420 



BELL 



pound kite ; the two triangular surfaces, in their flying position, 

 resembling a pair of wings raised with their points upward, the 

 surfaces forming a dihedral angle. (A, Plate XIII.) Four of 

 these unit cells, connected together at their corners, form a four- 

 celled structure, having itself the form of a tetrahedron contain- 

 ing in the middle an empty space of octahedral form, equal in 

 volume to the four tetrahedral cells themselves. (B, Plate XIII.) 

 In my paper I showed that four of these four-celled structures 

 connected at their corners resulted in a sixteen-celled structure 

 of tetrahedral form, containing, in addition to the octahedral 

 spaces between the unit cells, a large central space equivalent 

 in volume to four of the four-celled structures. (C, Plate XIII.) 

 In a similar manner four of the sixteen-celled structures con- 

 nected together at their corners form a sixty-four-celled structure. 

 (D, Plate XIII. ) Four of the sixty-four-celled structures form a 

 two hundred and fifty-six-celled structure, etc., etc., and in 

 each of these cases an empty space exists in the center, equiva- 

 lent to half of the cubical contents of the whole structure, in 

 addition to spaces between the individual cells, and minor groups 

 of cells. 



Kites so formed, exhibit remarkable stability in the air under 

 varying conditions of wind, and I stated in my paper that the 

 kites which had the largest central spaces seemed to be the most 

 stable in the air. Of course these were the structures that were 

 composed of the largest number of unit cells ; and I now have 

 reason to believe that the automatic stability of these kites de- 

 pends more upon the number of unit cells than upon the pres- 

 ence of large empty space in the kites ; for I have found, upon 

 filling in these empty spaces with unit cells, that the flying 

 qualities of a large kite have been greatly improved. The 

 structure, so modified, seems to fly in as light a breeze as be- 

 fore but with greatly increased lifting power ; while the gain in 

 structural strength is enormous. 



I had hitherto supposed that if cells were placed directly be- 

 hind one another, without providing large spaces between them, 

 comparable to the space between the two cells of a Hargrave 

 box kite, the front cells would shield the others from the action 

 of the wind, and thus cause them to lose their efficiency ; but no 



