About 1780, Karl Friedrich Meerwein, an architect, and the Inspector of Public Buildings for Baden, Germany, made many scientific calculations and experiments on the size of wing surface needed to support a man in the air. He used the wild duck as a standard, and figured that a surface of 126 square feet would sustain a man in the air. This agrees with the later calculations of such experimenters as Lilienthal and Langley. Other of Meerwein’s conclusions are decidedly ludicrous. He held that the build of a man favors a horizontal position in flying, as his nostrils open in a direction which would be away from the wind, and so respiration would not be interfered with! Some of his reasoning is unaccountably astray; as, for instance, his argument that because the man hangs in the wings the weight of the latter need not be considered. It is almost needless to say that his practical trials were a total failure. [Illustration: Plan of Degen’s apparatus.] The next prominent step forward toward mechanical flight was made by the Australian watchmaker Degen, who balanced his wing surfaces with a small gas balloon. His first efforts to fly not being successful, he abandoned his invention and took to ballooning. Stentzel, an engineer of Hamburg, came next with a machine in the form of a gigantic butterfly. From tip to tip of its wings it measured 20 feet, and their depth fore and aft was 5½ feet. The ribs of the wings were of steel and the web of silk, and they were slightly concave on the lower side. The rudder-tail was of two intersecting planes, one vertical and the other horizontal. It was operated by a carbonic-acid motor, and made 84 flaps of the wings per minute. The rush of air it produced was so great that any one standing near it would be almost swept off his feet. It did not reach a stage beyond the model, for it was able to lift only 75 lbs. [Illustration: Stentzel’s machine.] In 1843, the English inventor Henson built what is admitted to be the first aeroplane driven by motive power. It was 100 feet in breadth (spread) and 30 feet long, and covered with silk. The front edge was turned slightly upward. It had a rudder shaped like the tail of a bird. It was driven by two propellers run by a 20-horse-power engine. Henson succeeded only in flying on a down grade, doubtless because of the upward bend of the front of his plane. Later investigations have proven that the upper surface of the aeroplane must be convex to gain the lifting effect. This is one of the paradoxes of flying planes which no one has been able to explain. In 1845, Von Drieberg, in Germany, revived the sixteenth-century ideas of flying, with the quite original argument that since the legs of man were better developed muscularly than his arms, flying should be done with the legs. He built a machine on this plan, but no successful flights are recorded.