So far, the stories of the development of flight are either legendary or of more or less doubtful authenticity, even including that of Danti, who, although a man of remarkable attainments in more directions than that of attempted flight, suffers--so far as reputation is concerned--from the inexactitudes of his chroniclers; he may have soared over Thrasimene, as stated, or a mere hop with an ineffectual glider may have grown with the years to a legend of gliding flight. So far, too, there is no evidence of the study that the conquest of the air demanded; such men as made experiments either launched themselves in the air from some height with made-up wings or other apparatus, and paid the penalty, or else constructed some form of machine which would not leave the earth, and then gave up. Each man followed his own way, and there was no attempt--without the printing press and the dissemination of knowledge there was little possibility of attempt--on the part of any one to benefit by the failures of others. Legend and doubtful history carries up to the fifteenth century, and then came Leonardo da Vinci, first student of flight whose work endures to the present day. The world knows da Vinci as artist; his age knew him as architect, engineer, artist, and scientist in an age when science was a single study, comprising all knowledge from mathematics to medicine. He was, of course, in league with the devil, for in no other way could his range of knowledge and observation be explained by his contemporaries; he left a Treatise on the Flight of Birds in which are statements and deductions that had to be rediscovered when the Treatise had been forgotten--da Vinci anticipated modern knowledge as Plato anticipated modern thought, and blazed the first broad trail toward flight. One Cuperus, who wrote a Treatise on the Excellence of Man, asserted that da Vinci translated his theories into practice, and actually flew, but the statement is unsupported. That he made models, especially on the helicopter principle, is past question; these were made of paper and wire, and actuated by springs of steel wire, which caused them to lift themselves in the air. It is, however, in the theories which he put forward that da Vinci's investigations are of greatest interest; these prove him a patient as well as a keen student of the principles of flight, and show that his manifold activities did not prevent him from devoting some lengthy periods to observations of bird flight.