NAVIGATING THE AIR 



birds and bats accomplish with such obvious facility. 

 And nothing is more certain than that attempts at aerial 

 flight have been made at various times since the begin- 

 ning of history. 



As with almost everything else in the matter of modem 

 scientific advancement, the mysterious writings of the 

 monk, Roger Bacon, are supposed to contain passages 

 to show that the worthy friar had an inkling of the secret 

 of air navigation. But he himself admits that he had 

 only a theoretical knowledge of the subject, and had 

 never seen a flying-machine of any kind in actual flight. 



Much more definite and tangible are the designs of 

 possible flying-machines still extant in the sketch-book 

 of Leonardo da Vinci, made in the fifteenth century. 

 From Leonardo's sketches it appears that the artist had 

 conceived the idea of constructing jointed wings to be 

 worked with strings and pulleys, the motive power to be 

 that of a man's arms and legs. It appears also that 

 later he had very definite ideas as to the possibilities 

 of an aerial screw, and he is believed to have constructed 

 one of these screws made on the same general plan as 

 that of the ordinary type of windmill in use at that time. 

 But nothing of practical importance came of any of 

 Leonardo's experiments. 



It is probable that his abandonment of the project of 

 flying by means of wings worked by muscular force was 

 due to the discovery that the strength of the muscles of 

 even the strongest man was relatively slight as compared 

 with the corresponding muscle of birds. Leonardo was 

 peculiarly capable of discerning this discrepancy in 

 strength, since he himself was one of the strongest men 



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