CONTRIVANCE A NECESSITY. 159 



great amount of motion, or motion through a 

 long space, at the opposite or longer end. This 

 action requires indeed a very intense force to 

 be applied at the shorter end, but it applies 

 that force with immense advantage for the pur- 

 pose in view : because the motion which is trans- 

 mitted to the end of a long wing is a motion 

 acting at that point through a long space, and is 

 therefore equivalent to a very heavy weight lifted 

 through a short space at the end which is attached 

 to the body of the bird. Now this is precisely 

 what is required for the purpose of flight. The 

 body of a bird does not require to be much 

 lifted by each stroke of the wing. It only 

 requires to be sustained ; and when more than 

 this is needed — as when a bird first rises from 

 the ground, or from the sea, or when it ascends 

 rapidly in the air — greatly increased exertion 

 — in many cases, very violent exertion — is re- 

 quired.* And then it is to be remembered that 



* The Albatross, when rising from the sea, is described ("Ibis," 

 July 1865) as " stretching out his neck, and with great exertion of 

 his wings running along the top of the water for seventy or eighty 

 yards, until at last having got sufficient impetus, he tucks up his legs, 

 and is once more fairly launched into the air." The contrast here 



