DK PETTIGREW ON THE PHYSIOLOGY OF WINGS. 



423 



It should be convex above and concave below, and slightly twisted upon 

 itself. 



It should be flexible and elastic throughout, and should twist and untwist 

 during its vibration, to produce figure of 8 curves along its margins and through- 

 out its substance. 



Such a wing is represented at figure 02. 



7 d 



Fig. 62/ 



If the wing is in more than one piece, joints and springs require to be added 

 to the body of the pinion. 



In making a wing in one piece on the model of the insect wing, such as that 

 shown at figure 62, I employ one or more tapering elastic reeds, which 

 arch from above downwards (a b) for the anterior margin. To this I add 

 tapering elastic reeds, which radiate towards the tip of the wing, and which 

 also arch from above downwards {g, h, i). These latter are so arranged that 

 they confer a certain amount of spirality upon the wing, the anterior (a b) and 

 posterior (cd) margins being arranged in different planes, so that they appear to 

 cross each other. I then add the covering of the wing, which may consist of 

 india-rubber, silk, tracing cloth, linen, or any similar substance. 



If the wing is large, I employ steel tubes, bent to the proper shape. In 

 some cases I secure additional strength by adding to the oblique ribs or stays 

 (g h i of figure 62) a series of very oblique stays, and another series of cross 

 stays, as shown at m and a, n, o, p, q of fig. 63, page 424. 



* Fig. 62. Elastic spiral wing, which twists and untwists during its action, to form a mobile helix or screw. This 

 wing is made to vibrate by a direct piston action, and by a slight adjustment can be propelled vertically, horizontally, 

 or at any degree of obliquity. 



a, b, Anterior margin of wing, to which the neurae or ribs are affixed, c, d, Posterior margin of wing crossing 

 anterior one. x, Ball and socket joint at root of wing, the wing being attached to the side of the cylinder by the socket. 

 t, Cylinder, r, r, Piston, with cross heads (w, w) and piston head (s). o, o, Stuffing boxes. e,f, Driving chains, m, 

 Superior elastic band, which assists in elevating the wing, n, Inferior elastic band, which antagonises m. The alternate 

 stretching of the superior and inferior elastic bands contributes to the continuous play of the wing, by preventing dead 

 points at the end of the down and up strokes. 



VOL. XXVI. PART II. 



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