224 The National Geographic Magazine 



diminish with each increase in the size 

 of the compound kite. Unfortunately, 

 however, the conditions of stable flight 

 demand a considerable space between 

 the front and rear sets of cells (see 

 Fig. 6) ; and if we increase the diameter 



of our compound structure without in- 

 creasing the length of this space we in- 

 jure the flying qualities of our kite. 

 But every increase of this space in the 

 fore and aft direction involves 'a cor- 

 responding increase in the length of the 

 empty framework required to span it, 

 thus adding dead load to the kite and 

 increasing the ratio of weight to surface. 



the character shown at B to prevent 

 distortion under the action of the wind. 

 The necessary bracing, however, not 

 being in the way of the wind, does not 

 materially affect the head resistance of 

 the kite, and is only disadvantageous 

 by adding dead load, thus increasing 

 the ratio of weight to surface. 



THE TETRAHEDRAL CONSTRUCTION 

 OF KITES 



Passing over in silence multitudinous 

 experiments in kite construction carried 

 on in my Nova Scotia laboratory, I come 



fig. 9- 



-A. A TRIANGULAR CELL 

 B. A WINGED TETRAHEDRAL CELL 



to another conspicuous point of ad- 

 vance — another milestone of progress — 

 the adoption of the triangular construc- 

 tion in every direction (longitudinally as 

 well as transversely) ; and the clear 

 realization of the fundamental impor- 

 tance of the skeleton of a tetrahedron, 

 especially the regular tetrahedron, as 



Acute-angledtetrahedron Regular tetrahedron R, fe ht-antled tetrahedron. 



FIG. 10 — WINGED TETRAHEDRAL CELLS 



Obtuse-angled tetrahedron 



While kites with triangular cells are 

 strong in a transverse direction (from 

 side to side) , they are structurally weak 

 in the longitudinal direction (fore and 

 aft) , for in this direction the kite frames 

 are rectangular. 



Each side of the kite A, for example 

 (Fig. 8), requires diagonal bracing of 



an element of the structure or frame- 

 work of a kite or flying-machine. 



Consider the case of an ordinary trian- 

 gular cell A (Fig. 9) whose cross-section 

 is triangular laterally, but quadrangular 

 longitudinally. 



If now we make the longitudinal as 

 well as transverse cross-sections trian- 



