242 



AEKONAUTICS. 



shall elude the air during the up stroke, it is necessary to 

 make it valvular, as shown at fig. 125, p. 241. 



This wing, as the figure indicates, is composed of numerous 

 narrow segments {fff), so arranged that the air, when the 

 wing is made to vibrate, opens or separates them at the 

 beginning of the up stroke, and closes or brings them together 

 at the beginning of the down stroke. 



The time and power required for opening and closing the 

 segments is comparatively trifling, owing to their extreme 

 narrowness and extreme lightness. The space, moreover^ 

 through which they pass in performing their valvular action 

 is exceedingly small. The wing under observation is flexible 

 and elastic throughout, and resembles in its general features 

 the other wings described. 



I have also constructed a wing which is self-acting in 

 another sense. This consists of two parts — the one part 

 being made of an elastic reed, which tapers towards the ex- 

 tremity; the other of a flexible sail. To the reed, which 

 corresponds to the anterior mxargin of the wing, delicate 

 tapering reeds are fixed at right angles ; the principal and 

 subordinate reeds being arranged on the same plane. The 

 flexible sail is attached to the under surface of the principal 

 reed, and is stifl'er at its insertion than towards its free mar- 

 gin. When the wing is made to ascend, the sail, because of 

 the pressure exercised upon its upper surface by the air, 

 assumes a very oblique position, so that the resistance ex- 

 perienced by it during the up stroke is very slight. When, 

 however, the wing descends, the sail instantly flaps in an 

 upward direction, the subordinate reeds never permitting its 

 posterior or free margin to rise above its anterior or fixed 

 margin. The under surface of the wing consequently descends 

 in such a manner as to present a nearly flat surface to the earth. 

 It experiences much resistance from the air during the down 

 stroke^ the amount of buoyancy thus furnished being very 

 considerable. The above form of wing is more effective 

 during the down stroke than during the up one. It, however, 

 elevates and propels during both, the forward travel being 

 greatest during the down stroke. 



Compound TFave Wing of the Autlior, — In order to render 



