Animal Locomotion; or, walking, swimming, and flying / With a dissertation on aëronautics

by James Bell Pettigrew

[109] Revue des Cours Scientifiques de la France et de l’Etranger. Mars 1869.

[110] It is clear from the above that Borelli did not know that the wings of birds strike forwards as well as downwards during the down stroke, and forwards as well as upwards during the up stroke. These points, as well as the twisting and untwisting figure-of-8 action of the wing, were first described by the author. Borelli seems to have been equally ignorant of the fact that the wings of insects vibrate in a more or less horizontal direction.

[111] “Reign of Law”—Good Words, 1865.

[112] “Reign of Law”—Good Words, February 1865, p. 128.

[113] History of British Birds. Lond. 1837, p. 43.

[114] “Méchanisme du vol chez les insectes. Comment se fait la propulsion,” by Professor E. J. Marey. Revue des Cours Scientifiques de la France et de l’Etranger, for 20th March 1869, p. 254.

[115] Revue des Cours Scientifiques de la France et de l’Etranger. 8vo. March 20, 1869.

[116] In sculling strictly speaking, it is the upper surface of the oar which is most effective; whereas in flying it is the under.

[117] Compare Marey’s description with that of Borelli, a translation of which I subjoin. “Let a bird be suspended in the air with its wings expanded, and first let the under surfaces (of the wings) be struck by the air ascending perpendicularly to the horizon with such a force that the bird gliding down is prevented from falling: I say that it (the bird) will be impelled with a horizontal forward motion, because the two osseous rods of the wings are able, owing to the strength of the muscles, and because of their hardness, to resist the force of the air, and therefore to retain the same form (literally extent, expansion), but the total breadth of the fan of each wing yields to the impulse of the air when the flexible feathers are permitted to rotate around the manubria or osseous axes, and hence it is necessary that the extremities of the wings approximate each other: wherefore the wings acquire the form of a wedge whose point is directed towards the tail of the bird, but whose surfaces are compressed on either side by the ascending air in such a manner that it is driven out in the direction of its base. Since, however, the wedge formed by the wings cannot move forward unless it carry the body of the bird along with it, it is evident that it (the wedge) gives place to the air impelling it, and therefore the bird flies forward in a horizontal direction. But now let the substratum of still air be struck by the fans (feathers) of the wings with a motion perpendicular to the horizon. Since the fans and sails of the wings acquire the form of a wedge, the point of which is turned towards the tail (of the bird), and since they suffer the same force and compression from the air, whether the vibrating wings strike the undisturbed air beneath, or whether, on the other hand, the expanded wings (the osseous axes remaining rigid) receive the percussion of the ascending air; in either case the flexible feathers yield to the impulse, and hence approximate each other, and thus the bird moves in a forward direction.”—De Motu Animalium, pars prima, prop. 196, 1685.

[118] The human wrist is so formed that if a wing be held in the hand at an upward angle of 45°, the hand can apply it to the air in a vertical or horizontal direction without difficulty. This arises from the power which the hand has of moving in an upward and downward direction, and from side to side with equal facility. The hand can also rotate on its long axis, so that it virtually represents all the movements of the wing at its root.