LANGLEY— LEFFMANtf. 159 



Attempts have been made to credit Da Vinci with the anticipation 

 of the modern aeroplane, but there is nothing in his essay which can 

 justify this claim. He made a study of the flight of birds, but his in- 

 ferences were not correct in some important respects, and while we 

 may give him credit for scientific method, it is apparent that he 

 " thought of " rather than " thought out " the problem of human 

 flight. Langley does not appear to have been acquainted with Da 

 Vinci's work, at least it is not quoted in any of his writings that I 

 have consulted, and in the article in the ninth edition of the Ency- 

 clopedia Britannica, which is given among his references, there is no 

 mention of Da Vinci's investigations, but these are briefly noted in 

 the eleventh edition (article on " Flight and Flying"). 



Claims have been made for many experimenters and investigators, 

 as having made flights with small machines, but definite data have 

 rarely been furnished, and it is probable that Langley is justified in 

 his claim that until the experiments in May, 1896 — to be later de- 

 scribed — no true flight of a heavier-than-air machine had been made. 



Machines based on the principle that Da Vinci discussed have been 

 built and operated by several investigators. These have been mostly 

 " gliders," enabling the person to make a slow, inclined descent from 

 a high point, but not conferring the power of rising from the ground 

 or alighting at a given place at a considerable distance from the 

 starting point. A glider of this type was constructed by Otto Lilien- 

 thal, and operated many times in the year 1896. He was killed by 

 the upsetting of his machine in a gust. Percy Pilcher made many 

 such flights in 1899, but also lost his life in an accident. Octave 

 Chanute, however, made over a thousand flights without injury to 

 himself. These operators sometimes made their flight by running 

 the machine, or having it pulled, against the wind and thus rising 

 from the ground much the same way as a kite is flown. It is obvious, 

 however, that these machines do not solve the problem of flying in 

 its important practical applications. It is also obvious that modern 

 flying machines, whether the dirigible balloon or the aeroplane, do 

 not act wholly on the principles of flight by the bird or insect. 



It is interesting to note that in animals the ratio of wing area to 

 weight diminishes as the weight increases. Thus, according to the 

 Encyclopedia Britannica, the wing area of the dragon fly is, in pro- 

 portion to its weight, nearly 25 times that of the pigeon. 



Langley began his investigations in 1887 at the Allegheny Ob- 

 servatory. At that time he was not aware that any other investigator 

 had accomplished anything along the lines that he was working, but 

 he subsequently found out that A. Penaud, an ingenious French 

 mechanician, had made in 1872, a machine about 20 inches long 

 resembling some of the simpler modern aeroplanes, using twisted 

 rubber as a motive power. He had described this in a journal called 



