Tetrahedral Principle in Kite Structure 231 



3/i inch diameter) made an angle with 

 the horizon of about 45° when the rope 

 snapped under the strain. 



Tremendous oscillations of a pitching 

 character ensued ; but the kite was at 

 such an elevation when the accident 

 happened, that the oscillations had time 

 to die down before the kite reached the 

 ground, when it landed safely upon 

 even keel in an adjoining field and was 

 found to be quite uninjured by its rough 

 experience. 



Kites of this type have a much 

 greater lifting power than one would at 

 first sight suppose. The natural as- 

 sumption is that the winged superstruc- 

 ture alone supports the kite in the air, 

 and that the boat body and floats repre- 

 sent mere dead-load and head resistance. 

 But this is far from being the case. Boat- 

 shaped bodies having a V-shaped cross- 

 section are themselves capable of flight 

 and expose considerable surface to the 

 wind. I have successfully flown a boat 

 of this kind as a kite without any super- 

 structure whatever, and although it did 

 not fly well, it certainly supported itself 



in the air, thus demonstrating the fact 

 that the boat surface is an element of 

 support in compound structures like 

 those shown in figures 17 and 20. 



Of course the use of a tetrahedral cell 

 is not limited to the construction of a 

 framework for kites and flying -ma- 

 chines. It is applicable to any kind of 

 structure whatever in which it is de- 

 sirable to combine the qualities of 

 strength and lightness. Just as we can 

 build houses of all kinds out of bricks, 

 so we can build structures of all sorts 

 out of tetrahedral frames, and the struct- 

 ures can be so formed as to possess the 

 same qualities of strength and lightness 

 which are characteristic of the individ- 

 ual cells. I have already built a house, 

 a framework for a giant wind-break, 

 three or four boats, as well as several 

 forms of kites, out of these elements. 



It is not my object in this communi- 

 cation to describe the experiments that 

 have been made in my Nova Scotia lab- 

 oratory, but simply to bring to your at- 

 tention the importance of the tetrahedral 

 principle in kite construction. 



APPENDIX 



Copyright, ipoj, by the National Geographic Magazine 



Through the courtesy of Dr Bell the National Geographic Magazine 

 is able to present as an appendix to this article a series of some seventy illustra- 

 tions of experimental forms of kites and structures used by Dr Bell. The 

 illustrations were selected by the editor from several hundred pictures in Dr Bell's 

 notebooks. The pictures were taken and developed by Mr David George 

 McCurdy, the photographer of his laboratory, with the exception of Plate III, 

 which was taken by Mr F. Tracy Hubbard. The notes explaining the illustra- 

 tions were written by Dr Bell by request. 



