180 AEEIAL NAVIGATION. 



the hitter, and upon this the school of Lilienthal and his followers is 

 founded. 



Otto Lilienthal was a German engineer of great originalit}' and 

 talent, who, after making very valuable researches, assisted by his 

 brother, published a book in 1SS!», Der Vogelflug als Grundlage der 

 Fliegekunst, which it is very desira])lo to have translated and pub- 

 lished for the benefit of English investigators. Then, putting his 

 theories to the test of practice, he built, from 18*U to I-Six;, a number 

 of aeroplane machines with which ho diligently trained himself in 

 gliding flight, using gravity for a motive power, by starting from hill- 

 sides. He grew exceedingly expert, and made, it is said, more than 

 2,000 flights, until one rueful da}' (August !», iSiH)) he was upset and 

 killed by a wind gust, probablj^ in conse(|uence of having allowed his 

 apparatus to get out of order. 



He was followed })v ]\Ir. Tilcher, an English marine engineer, who 

 slighth^ improved the api)aratus, l>ut ^v•ho, after making many hundred 

 glides, was also upset and killed in October, 1899, through structural 

 weakness of his machine. 



The basis for the equilibrium of an apparatus gliding upon the air 

 being that the center of gravity shall l)c on the same vertical line as 

 the center of air pressure, ))oth Lilienthal and Pilcher reestablished 

 this condition l)y moving their bodily weight to the same extent that 

 the center of pressui'e varied through the turmoils of the wind. The 

 writer ventured to think this method erroneous, and proposed to 

 reverse it l)y causing the surfaces themselves to alter their position, so 

 as to bring the center of pressure back vertically over the center 

 of gravity. He began experimentally with man-carrying gliding 

 machines in June, 1896, and has since built six machines of Ave dif- 

 ferent t^'pes, with three of which several thousand glides have been 

 efl'ected without anv accidents. The first was a Lilienthal machine, in 

 order to test the known before passing to the unknown, and this was 

 discarded some six weeks before LilienthaTs sad accident. 



With three of the other machines favorable results were obtained. 

 The best were with the "two-surface" machine, equipped with an 

 elastic rudder attachment designed by Mr. Herring, and this was 

 described and figured in the Aeronautical Annual for 1897. 



Three years later Messrs. Wilbur and Orville Wright took up the 

 pro))lem afresh and have worked independently. These gentlemen 

 have placed the rudder in front, where it proves more efi'ective than 

 in the rear, and have placed the operator horizontall}^ on the machine, 

 thus diminishing by four-fifths the resistance of the man's body from 

 that which obtained with their predecessors. In 1900, 1901, 1902, and 

 1903 they made thousands of glides without accidents, and even suc- 

 ceeded in hovering in the air for a minute and more at a time. They 

 had obtained almost complete mastery over their apparatus before they 



