Mav 30, 1907J 



NA TURE 



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former spent a great amount of money and time in 

 valuable experiments, while the latter sacrificed his 

 life in advancing the science of gliding. 



Perhaps the most interesting portion of Dr. Bell's 

 address is the account of his own initial experiments 

 in the construction of an aerodrome. He has been at 

 work on this subject for many years, and so far 

 back as 1804 Langley visited him and witnessed some 

 of his experiments. 



The progress of his experiments is divided by 

 him into three stages, namely, the kite stage, the 

 motor-boat stage, and the free flying-machine rising 

 from the water. 



As the first of these is now complete, it is fully 

 described in this address, and indicates that a distinct 

 step in advance has been made. Dr. Bell's kite is 

 quite different from any other form. It is built up 

 of a great number of small structures or cells, all 

 alike in form and size. Each cell has the form of 

 a regular tetrahedron, and, as he says, " possesses 

 m a remarkable degree the properties of strength 

 and lightness." By connecting several of these 

 figures by their corners a very rigid structure is built 

 up, and the whole possesses the same properties of 



"WW 



strength and lightness inherent in the individual 

 cells themselves. 



The unit tetrahedral cell is bounded by four equal 

 triangular faces ; if two adjoining faces be covered 

 with some kite material, the result is a " winged 

 cell " resembling a pair of birds' wings with their 

 points raised upwards. Bv coupling four of these 

 unit cells together at their corners, a four-celled 

 structure is formed having itself the form of a tetra- 

 hedron, but with an empty space in the middle octa- 

 hedral in shape. If now four four-celled structures 

 be connected at their corners, a sixteen-cell structure 

 of tetrahedral form is formed (Fig. 2). Experience 

 has shown that when these structures are flown as 

 kites they exhibit remarkable automatic stability in 

 the air under varying conditions of wind. 



Up to the present time, the most stable form of 

 kite is that of the "box" or Hargrave type. Dr. 

 Bell is, however, of the opinion that his compound 

 tetrahedral structure is more stable even than this. 

 To make a comparison, he flew both kinds simul- 

 taneously in squally weather. Although the tetra- 

 hedral appeared to " shiver " when struck by a 

 sudden squall, the box kite " seemed to be liable to 



NO. 1 96 1, VOL. 76] 



a swaymg or tipping motion that would be exceed- 

 mgly dangerous in a structure of large size forming 

 part of a flying machine." 



The good behaviour of the former kite is due, as 

 he suggests, to the porous nature of the structure, 

 the squall passing right through between the covered 

 triangles, and lifting the other side of the kite as 

 well as the side first struck ; the blow is thus counter- 

 balanced before the kite has had tiine to upset. 



Although the horizontal aeroplane has always an 

 element of instability about it, it has, nevertheless, 

 greater lifting power than similar surfaces arranged 

 obliquely as in the tetrahedral construction. The 

 structure of winged cells is, however, the reverse. 



Fig. 3.— The Frost Kins in 

 supporting z 



flying in a ten-mile bri 

 I the flying ropes. 



being more stable when in the air, but deficient im 

 lifting power. There seems, however, no difficulty 

 in adding to the number of surfaces in the latter 

 construction in order to secure the desired lifting 

 power, while the condition of stability remains. 

 Further experiments have shown that the blank 

 spaces between the groups of winged cells can be 

 filled up with more cells; in fact, the cells can be 

 massed together " without marked injurious effects."' 

 Not only, therefore, is the structural strength 

 improved by this increase of size, but the lifting 

 power, which varies directly as the cube of the 

 dimensions, is increased (Fig. 3). 



The result of these kite experiments has been to 

 show that it is possible to build a structure of 

 moderate size, composed simply of these wingerf 



