While Langley was building his great tandem monoplane, Wilbur and Orville Wright of Dayton, Ohio, were developing a biplane which was an improvement on the aërial glider of Chanute and Herring. This was to be their preliminary effort toward achieving continuous flight. Their first product, tried at Kitty Hawk, North Carolina, in the summer of 1900, is shown in Plate XIX. The chief points of departure from Chanute and Herring’s glider were (1) to place the rider prone on the lower surface, as first proposed and tried by Wenham, forty years’ previously; (2) to discard the vertical rudder; (3) to place the horizontal rudder forward, as done by Mattullath and Maxim; (4) to control the lateral balance by changing the impact angles of the wings, as recommended by the present writer in 1893. Of these four modifications the first was impractical for general use, though good for soaring and possibly racing; the second was unsatisfactory and later abandoned; the third was effective, and has been accepted by some aviators as an improvement, but rejected by others who prefer the rear[46] horizontal rudder; the fourth proved acceptable to them, as to various other inventors before and after them. With this glider they made a number of satisfactory flights. The front rudder and the torsional wings proved adequate to control the craft in sailing straight ahead down the Kill Devil sand hills, near Kitty Hawk, N. C. In this, as in all their machines to the present date, sled runners, fixed under the machine, as proposed by Ader and others, were used for launching and landing. With a surface of 165 square feet, they could glide down a slope of 9.5° at a speed of 25 to 30 miles an hour. This showed only a moderate efficiency, but it was a beginning. The glider used in the summer of 1901 was modeled after that of the previous year, but larger. It was 22 feet wide, 14 feet long, 6 feet high, spread 308 square feet, and weighed 108 pounds. With this a number of glides were made, of various lengths up to 400 feet. At a speed of 24 miles an hour gravity exerted on the aërial coaster 2½ tow line horse power, showing an efficiency nearly equal to that of Pilcher’s glider of 1897. In camp with the Wright brothers in 1901 was Mr. Chanute, the leading aëronautic expert in America. They thus had the advantage of his long experience, both as a student of aviation and a practical experimenter. With them were also two other specialists, Mr. E. C. Huffaker, an experienced aëronautical investigator, who had worked successively with Langley and Chanute; and Dr. G. A. Spratt, who had made some important investigations on the value of curved surfaces and the travel of the center of pressure with the varying angles of flight. The numerous animated conferences with these gentlemen were instructive and profitable. When the season closed the brothers returned home and experimented on curved surfaces to improve the efficiency of their glider. PLATE XIX.