FLYING AND FLYING-MACHINES. 333 



sion requires to acquire a swift forward motion. At 

 the same time it must be understood that I am not 

 questioning the undoubted fact that the downward beat 

 of a bird's wing is also capable of giving an upward 

 motion to the bird's body. The point to be specially 

 noticed is that when a bird is taking flight from level 

 ground, the wings are so used that the downward stroke 

 gives no perceptible upward motion. 



But since a horizontal velocity is thus effective, we 

 might be led to infer that the larger flying creatures, 

 which, cceteris paribus, travel more swiftly through the 

 air than the smaller, would require a smaller relative 

 extent of supporting surface. We are thus led to the 

 consideration of that point which has always been re- 

 garded as the great, or rather the insuperable difficulty, 

 in the way of man's attempts at flight, his capacity or 

 incapacity to carry the requisite extent of supporting 

 surface. We are led to inquire whether a smaller extent 

 of supporting surface than has hitherto been deemed 

 necessary may not suffice in the case of a man, and a for- 

 tiori in the case of a large and powerful flying-machine. 



The inference to which we have thus been led, is 

 found to accord perfectly with the observations which 

 have been made upon flying creatures of different 

 dimensions. It has been found that the supporting 

 surface of these creatures, whether insects, birds, or 

 "bats, by no means varies in proportion to their weight. 

 This is one of the most important results to which the 

 recent inquiries into the problem of flight have led; 

 and I believe that my readers cannot fail to be inte- 



