AERONAUTICS. 



239 



which the wing is made to vibrate. This is proved by the 

 fact that insects, in order to fly, require, as a rule, to drive 

 their small wings with immense velocity. It is further 

 proved by the fact that the small humming-bird, in order to 

 keep itself stationary before a flower, requires to oscillate its 

 tiny wings with great rapidity, whereas the large humming- 

 bird {Patagona gigas)^ as was pointed out by Darwin, can 

 attain the same object by flapping its large wings with a very 

 slow and powerful movement. In the larger birds the move- 

 ments are slowed in proportion to the size, and more 

 especially in proportion to the length of the wing ; the cranes 

 and vultures moving the wings very leisurely, and the large 

 oceanic birds dispensing in a great measure with the flapping 

 of the wings, and trusting for progression and support to the 

 wings in the expanded position. 



Fm. 122. 



Fjg. 122. — Elastic spiral wing, which twists and untwists during its action, to 

 form a mobile helix or screw. This wing is made to vibrate by steam by a 

 direct piston action, and by a slight adjustment can be propelled vertically, 

 horizontally, or at any degree of obliquity. 



a, h. Anterior margin of wing, to which the neurse or ribs are affixed, c, d. Pos- 

 terior 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, iv) 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 antagonizes m. The alter- 

 nate stretching of the superior and inferior elastic bands contributes to the 

 continuous play of the wing, hy preventing dead points at the end of the down 

 and up strokes. The wing is free to move in a vertical and horizontal direc- 

 tion and at any degree of obliquity.— On(/Mia^. 



This leads me to conclude that very large wings may be 

 driven with a comparatively slow motion, a matter of great 

 importance in artificial flight secured by the flapping of 

 wings. 



