Vol. XIV, No. 6 



WASHINGTON 



June, 1903 



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THE TETRAHEDRAL PRINCIPLE IN KITE 



STRUCTURE* 



By Alexander Graham Bell 



President of the National Geographic Society 



Copyright, 1903, by the National Geographic Magazine 



IN 1899, at the April meeting, I made 

 a communication to the Academy 

 upon the subject of " Kites with 

 Radial Wings ; ' ' and some of the illus- 

 trations shown to the Academy at that 

 time were afterwards published in the 

 Monthly Weather Review. \ 



Since then I have been continuously 

 at work upon experiments relating to 

 kites. Why, I do not know, excepting 

 perhaps because of the intimate connec- 

 tion of the subject with the flying-ma- 

 chine problem. 



We are all of us interested in aerial 

 locomotion ; and I am sure that no one 

 who has observed with attention the 

 flight of birds can doubt for one mo- 

 ment the possibility of aerial flight by 

 bodies specifically heavier than the air. 

 In the words of an old writer, ' ' We 

 cannot consider as impossible that which 

 has already been accomplished." 



I have had the feeling that a properly 



constructed flying-machine should be 

 capable of being flown as a kite ; and, 

 conversely, that a properly constructed 

 kite should be capable of use as a fly- 

 ing-machine when driven by its own 

 propellers. I am not so sure, however, 

 of the truth of the former proposition 

 as I am of the latter. 



Given a kite, so shaped as to be suit- 

 able for the body of a flying-machine, 

 and so efficient that it will fly well in a 

 good breeze (say 20 miles an hour) when 

 loaded with a weight equivalent to that 

 of a man and engine ; then it seems to 

 me that this same kite, provided with 

 an actual engine and man in place of 

 the load, and driven by its own pro- 

 pellers at the rate of 20 miles an hour, 

 should be sustained in calm air as a fly- 

 ing-machine. So far as the pressure of 

 the air is concerned, it is surely imma- 

 terial whether the air moves against the 

 kite, or the kite against the air. 



*A communication made to the National Academy of Sciences in Washington, D. C 

 April 23, 1903, revised for publication in the National Geographic Magazine. 

 tSee Monthly Weather Review, April, 1S99, vol. xxvii, pp. 154-155, and plate xi 



