Leonardo da Vinci spent many unfruitful years, ＿＿（39）＿＿ his first stay in Milan and his second period in Florence, experimenting with a flying machine. The attempt to support and move the human body in the air ＿＿（40）＿＿ because, in the absence of an internal combustion engine, Leonardo could not create mechanisms of propulsion capable of providing the necessary upward lift. Nevertheless, based on this understanding of air currents pressure, and resistance, he ＿＿（41）＿＿ designs for machines that anticipated the modern glider, parachute, and helicopter. Related to these studies were notes concerning the cosmos, later developed by Galileo.