In the fifteenth century students and inventors gave serious attention to the navigation of the air and trustworthy accounts of their labors come down to us. Jean Baptiste Dante, a brother of the great Italian poet, made a number of gliding flights from high elevations and while giving an exhibition at a marriage feast in Perugia, like his predecessors in the middle ages, alighted on a roof and broke a leg. Leonardo da Vinci, the great painter and sculptor, was an amateur aviator of no mean attainment for his day. He invented a machine which the operator was to fly by using his arms and legs to set wings into flapping motion, like those of birds. This was called an orthopter, or ornithopter, a name which may be properly applied to any similar device. Another machine invented by him was in the form of a horizontal screw ninety-six feet in diameter. By the twisting of this the machine was designed to fly upward. This was called a helicopter. Da Vinci’s third invention in this line was the parachute, with which successful descents were made from towers and other elevations. In the early half of the eighteenth century the Swedish philosopher, Emanuel Swedenborg, sketched in one of his works a flying machine of the orthopter style which he knew would not fly but which he suggested as a start, saying “It seems easier to talk of such a machine than to put it into actuality, for it requires greater force and less weight than exists in the human body.” In 1742 the Marquis di Bacqueville at the age of sixty-two attempted to make a gliding flight from the tower of his home in Paris across the river Seine to the gardens of the Tuileries, started successfully in the presence of a great multitude, but suddenly halted over the river and fell into a boat, paying the historic penalty of a broken leg. At this point it may be well to classify the flying devices thus far considered. Early Flying Machines 1. The _orthopters_, or as they are less commonly called, the ornithopters. The word “orthopter” means straight wing and the word “ornithopter” bird wing. This class of machines includes those designed to fly by the flapping of wings, somewhat in imitation of birds. 2. The _helicopters_. The word “helicopter” means spiral wing. Flying machines of this class are designed to fly by the rapid horizontal rotation of two spiral propellers moving in opposite directions but so shaped that their combined effect is to move the machine upward. They are like a pair of tractor propellers of the modern aeroplane but arranged horizontally to lift the machine instead of drawing it forward in a vertical position.