet 74 r. -a, points in favour of the list in the Atlantico Codex being earlier, in which the arrangement of the subject appears less advanced than in this Codex. The considerations already made would seem to exclude that the Leicester manuscript could have been started prior to 1503. From that year, up to about halfway through 1508, lies the range of most probable hypotheses regarding the period when the manuscript was compiled. From the beginning of March 1503 to the 30 May 1506, Leonardo continued his studies of hydraulics in Florence, alternating them with studies of flight , with work on the Battle of Anghiari, with studies of solid geometry and other mathematical occupations. During this period the following note is believed to have been written in the manuscript K, belonging in part to the Florentine stay terminating in 1506 and in part to the time in Milan immediately following it : “la gocciola che chade in locho d'equal densità e planjtia risalterà cholli stremj del suo vesstigio for della sua circhunferentia con equal disstantia e così de converso”. (a drop falling in a place which has the same density and is on a flat level will bounce back with the same force and to the same extent as it has penetrated below this point and vice versa)