228 The National Geographic Magazine 



markable result is undoubtedly correct. 

 His conclusion, however, is open to 

 question, because he has drawn a gen- 

 eral conclusion from restricted premises. 

 He says : 



" Let us make two flying-machines exactly 

 alike, only make one on double the scale of the 

 other in all its dimensions. We all know that 

 the volume, and therefore the weight, of two 

 similar bodies are proportional to the cubes of 

 their dimensions. The cube of two is eight : 

 hence the large machine will have eight times 

 the weight of the other. But surfaces are as the 

 squares of the dimensions. The square of two 

 is four. The heavier machine will therefore 

 expose only four times the wing surface to the 

 air, and so will have a distinct disadvantage in 

 the ratio of efficiency to weight." 



a giant kite that should lift a man — 

 upon the model of the Hargrave box 

 kite. When the kite was constructed 

 with two cells, each about the size of a 

 small room, it was found that it would 

 take a hurricane to raise it into the air. 

 The kite proved to be not only incom- 

 petent to carry a load equivalent to the 

 weight of a man, but it could not even 

 raise itself in an ordinary breeze in which 

 smaller kites upon the same model flew 

 perfectly well. I have no doubt that 

 other investigators also have fallen into 

 the error of supposing that large struct- 

 ures would "necessarily be capable of 

 flight, because exact models of them, 



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FIG. 17 — THE AERODROME KITE 



Professor Newcomb shows that where 

 two flying- machines — or kites, for that 

 matter — are exactly alike, only differing 

 in the scale of their dimensions, the 

 ratio of weight to supporting surface 

 is greater in the larger than the smaller, 

 increasing with each increase of dimen- 

 sions. From which he concludes that if 

 we make our structure large enough it 

 will be too heavy to fly. 



This is certainly true, so far as it goes, 

 and it accounts for mv failure to make 



made upon a smaller scale, have demon- 

 strated their ability to sustain them- 

 selves in the air. Professor Newcomb 

 has certainly conferred a benefit upon 

 investigators by so clearly pointing out 

 the fallacious nature of this assumption. 

 But Professor Newcomb's results are 

 probably only true when restricted to> 

 his premises. For models exactly alike, 

 only differing in the scale of their dimen- 

 sions, his conclusions are undoubtedly 

 sound ; but where larsre kites are formed 



