[2] By the term aeroplane is meant a thin, light, expanded structure inclined at a slight upward angle to the horizon intended to float or rest upon the air, and calculated to afford a certain amount of support to any body attached to it.
[3] “On the Various Modes of Flight in relation to Aeronautics,” by J. Bell Pettigrew, Proc. Roy. Inst., 1867; “On the Mechanical Appliances by which Flight is attained in the Animal Kingdom,” by the same author, Trans. Linn. Soc., 1867.
[4] Revue des cours scientifiques de la France et de l’Étranger, 1869.
[5] The sphygmograph, as its name indicates, is a recording instrument. It consists of a smoked cylinder revolving by means of clock-work at a known speed, and a style or pen which inscribes its surface by scratching or brushing away the lampblack. The movements to be registered are transferred to the style or pen by one or more levers, and the pen in turn transfers them to the cylinder, where they appear as legible tracings. In registering the movements of the wings the tips and margins of the pinions were, by an ingenious modification, employed as the styles or pens. By this arrangement the different parts of the wings were made actually to record their own movements. As will be seen from this account, the figure-of-8 or wave theory of stationary and progressive flight has been made the subject of a rigorous experimentum crucis.
[6] This continuity of the down into the up stroke and the converse is greatly facilitated by the elastic ligaments at the root and in the substance of the wing. These assist in elevating, and, when necessary, in flexing and elevating it. They counteract in some measure what may be regarded as the dead weight of the wing, and are especially useful in giving it continuous play.
[7] “The importance of the twisted configuration or screw-like form cannot be over-estimated. That this shape is intimately associated with flight is apparent from the fact that the rowing feathers of the wing of the bird are every one of them distinctly spiral in their nature; in fact, one entire rowing feather is equivalent—morphologically and physiologically—to one entire insect wing. In the wing of the martin, where the bones of the pinion are short, and in some respects rudimentary, the primary and secondary feathers are greatly developed, and banked up in such a manner that the wing as a whole presents the same curves as those displayed by the insect’s wing, or by the wing of the eagle, where the bones, muscles and feathers have attained a maximum development. The conformation of the wing is such that it presents a waved appearance in every direction—the waves running longitudinally, transversely and obliquely. The greater portion of the wing may consequently be removed without essentially altering either its form or its functions. This is proved by making sections in various directions, and by finding that in some instances as much as two-thirds of the wing may be lopped off without materially impairing the power of flight.”—Trans. Roy. Soc. Edin. vol. xxvi. pp. 325, 326.
[8] “On the Various Modes of Flight in relation to Aeronautics,” Proc. Roy. Inst., 1867; “On the Mechanical Appliances by which Flight is attained in the Animal Kingdom,” Trans. Linn. Soc., 1867, 26.
[9] “On the Physiology of Wings; being an analysis of the movements by which flight is produced in the Insect, Bat and Bird,” Trans. Roy. Soc. Edin. vol. 26.
[10] The other forces which assist in elevating the wings are—(a) the elevator muscles of the wings, (b) the elastic properties of the wings, and (c) the reaction of the compressed air on the under surfaces of the wings.
[11] The wings of the albatross, when fully extended, measure across the back some 14 ft. They are exceedingly narrow, being sometimes under a foot in width.