BIRDS. 5 



Mode of (tying. 



wards. That part of the force tending upwards, 

 is destroyed by the weight of the bird; and the 

 horizontal force serves to carry him forwards. 

 The stroke being completed, he moves up his 

 wings; which, being contracted, and having 

 their edges turned upwards, meet with very little 

 resistance from the air. When they are suffici- 

 ently elevated, he takes a second stroke down- 

 wards, and the impulse of the air again moves 

 him forward. These'successive strokes act only 

 as so many leaps taken in air. In turning to the 

 right or left, the bird strikes strongly with the 

 opposite wing, which impels him to the proper 

 side. The tail acts like the rudder of a ship ; 

 except that it moves him upwards or downwards, 

 instead of sideways. If the bird design to rise, 

 he raises his tail; and if to fall, he depresses it: 

 whilst he is in an horizontal position, it keeps 

 him steady. 



It has been remarked, that a bird, by spread- 

 ing his wings, can move horizontally in the air 

 for some time, without striking; because he has 

 acquired a sufficient velocity, and his wings 



" being parallel to the horizon, meet with a very 

 trifling resistance; and, when he begins to fall, 

 he can easily steer himself upwards by his tail, 



'till it be necessary to renew his motion by two 

 or three more strokes of his' wings. On alight- 

 ing, 'he expands his wings and tail full against 



' the air, that they may meet with all the resist- 

 ance possible. 



