GRAHAM BELL'S TETRAHEDRAL KITES. « 



In the June number of the National Geographic Mag-azine (Wash- 

 ington, D. C.) is a very interesting and instructive artick^, by Dr. Gra- 

 ham Bell on the tetrahedral principle in kite structure. The article 

 itself is so concise and depends so much upon illustrations, which are 

 reproduced to the number of 20 in the text and 70 in the Appendix, 

 that an effective representation of the contents in an article of smaller 

 dimensions is scarcely possible. Still the line of thought that runs 

 thi'ough the work which the article represents is so clear and so sug- 

 gestive that even an imperfect outline of it may be useful. Doctor 

 Bell indicates certain stages in the development of his ideas as "mile- 

 stones" of progress, and since the ultimate stage of the development 

 is the possibility of building up very large kite structures by combin- 

 ing unit cells in such a way that the proportion of weight to wing 

 area in the structure is nearly the same as that of the constituent cell 

 the successive stages are noteworthy. They sketch out in a most 

 interesting manner a reply to Newcomb's criticism of the limits of 

 application of the aeroplane based upon the argument that increase 

 of size means diminished efficiency because, for similar structures, the 

 weight varies as the cuIjc, while the area, upon which the lifting force 

 depends, varies as the square of the linear dimensions. 



The original stage, the ordinary kite, is a single plane structure. 

 The tirst step in adv^ance is the llargrave box kite, with its upper and 

 lower aeroplanes for its support and side planes for stability. To 

 stiffen the framework of tiie l)()x kite it nuist ])ebraci'd longitudinally 

 and transversely. Accordingly Graham lielTs development commences 

 by replacing the rectangular framework of the box kite hy a frame- 

 work of triangular section, which is by construction stiff so far as the 

 cross section is concerned. The inclined sides are by the vector prin- 

 ciple of resolution of forces regarded as equivalent to their geometri- 

 cal projections, and, in so far as the principle applies, the inclined 



« Reprinted from Nature, London, August 13, 1903, No. 1763, vol. 68, pp. 347-349. 

 SM 1903 13 183 



