It was after this, in his early manhood, that Leonardo became interested in the things of nature around him and made many investigations into their meaning. He took up astronomy for a time and anticipated some of the thoughts that Copernicus was to put in order in his great theory. Such ideas in astronomy were in the air at that time. Cardinal Nicholas of Cusa had more than hinted at them when, about the middle of the fifteenth century, he declared that the earth moved in the heavens like the other stars. Astronomical subjects were { 28} favorite speculations for intellectual genius. Regiomontanus, who died before he was forty, was alive in Leonardo's boyhood, and after having begun that series of astronomical leaflets which later were to influence so deeply Columbus and the Portuguese navigators, was invited down to Rome to reform the calendar. Toscanelli made the observations on comets, out of which later their orbits were confirmed. Every form of natural observation caught the inquiring Leonardo's eye, and he studied the plants around him and meditated on crystal formation and occupied himself with all the forms of living things. Somehow his feeling seemed to be that such broadening of his intelligence would help him to breadth of expression in art, though probably it was only his native curiosity occupying itself in the insatiable youthful years with everything that came to hand. His achievements in science are sketched hurriedly in the chapter on Physical Science.
Leonardo seems to have occupied himself much with mechanical toys. He made mechanical birds that flew, mechanical lions that walked and a lizard which crawled and whose horns and eyes moved while the oscillating wings were constantly in motion. Every one of these contrivances, however, was the result of serious study. He took up with great assiduity the problem of flying and was quite sure that he would be able to make a machine by which men would accomplish locomotion through the air. He studied the wings of birds very carefully, and anticipated the knowledge of most of the principles of flight as they developed in later years. He used his mechanical lion as a bait to catch the attention of Francis I. The beast is said to have walked across the audience chamber towards the monarch until, when close to him, it stood up and disclosed the fact that the "Lily of France" was stamped upon its heart. Leonardo's own name is derived from lion and this was supposed to be his declaration of patriotic affection and loyalty to the French King.