limits of space and time which we have set ourselves. It is also worth abstaining, for the reason now advanced, to which limits of competence not to be surpassed without consideration should be added, from starting a detailed examination of the contents and worth of the Treatise on water which Leonardo drafted in this manuscript, or of his relations with the origins and progress of science reflected in it. It is not possible, on the contrary, to omit some considerations which prove essential to the understanding of the text on two fronts, one widely used, the other mentioned in the Leicester manuscript. Leonardo’s admiration for Ptolemy’s Cosmography is well known. This was Leonardo’s most important geographic source; and in fact with the help of Ptolemy’s maps, mountains, seas, river courses and the distribution of the land and seas were studied in the Leicester manuscript. When, with kind help, we set to looking for items of information which would explain Leonardo’s mention, on sheet 34 r., of the river Trigon, and the Munace swamp, nominated by him with the other two swamps Pallas and Triton, we were led to consult the edition of Ptolemy’s Cosmography printed in Ulm in 1482, and we found clarification not just of this specific point, but traces of most of the cosmographic considerations (except for those regarding the regions of Italy known to him contained in the Leicester manuscript, and the reason for the characteristics offered by the geographic nomenclature. We are referring to the 1482 edition, not the Roman edition of 1490, because certain coincidences may be attributed to the first or other editions or maps (and the hypothesis that Leonardo had designed one or more, drawing on the Cosmography, adding then, perhaps some new information, and using them for the Leicester manuscript, would be plausible), which are closely related to his illustrations.