Disregarding the crude essays at human flight, recorded in the early literature and history of many peoples, we may notice first the well authenticated sketches of Leonardo da Vinci. His fertile mind conceived three distinct devices for carrying a man in the air. But he and his successors for nearly four centuries could do little more than invent. For lack of motive power they could not navigate dynamic flyers, however ingeniously contrived. [Illustration: FIG. 26.—DA VINCI’S HELICOPTER.] Da Vinci’s first design, as shown in Fig. 26, provides the operator with two wings to be actuated by the power of both arms and legs, through the agency of very ingenious harness. With this device an acrobat could fly forward and downward, to the delectation of a multitude; but he would have to be caught on something soft to escape injury. Since Leonardo’s day the experiment has been tried occasionally, with varied results, sometimes grotesque, sometimes tragic. He doubtless realized the impracticability of an orthopter actuated by human muscle, and yet he has had many followers. The orthopter is still a favorite device cultivated by a few persons who propose to work its wings by means of a gasoline motor. Doubtless the feat is physically possible, and may be accomplished in time. [Illustration: FIG. 27.—DA VINCI’S PARACHUTE.] Da Vinci’s second flyer was a helicopter, as shown in Fig. 26. An aërial screw 96 feet in diameter was to be turned by a strong and nimble artist who might, by prodigious effort, lift himself for a short time. Though various small paper screws were made to ascend in the air, the larger enterprise was never seriously undertaken. Many subsequent inventors developed the same project; but the fellow turning the screw always found it dreadful toil and a hopelessly futile task. Of late the man-driven helicopter has been abandoned, but the motor-driven one is very much cultivated. Scores of inventors in recent years, aided by light motors, have been trying to screw boldly skyward, and some have succeeded in rising on a helicopter carrying one man. Da Vinci’s third scheme for human flight, as shown in Fig. 27, was a framed sail on which a man could ride downward, if not upward. This device never fails to navigate with its confiding sailor. Sometimes he lands in one posture, again in another; but voyage he must, with the certainty of gravitation. Leonardo is, therefore, the father of the parachute. This, in turn, has had a varied offspring. The common parachute, the aërial glider, the soaring machine, or passive aëroplane, that rides the wind without motive power and without loss of energy.