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 gas 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 Ib. 

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