On the physiology of wings : being an analysis of the movements by which flight is produced in the insect, bat and bird / by James Bell Pettigrew; communicated by Professor Turner.

  • Pettigrew, James Bell, 1834-1908
Date:
[1871]
Catalogue details

Licence: Public Domain Mark

Credit: On the physiology of wings : being an analysis of the movements by which flight is produced in the insect, bat and bird / by James Bell Pettigrew; communicated by Professor Turner. Source: Wellcome Collection.

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    and backwards during flexion. The wing during its vibration descends farther below the body than it rises above it. This is necessary for elevating purposes. The distal portion of the posterior margin of the wing of the insect is twisted in a downward and forward direction at the end of the down stroke, whereas, at the end of the up stroke it is twisted downwards and backwards. The proximal portion of the posterior margin always assumes a reverse position to that occupied by the distal portion, so that the posterior and anterior margins of the wing are not in the same plane, and in certain situations the two margins appear to cross each other. What is here said of the insect’s wing applies equally to the wings of the bat and bird. The wing during its vibrations twists and untwists, so that it acts as a reversing reciprocating screw. The wing is consequently a screw structurally and functionally. The blur or impression produced on the eye by the rapidly oscillating wing is twisted upon itself, and resembles the blade of an ordinary screw propeller. The twisted configuration of the wing and its screwing action are due to the presence of figure-of-8 looped curves on its anterior and posterior margins; these curves, when the wing is vibrating, re¬ versing and reciprocating in such a manner as to make the wing change form in all its parts. The curves in question are produced to a great extent by vital movements, independently alike of the elas¬ ticity of the wing and the reaction of the air. They can, however, be produced by the latter agencies likewise. The change and reversal of the curves occurring on the anterior and posterior margins cause the different portions of the wing to strike at various angles during the down and up strokes. The angles which the different parts of the wing make with the horizon are greatest towards the root, and least towards the tip of the wing. The angles are, in fact, adjusted to the speed at which the different portions of the wing travel—a large angle with a low speed giving the same amount of buoying and propelling power as a small angle with a high speed, The speed attained by the tip of the wing is always very much higher than that attained by those portions nearer the root—-the