128 



RELATION OF WING SURFACE TO WEIGHT. 



terfly has 11,()00. Careful observation shows, however, that in the main 

 the variation of this ratio depends on the size of the animal, or, stated in 

 general terms, the Avings are relatively larger the smaller and lighter 

 the animal to which they belong. It is shown also that the variations 

 from the general rule depend on the fact that the mode of flight is dif- 

 ferent in different animals. Some fl^'ing creatures overcome weight by 

 the rapid movement of their wings; others, especially at the beginning 

 of a stroke, take advantage of the internal atmospheric currents, and 

 use the enormous resistance of the air for their purpose. The first 

 class, to which the sjiarrow^ and the honeybee belong, may be desig- 

 nated as flapping flyers, and the last class, of which the albatross and 

 the sea eagle are examples, as sailing flyers. These extreme types of 

 the so-called flapping and sailing flyers are connected by an unbroken 

 chain of flying creatures, not all of which are so exclusively either 

 flappers or sailers as the birds just named. 



As might be expected, the flapping flyers have comparatively small 

 wings, which move swiftly by the aid of powerful muscles, while the 

 Avings of the sailers are moved by Aveaker muscles and more slowly. 

 If Ave take these tAvo classes into consideration separately, as in the 

 following tables, it is clearly shoAvn that the Aving surface increases 

 with decreasing Aveight of body. 



Flappers. 



Animal. 



Weight. 



Wing sur- 

 face to 1 

 gram 

 weight. 



Bustard . . . 

 Pheasant . . 

 Partridge.. 

 Sparrow . . . 

 Bumblebee 

 Honeybee . 

 House fly . - 

 Gnat 



Grams. 

 9,600 

 1,000 

 320 

 28 

 .44 

 .074 

 .01 

 .003 



Mm"- 



62 



88 

 105 

 200 

 2:^4 

 538 

 1,800 

 10. (KX) 



Sailers. 



Animal. 



Albatross 



Sea eagle 



Stork 



Silver gull 



Sparrow hawk 



Laughing gull 



Virgin dragon fly . 

 Lemon butterfly.. 



