One of the earliest trustworthy and scientific accounts of experimentation with an aërial glider was given by Sir George Cayley in _Nicholson’s Journal_, in 1809 and 1810. After a careful study of the principles of stability, he, in 1808, constructed a glider spreading 300 square feet of surface and weighing with its load 140 pounds. It had wing surfaces slightly inclined to each other, and a tail inclined enough to determine a gentle downward course. “When any persons,” says Cayley, “ran forward in it with his full speed, taking advantage of a gentle breeze in front, it would bear him up so strongly as scarcely to allow him to touch the ground, and would frequently lift him up and carry him several yards together. It was beautiful to see this noble white bird sail majestically from a hill to any given point of the plain below it, with perfect steadiness and safety, according to the set of the rudder, merely by its own weight, descending in an angle of about 18° with the horizon.” Sir George Cayley made a brave start in the science of dynamic flight, marshaling to it all the mechanical resources of his day. He applied the most reliable data of fluid resistance then available. He formulated the laws of equilibrium and control of a flying machine quite as well as any of his successors for two generations. He estimated the propulsive power required to carry a man, and computed the weight of the newly invented Bolton and Watt steam engine capable of supplying that power. He even conceived the idea of burning a gas or inflammable vapor behind a piston, thus anticipating the modern aëronautical motor. But the project as a whole was too formidable at that time for the genius of this one man, or of his generation of colleagues. Sailing flight they could have practiced with profit to the advancement of aviation, but power flight on a practicable scale had to await the long evolution of the internal combustion engine. The next great advancement in the devices and principles of aviation was made by another Englishman, and a worthy successor to Sir George Cayley. In 1842 Mr. Henson patented the aërial equipage shown in the accompanying illustration. It was what in present-day parlance is called a monoplane, being in fact the first commercially planned aëroplane known to history. As seen at a glance it consisted of a large sustaining surface rigidly trussed and driven through the air by two propellers actuated by a steam engine. It was to be guided up and down by means of a horizontal rudder, and guided to the right and left by means of a vertical rudder, seconded by a keel cloth; both rudders being at the rear of the large plane. The machine was designed to be launched by running down an inclined plane or track. Fuller details of this first patent aëroplane are given in the following official description in the South Kensington Museum of a model aëroplane constructed by Henson and Stringfellow: