CONTENTS xix 



PAGE 



§ 420. The Flight of Birds divisible into Four Kinds — Differences to be Noted between Flapping or Rowing 



Fhght, and Saihng or Swimming Flight . ... 1267 



§ 421. The Eegular and Irregular in Flight .... . 1270 



The Wing Acts as a True Kite both during the Down and Up Strokes 1272 



§§ 422-423. Analogy between the Wing and a Boy's Kite — Points of Difference to be Noted — The Angles formed 



by the Wing with the Horizon during its Vibrations ... . . . 1272-1273 



§§ 424-429. The Margins of the Wing thrown into Opposite Curves during Extension and Flexion — The Tip 

 of the Bird's and Bat's Wing describes an BlUpse — The Wing capable of Change of Form in all 

 its Parts — The Wing when made to Vibrate produces a Cross Pulsation — Compound Rotation of the 

 Wing — The Wing Oscillates unequally with Reference to a Given Line . . . 1275-1277 



§ 430. The Flight of the Sea-GuU as witnessed on the West Coast of Scotland . . ... 1277 



§§ 431-432. Analysis of the Movements of Extension and Flexion in the Wing of the Gannet — The Angles of 

 Inclination which the Under Surfaces of the Gannet's Wing make with the Horizon in Extension and 

 Flexion vary ...... . 1278-1279 



MEASUREMENTS, WEIGHTS, &c., OF THE GANNET AND HERON 



§ 433. Flight of the Gannet as witnessed at the Bass Rock, Firth of Forth, Scotland . . . 1280 



§§ 434-435. A Regulating Power necessary in Flight — The Wings at all Times thoroughly under Control 1281-1282 

 Analysis of the Down and Up Strokes of the Wing of the Bird in Flapping or Rowing Flight 1283 

 § 436. The Body is made to Ascend when the Wings Descend and vice versd . . 1285 



§ 437. The Natural Wing when Elevated and Depressed must move Forwards 1286 



§ 438. The Body and Wings move in Opposite Curves . . . ... 1287 



§ 439. Birds fly by causing their large, powerful Wings to act upon the Air as Kites ; the Air furnishing 

 a suitable Fulcrum for supporting and carrying them Upwards and Forwards — The Wings are Pro- 

 pelled by Voluntary well-directed Muscular Movements, aided by certain Elastic Structures which 

 contribute to the continued Vibrations of the Wings — In Fhght, Weight and Momentum play an 

 important Part . . . . . ... 1288 



§ 440. Lifting Capacity of Birds 1288 



§ 441. Mode of Ascending, Descending, Turning, &c. . 1289 



THE WINGS OF BATS 



§ 442. Where the Bat's Wing agrees with and differs from that of the Insect and Bird . 1291 



§ 443. The Bones of the Wing of the Bat — The Spiral Configuration of their Articular Surfaces . 1291 



§ 444. Extension and Flexion of the Wing of the Bat .... . 1291 



THE WINGS OF PTERODACTYLS {Extinct flying reptiles) 



§ 445. The Wings of Pterodactyls are Original Structures in the Sense that they formed part of the Animals 



when Created ... 1293 



§ 446. The Wings of Pterodactyls conform to the Requirements of Fhght, as witnessed in Insects, Birds, and 



Bats 1294 



§ 447. The Wings of Pterodactyls afford Examples of Extreme Modification for a Special Purpose . , 1294 



