FLIGHT. 247 



height : by spreading the tail and closing the wings 

 they cause the action of the air to predominate on 

 the hind part of the body, which directs the fore part 

 downwards, and leaves it entirely to the influence of 

 gravitation. 



"The tail may strengthen the action of the wing" 

 by moving towards the same side *." 



* Annales des Sciences for 1829, p. 502. 



