130 EELATION OF WING SURFACE TO WEIGHT. 



The fact that a win^i; surface of (>7 nun'- per gram enables the alba- 

 tross to sail, while the laughing gull recjuires 88(3 mm- for the same 

 purpose, and that the bustard gets along with (^i, while the sparrow 

 needs 200 and the fly 1,800 mm'-, can be explained onh^ on the supposi- 

 tion that the resistance of the air against moving wings is not directly 

 proportional to their size, but that in enlarging the wings the resisting 

 power of the air against them increases in a greater ratio than their 

 superficial dimensions. Knowing that the air requires an appreciable 

 time to yield to the pressure of the mo^'ing wing, and that the larger 

 the wing surface the greater the quantity of air displaced and the 

 greater the resistance of this compressed air to the subsequent wing 

 strokes which must act upon it, it is evident that this conclusion is 

 correct. 



There can therefore be no doubt that increasing size of body is 

 accompanied by a relative decrease of wing surface, and from this 

 fact we are able to draw interesting conclusions as to the size of the 

 wings a man would need to be able to fly. If we show the relation of 

 the weight to the size of the wing by the means of coordinates, con- 

 necting the points thus gained by a curve, and then extend this curve 

 as demanded by the relative weight of the heaviest animal, we secure 

 an approximate illustration of the wing size which such bodies would 

 require. Since the muscular power of a human being Avould by no 

 means suffice for flapping flight, it could only be a question of sailing- 

 flight in this case. I have therefore drawn a curve for sailing flyers 

 on the principle above indicated, from which the following is 

 deduced : 



70 kilograms, weight of body, would reciuire 32 innr of wing surface per gram. 

 80 kilograms, weight of bod3% would re(iuire 31 mnr of wiug surface per gram. 

 00 kilograms, weight of body, would require .30 mm" of wiug surface per gram. 

 100 kilograms, weight of body, would require 29.5 mui'' of wing surface per gram. 



According to the foregoing, if the combined weight of the body and 

 the mechanical flying apparatus amounts to 90 kilograms, in order 

 to sail like an albatross a man would require 1)0,000 times 80, or 

 2.700,000 mm'- of wing surface ; that is to say, two wings furnishing 

 together 2.7 square meters of surface. 



