It is hard for us to realize that to Lodovico, as to Caesar Borgia, Leonardo was primarily an engineer. Even the pageants that he planned for the Duke of Milan included ingenious automata. “Every day,” says Vasari, “he made models and designs for the removal of mountains with ease, and to pierce them to pass from one place to another; and by means of levers, cranes, and winches to raise and draw heavy weights; he devised methods for cleaning harbors, and for raising water from great depths.”42 He developed a machine for cutting threads in screws; he worked along correct lines towards a water wheel; he devised frictionless roller-bearing band brakes.43 He designed the first machine gun, and mortars with cog gears to elevate their range; a multiple-belt drive; three-speed transmission gears; an adjustable monkey wrench; a machine for rolling metal; a movable bed for a printing press; a self-locking worm gear for raising a ladder.44 He had a plan for underwater navigation, but refused to explain it.45 He revived the idea of Hero of Alexandria for a steam engine, and showed how steam pressure in a gun could propel an iron bolt twelve hundred yards. He invented a device for winding and evenly distributing yarn on a revolving spindle,46 and scissors that would open and close with one movement of the hand. Often he let his fancy bemuse him, as when he suggested inflated skis for walking on water, or a water mill that would simultaneously play several musical instruments.47 He described a parachute: “If a man have a tent made of linen, of which the apertures have all been stopped up, and it be twelve cubits across and twelve in depth, he will be able to throw himself down from any great height without sustaining any injury.”48
Through half his life he pondered the problem of human flight. Like Tolstoi he envied the birds as a species in many ways superior to man. He studied in detail the operation of their wings and tails, the mechanics of their rising, gliding, turning, and descending. His sharp eye noted these movements with passionate curiosity, and his swift pencil drew and recorded them. He observed how birds avail themselves of air currents and pressures. He planned the conquest of the air:
You will make an anatomy of the wings of a bird, together with the muscles of the breast, which move these wings. And you will do the same for a man, in order to show the possibility of a man sustaining himself in the air by the beating of wings.49… The rising of birds without beating their wings is not produced by anything other than their circular movement amid the currents of the wind.50… Your bird should have no other model than the bat, because its membranes serve as… a means of binding together the framework of the wings.51… A bird is an instrument working according to mechanical law. This instrument it is within the power of man to reproduce with all its movements, but not with a corresponding degree of strength.52
He made several drawings of a screw mechanism by which a man, through the action of his feet, might cause wings to beat fast enough to raise him into the air.53 In a brief essay Sul volo, On Flight, he described a flying machine made by him with strong starched linen, leather joints, and thongs of raw silk. He called this “the bird,” and wrote detailed instructions for flying it.54
If this instrument made with a screw… be turned swiftly, the said screw will make its spiral in the air, and it will rise high.55… Make trial of the machine over the water, so that if you fall you do not do yourself any harm.56… The great bird will take its first flight… filling the whole world with amazement and all records with its fame; and it will bring eternal glory to the nest where it was born.57
Did he actually try to fly? A note in the Codice Atlantico58 says: “Tomorrow morning, on the second day of January, 1496, I will make the thong and the attempt”; we do not know what this means. Fazio Cardano, father of Jerome Card an the physicist (1501–76), told his son that Leonardo himself had essayed flight.59 Some have thought that when Antonio, one of Leonardo’s aides, broke his leg in 1510, it was in trying to fly one of Leonardo’s machines. We do not know.
Leonardo was on the wrong tack; human flight came not by imitating the bird, except in gliding, but by applying the internal combustion engine to a propellor that could beat the air not downward but backward; forward speed made possible upward flight. But the noblest distinction of man is his passion for knowledge. Shocked by the wars and crimes of mankind, disheartened by the selfishness of ability and the perpetuity of poverty, saddened by the superstitions and credulities with which the nations and generations gild the brevity and indignities of life, we feel our race in some part redeemed when we see that it can hold a soaring dream in its mind and heart for three thousand years, from the legend of Daedalus and Icarus, through the baffled groping of Leonardo and a thousand others, to the glorious and tragic victory of our time.