Langley next made a model which took the form of a tandem biplane, and which had some success in flights. When the Government appropriated $50,000 for him to build an aerodrome that would carry a man, Langley began to experiment with a gasoline engine. He used his tandem biplane and a motor that developed two and a half to three horsepower. The whole machine weighed fifty-eight pounds, and the planes, which were set at a dihedral angle, had sixty-six square feet of surface. A successful test without a pilot was made on the Potomac River below Washington on August 8, 1903, and while the spectators and reporters were lauding him the inventor merely remarked: "This is the first time in history, so far as I know, that a successful flight of a mechanically sustained flying machine has been seen in public." The man-carrying machine was ready for its tests a few months later. Ever since having been financed by the Government, Langley had been at work, and the result was a tandem monoplane much like his early models. It was driven by a gasoline motor placed amidships which acted on twin screw propellers, which also were between the tandem planes. The whole machine with the pilot weighed 830 pounds, and had 1,040 square feet of wing surface. It was fifty-two feet long from front to rear and the wings measured forty-eight feet from tip to tip. The wings were arched, like those of modern aeroplanes, and the double rudder at the rear had both horizontal and vertical surfaces to steer the machine up or down, or from right to left. The aerodrome did not have any device for keeping it on an even keel, such as the ailerons we know to-day, or the wing-warping system of the Wright machine. This was a serious drawback, according to the present-day scientists, but Professor Langley had set his wings in a dihedral angle--that is, like a broad V, to give what is called automatic stability. This dihedral angle, it will be remembered, is one of the principles discarded by the Wright brothers early in their experiments as one that tended to keep the machine oscillating from side to side. Professor Langley realized this, it is said, and to offset it had already advanced several ideas along the line of wing warping, for keeping his machine on an even keel when buffeted by the wind. The aerodrome also lacked the wheels now used on aeroplanes for starting and alighting, and even the skids that were used on the first Wright machines. His motor was remarkably well adapted to the work. It developed 50 horsepower with a minimum of vibration, and with its radiator, water, pump, tanks, carbureter, batteries, and coil weighed twenty pounds, or about five pounds per horsepower. The arrangement of the five cylinders around the shaft like the points of a star was one that has become very popular in modern aviation motors.