Since the dawn of history the idea of human flight has intrigued mankind. As the influence of the Wrights’ achievements will last far into the future, so will the contributions of aeronautical pioneers who probed the mysteries of flight before Wilbur and Orville solved the problem. The research of these imaginative pioneer investigators influenced the brothers. In studying those earlier works the Wrights found many points that interested them. The knowledge that other pioneers had shared their faith in the possibility of heavier-than-air flight helped their morale. [Illustration: Lilienthal’s two-surface glider of 1895 in which some of his highest and longest glides were made. This German engineer made hundreds of glides with various apparatuses employing birdlike wings.] In the pioneers’ direct line of descent from the Greek legend of Daedalus and Icarus to the Wrights is Leonardo da Vinci. Da Vinci drew some interesting sketches in the late 15th century, though a machine built from his drawings could not possibly have flown. The interest in England of Sir George Cayley influenced other men to undertake the problem. A Frenchman, Alphonse Pénaud experimented with toy helicopters, using twisted rubber bands for motive power. It was a Pénaud toy helicopter, given to Wilbur and Orville by their father, that first stirred their childhood interest in flying. However, in Europe, most experimenters had turned from heavier-than-air machines to lighter-than-air dirigible balloons by the time the brothers took up the problem of heavier-than-air flight. The American-born Sir Hiram Maxim, after spending $100,000, had abandoned his work; the machine built by Clément Ader, at the expense of the French Government, had been a failure. None of the early experimenters attained sufficient knowledge of the aerodynamic principles involved to be able to design a successful powered machine capable of free, controlled, and sustained flight. [Illustration: Otto Lilienthal (1848-96).] Only a few of the general public could distinguish between a heavier-than-air powered flying machine and a lighter-than-air gas bag equipped with propellers. Few knew that the problem of powered flight was not to fill a balloon with gas or hot air and float in it, or to glide in a complicated kite against air currents. Many among those who realized the obstacles to heavier-than-air flight in a powered machine believed it was as impossible as perpetual motion.