INTRODUCTION. 
3 
snow-flake is unable to remain suspended in the air ; 
that the still lighter thistle-down, when no longer 
supported by the breeze, has a tendency to fall to 
the ground ; and yet he is told, that there are 
tenants of the air, countless as those of earth and 
water; that some of considerable size and weight 
can journey on their way above the clouds, with a 
facility and speed far exceeding that of the swiftest- 
footed animal. He may, indeed, from observing 
that cork and light bodies, when plunged in water, 
rise to the surface, conceive the possible existence 
of a lighter substance than air, capable, by the same 
laws of nature, of rising above the earth. If a 
philosopher, he may even discover the inflammable 
and lighter air by which a balloon ascends, with 
the weight of a man attached ; but how shall he 
lift a substance heavier than the air ? and how guide 
its progress through the air ? Show him the weighty 
body of an Eagle or a Swan*, tell him their living 
history, and he may reasonably doubt your fact, and 
deny that these things could be. 
There is one difficulty in the use of wings that 
any one may ascertain for himself. Let him take 
the smallest sized boy’s kite by the narrow end, and 
wave it up and down at arm’s length ; he will 
instantly perceive how great is the resistance of the 
air, and how obvious the inability of his muscular 
strength to produce any thing like the rapid motion 
of a wing. And yet, in order to possess the powers 
of a bird, he must be able to construct and move 
artificial wings, in superficial extent, in some cases 
measuring several of such kites ; with the additional 
* The Wild Swan weighs 25 lbs. 
B 2 
