4 



ANIMAL LOCOMOTION. 



artificial flight is absolutely necessary to it. This statement 

 is quite opposed to the commonly received opinion, but is 

 nevertheless true. No bird is lighter than the air, and no 

 machine constructed to navigate it should aim at being specifi- 

 cally lighter. What is wanted is a reasonable but not cumbrous 

 amount of weight, and a duplicate (in principle if not in prac- 

 tice) of those structures and movements which enable insectf^, 

 bats, and birds to fly. Until the structure and uses of wings 

 are understood, the way of " an eagle in the air " must of ne- 

 cessity remain a mystery. The subject of flight has never, 

 until quite recently, been investigated systematically or 

 rationally, and, as a result, very little is known of the laws 

 which regulate it. If these laws were understood, and we 

 were in possession of trustworthy data for our guidance in 

 devising artificial pinions, the formidable Gordian knot of 

 flight, there is reason to believe, could be readily untied. 



That artificial flight is a possible thing is proved beyond 

 doubt — 1st, by the fact that flight is a natural movement; 

 and 2d, because the natural movements of walking and swim- 

 ming have already been successfully imitated. 



The very obvious bearing which natural movements have 

 upon artificial ones, and the relation which exists between 

 organic and inorganic movements, invest our subject with a 

 peculiar interest. 



It is the blending of natural and artificial progression in 

 theory and practice which gives to the one and the other its 

 chief charm. The history of artificial progression is essen- 

 tially that of natural progression. The same laws regulate 

 and determine both. The wheel of the locomotive and the 

 screw of the steam-ship apparently greatly diff*er from the 

 limb of the quadruped, the fin of the fish, and the wing of 

 the bird ; but, as I shall show in the sequel, the curves which 

 go to form the wheel and the screw are found in the travelling 

 surfaces of all animals, whether they be limbs (furnished with 

 feet), or fins, or wings. 



It is a remarkable circumstance that the undulation or 

 wave made by the wing of an insect, bat, or bird, when those 

 animals are fixed or hovering before an object, and when they 

 are flying, corresponds in a marked manner with the track 



