PKOailESSION IN OR THROUGH THE AIR. 



125 



are slow; in small-winged ones comparatively very rapid. This 

 shows that flight may be attained by a heavy, powerful 

 animal with comparatively small wings, as well as by a 

 lighter one with enormously enlarged wings. While there is 

 apparently no fixed relation between the area of the wings 

 and the animal to be raised, there is, unless in the case of 

 sailing birds,^ an unvarying relation between the weight of 



Fig. 58.— TJnder-surface of large beetle (Goliathus micans), with deeply con- 

 cave and comparatively small wings (compare with butterfly, fig. 57), shows 

 that the ncrvures (r, d, e, /, n, n, n) of the wings of the beetle are arranged 

 along the anterior margins and tlironghoiit the substance of the wings 

 generally, very much as the bones of the arm, forearm, and hand, are in the 

 wings of the bat, to which they bear a very marked resemblance, both in 

 their shape and mode of action. The wings are folded upon themselves at 

 the point e during repose. Compare letters of this figure with similar letters 

 of fig. 17, p. ZQ.— Original. 



the animal, the area of its wings, and the number of oscilla- 

 tions made by them in a given time. The problem of flight 

 thus resolves itself into one of weight, power, velocity, and 

 small surfaces ; versus buoyancy, debility, diminished speed, 



1 In birds which skim, sail, or glide, the pinion is greatly elongated or 

 ribbon-shaped, and the weight of the body is made to operate upon the in- 

 clined planes formed by the wings, in such a manner that the bird when it 

 has once got fairly under weigh, is in a measure self-supporting. This is 

 especially the case when it is proceeding against a slight breeze— the wind 

 and the inclined x^lanes resulting from the upward inclination of the wings 

 reacting upon each other, with this very remarkable result, that the mass of 

 the bird moves steadily forwards in a more or less horizontal direction. 



