UNDER THE MAPLES 



the inclined surface of its body on the atmosphere 

 to counterbalance its gravity. The force to keep 

 up the momentum of a body moving in a horizontal 

 plane in the air (in which there is so little friction) 

 cannot be great, and this force is all that is wanted. 

 The movement of the neck and body of the condor, 

 we must suppose, is sufficient for this. However 

 this may be, it is truly wonderful and beautiful to 

 see so great a bird, hour after hour, without any 

 apparent exertion, wheeling and gliding over moun- 

 tain and river. 



The airplane has a propelling power in its motor, 

 and it shifts its wings to take advantage of the 

 currents. The buzzard and condor do the same 

 thing. They are living airplanes, and their power 

 is so evenly and subtly distributed and applied, 

 that the trick of it escapes the eye. But of course 

 they avail themselves of the lifting power of the 

 air-currents. 



All birds know how to use their wings to propel 

 themselves through the air, but the mechanism of 

 the act we may not be able to analyze. I do not 

 know how a butterfly propels itself against a breeze 

 with its quill-less wings, but we know that it does 

 do it. As its wings are neither convex nor concave, 

 like a bird's, one would think that the upward and 

 downward strokes would neutralize each other; 

 but they do not. Strong winds often carry them 

 out over large bodies of water; but such a master 



34 



