The machine on which the father of aërial gliding made his last flight is shown in Plate XVI. Of the hazardous nature of its construction Mr. Chanute thus writes: “The two surfaces were kept apart by two struts, or vertical posts, with a few guy wires, but the connecting joints were weak, and there was nothing like trussing. This eventually cost his most useful life. Two weeks before that distressing loss to science, Herr Wilhelm Kress, the distinguished and veteran aviator of Vienna, witnessed a number of glides by Lilienthal with his double-decked apparatus. He noticed that it was much wracked and wabbly, and wrote to me after the accident: ‘The connection of the wings and the steering arrangement were very bad and unreliable. I warned Herr Lilienthal very seriously. He promised me that he would soon put it in order, but I fear that he did not attend to it immediately.’” It will be observed that Lilienthal gave fair attention to the merits of both the monoplane and the biplane, the two familiar types in lively competition at the present hour. The first he found in Nature; the second he could have found in England, as the developments principally of Wenham and of Phillips. His example and prestige did much to promote the biplane; but he seems to have had no very decided preference for either. Though he found his biplane very satisfactory, he thought of returning to the monoplane. In April, 1896, he wrote:[27] “I am now engaged in constructing an apparatus in which the position of the wings can be changed during flight in such a way that the balancing is not effected by changing the position of the center of gravity of the body. In my opinion this means considerable progress, as it will increase the safety. This will probably cause me to give up again the double sailing surfaces, as it will do away with the necessity which led me to adopt them.” He thus seems to have studied the two types impartially, and to have invented a means for balancing the machine without shifting the center of mass. Lilienthal had given a powerful and permanent impulse to aviation, both by his writings and by his practical experience in the air. He first showed quantitatively the advantage of arched wings, by carefully derived tables of wind pressure; then he mounted the wings himself and taught the world, by bold and frequent flight, the art of aërial gravity sailing. The two remaining achievements, dynamic and soaring flight, he was to undertake as promptly as possible. If his life had been spared, no doubt he would have contributed much to the advancement of these arts, both by example and by direct effort; for he was in the prime of life, full of energy and daring, highly equipped, and ardently devoted to his favorite science. He began his studies in aviation at the age of thirteen and died at the age of forty-eight years.