386 DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 



' In the gannet there is only 1 foot 1 square inch of wing for every 2 lbs. 

 4^ ounces of body. The gannet has, consequently, less than half of the wing 

 area of the heron. The gannet's wing is, however, a long narrow wing (that 

 of the heron is broad), extended transversely across the body in the direction 

 of its length; and this is found to be the most powerful form of wing — the 

 wings of the albatros, which measure 14 feet from tip to tip (and only one foot 

 across), elevating 18 lbs. without difficulty. If the wings of the gannet, which 

 have a superficial area of 3 feet 3 inches square, are capable of elevating 7 lbs., 

 while the wings of the heron, which have a superficial area of 4 feet 4 inches, 

 can only elevate 3 lbs., it is evident (seeing the wings of both are twisted 

 levers, and formed upon a common type) that the gannet's wing must be vibrated 

 with greater energy than the heron's wing; and this is actually the case. 

 The heron's wing, as I have stated (foot note to page 392), makes 60 down and 

 60 up strokes every minute ; whereas the wing of the gannet, when the bird is 

 flying in a straight line to or from its fishing ground, makes close upon 150 

 up and 150 down strokes during the same period. The wings of the divers 

 and other short- winged, heavy-bodied birds are urged at a much higher speed, 

 so that a comparatively small wing can be made to elevate a comparatively heavy 

 body, if the speed with which the wing is driven only be increased sufficiently.'"" 

 Flight, therefore, is a question of power, speed, and small surfaces versus 

 weight. While there is apparently no fixed relation between the area of the 

 wing and the animal to be raised, there is (unless in the case of sailing birds, 

 which have acquired momentum) an unvarying relation as to the weight to be 

 elevated and the number of oscillations ; so that the problem of flight would seem 

 to resolve itself into one of weight, power, velocity, and small surfaces, as against 

 comparative levity, debility, diminished speed, and extensive surfaces.! Ela- 

 borate measurements of wing area and minute calculations of speed can, con- 

 sequently, only determine the minimum of wing for elevating the maximum of 

 weight — flight being attainable within a comparatively wide range. That the 

 superficies of the wings destined to carry a certain weight may, and does vary, 

 is proved by the fact that large portions of the wings of insects and birds, as 

 I have pointed out,J may be removed without destroying or even impairing the 

 function of flight. In such cases the speed with which the wings are driven is in- 

 creased in the direct ratio of the mutilation. It is further proved by the ingenious 

 researches of M. de Lucy, who has shown, by careful measurements, that the 



* The grebes among birds and the beetles among insects furnish examples where small wings, 

 made to vibrate at high speeds, are capable of elevating great weights. 



t " On the Mechanism of Flight," by the Author, Trans. Linn. Soc, vol. xxvi. page 219. 



| Vide page 326 and foot-note to pages 361 and 362 of the present memoir, and pages 219, 220, 

 221, and 222 of my memoir "On the Mechanical Appliances by which Flight is Attained in the 

 Animal Kingdom," Trans. Linn. Society, vol. xxvi. 



