136 



POPULAR SCIENCE MONTHLY 



in construction, lighter in weight and oflEering less head resistance to 

 the wind. 



Diagram 2 shows a drawing of a kite built of two triangular cells. 

 The triangular cell needs bracing in one direction only, on its fiat 

 surfaces; in a transverse direction it is self-braced, so that internal 

 bracing, which causes head resistance, is unnecessary. 



By tying a number of kites built of triangular cells corner to corner, 

 as shown in Fig. 1, Dr. Bell was able to construct a giant kite, Fig. 

 2, in which the ratio of weight to wing surface is not much more than 

 that of the smaller kites of which it is composed. Combinations of 



Fig. 4. Floating Kite built of Tetrahedral Cells. 



triangular kites, however, must be arranged in two sets with a power- 

 ful connecting framework as shown in Fig. 2. The larger the two 

 sets, the farther apart must they be, and, therefore, the connecting 

 frame becomes exceedingly stout and lieavy. This connecting frame- 

 work is of course dead weight; it is a very serious handicap and soon 

 limits the size of kites that can be built of triangular cells. 



By his invention of the triangular cell Dr. Bell was able to build 

 larger kites than he had been able to build before. The old limit of 

 size was stretched considerably, but a limit remained none the less. 



The principal improvements of the triangular cell, greater lightness 

 and strength, are due to the cell being self-braced in a transverse direc- 

 tion, from side to side. Longitudinall3% fore and aft, it is, however, 

 very weak, like the box cell. Dr. Bell reasoned that a cell could be 

 made self-bracing in every direction by making it triangular in all 

 directions or tetrahedral in form. 



Accordingly a number of regular tetrahedral cells, Diagram 3, were 



