The operator was supposed to lie on his face in the middle of the lower plane, but in the later machines a seat was provided for him alongside the engine, and in still later ones seats for one or two passengers. The engine which was designed by the Wright brothers themselves for this purpose, was a water-cooled four-cylinder motor which developed sixteen horsepower from 1,020 revolutions per minute. The engine was connected with the propellers at the rear of the biplane by chains. The propellers were about eight feet in diameter and the blades were six to eight inches wide. The materials used in the biplane were mostly durable wood like spruce pine and ash, the metal in the engine and the canvas on the planes. There was not one superfluous wire. Everything had a use, and even the canvas was stretched diagonally that it might fit more tightly over the framework of the planes and offer less wind resistance, and also stretch more easily for the wing warping. Finally on December 17, 1903, everything was in readiness for the first attempt of these two patient men--then unknown to the world--to fly in a power-driven machine. That first flight, made practically in secret amid the desolate sand dunes of the North Carolina coast, lasted only twelve seconds. However, it was the first time, but one, in the history of the world that a machine carrying a man had lifted itself from the ground and flown entirely by its own power. The two succeeding flights were longer, and the fourth covered 853 feet, lasting fifty-nine seconds. The inventors were not heralded as the greatest men of their time. There were no medals or speeches. The five men--fishermen and life savers--who saw the flights agreed that it was wonderful, but they kept the Wrights' secret and the brothers calmly continued their studies and experiments. The spring of 1904 found them at work on Huffman Prairie about eight miles east of Dayton. The first trials there were not very successful and the brothers, who had worked seven long years in secret, had the unpleasant experience of failing to show satisfactory results to the few friends and reporters invited to see an aeroplane flight. Their new machine was larger, heavier, and stronger, but the engine failed to work properly. Of course this was no great disappointment to those two silent, determined young men. "We are not circus performers," they said. "Our aim is to advance the science of aviation." And advance it they did. Their experiments continued, and in 1904 they made a record of three miles in 5 minutes 27 seconds. The next year, 1905, they made a record flight of 24.20 miles and remained in the air 38 minutes 13 seconds at heights of from 75 to 100 feet.