INDEX. 



283 



Walking (man), 111 



(horse), 142 

 Wing (bird's) 



action downward and back- 



ward at each stroke, 235 



active and passive parts of, 



276 



ascent of, like action of boy's 



kite, 273 



analogy to human arm, 211 



at each revolution of, bird 



rises twice, 272 



change of plane in, 244, 



257 



compared to screw, 211 



curves in, 210 



depression of, elevates and 



carries forward the body, 

 269 



descent of, gives all motive 



force, 273 



duration of elevation and 



depression of, 228 



frequency of strokes of, 227 

 . Hartiugs on, 223 



instrument to show change 



in plane of, 258 



inclination of, changes gra- 



dually, 263 



M. de Lucy on, 222 



Louvrie', M. de, on angle of 



plane of bird's wing, 275 



movements of, 226 



ratio to weight, 222, 225 



Wing (birds') continued. 



re-action of movements of, 



on body, 264 

 of wild duck, 

 &c., 267 



trajectory of pigeon's, 255 

 Wing (insects') 



act as inclined planes, 200 



artificial representation of, 



198 



causes of movement of, 196 



changes in plane of, 190-204 



figure -of-8 movement of, 195 



flexible membrane of, 208 



flight instrument, illustrat- 



ing, 206 



frequency of movement of, 



181-185 



moves downward and for- 



ward, 197 



movements of, determined 



optically, 187 



propulsion of, from below 



upward and forward, 204 



shape of, 276 

 structure of, 196 



trajectory of (Or. Pettigrew), 



201 

 Work, mechanical, 60 



unit of, 16 



Z. 



Zootrope, 137 



Zuckung, shock of muscles, 30 



THE END. 



