In following the votaries of passive flight, as represented by Lilienthal and his school, we have overlooked the great dynamic aëroplane of Mr. Maxim, one of the most prominent aëroplane builders of that active period. Having in 1889 made elaborate experiments on the atmospheric resistance of sustaining surfaces, and on the thrust of screw propellers, he proceeded to build the gigantic aëroplane shown in Plate XVIII, the greatest flyer thus far known to history. It was a twin-screw multiplane mounted on a platform forty feet long by eight feet wide, and having four wheels running along a track eight feet wide and half a mile long. Above the rails of this track were guard rails to prevent the flyer from rising more than three inches during the tests. The whole machine weighed 3.5 tons, spread 5,500 square feet of surface, and, at a speed of 40 miles an hour, lifted more than a ton, in addition to the weight of the three men and 600 pounds of water. Its propelling plant comprised a naphtha tubular boiler, and a compound steam engine of 350 horse power actuating twin screws 17 feet 10 inches in diameter which gave a thrust approximating 2,000 pounds. These screws were made of American yellow pine, covered with canvas and painted, then smoothly sandpapered to reduce the friction; for Maxim, like certain French aviators, erroneously imagined that a polished surface has less air friction than a dead even surface. The framework was composed of seamless steel tubing stayed with steel wire. The aëroplane was to be steered right and left by a rudder, and up and down by horizontal planes, one fore, another aft, and its lateral stability was to be secured by side planes set at a dihedral angle. A meritorious feature for that day were the superposed arched surfaces whose framing was smoothly covered below and above by skillfully stretched fabric, causing the air to flow evenly without wasteful eddies. PLATE XVIII. [Illustration: MAXIM’S AËROPLANE. (Courtesy W. J. Hammer.)] [Illustration: LANGLEY’S LARGE AËROPLANE. (Courtesy Smithsonian Institution.)]