Page:Popular Science Monthly Volume 28.djvu/19

Rh around in circles, occasionally elevating themselves by a few flaps of the wings, they glide down and up the aerial inclines without apparently any effort whatever. But a close observation will show that at every turn the angle of inclination of the wings is changed to meet the new conditions. There is continual movement with power—by the bird it is done instinctively, by our machine only through mechanism obeying a mind not nearly so well instructed.

The study of the flight of birds and insects has of late years received a great deal of attention, and, in a general way, the motions of the wings are fairly well understood. We could probably very closely imitate these motions, but the question at once arises, in doing so, would we be applying our power in the most effective way? While somewhat similar, the movement and construction of the wings of flying creatures vary considerably. What is best for a heavy body with short wings is by no means best for a light body with long wings; nor does a sea-bird, constantly on the wing, but perhaps not a rapid flier, fly in the same way as a pigeon or humming-bird; and, in any particular case, it does not necessarily follow that Nature has provided the most efficient apparatus; or, in other words, that the power the bird possesses could not be utilized more effectively. Nature can not always be trusted. We can study and understand her laws, but she does not pretend to apply them on economical principles. Fish and marine animals swim in a great variety of ways, they have all sorts of propelling arrangements, but there can be no doubt that a screw-propeller is vastly more efficient than any of them; and why should we try to copy the motions of a bird's wing any more than those of a fish's tail? The motions are very complicated in any case, and our machine, imitating them, would be complex and liable to get out of order. And one can not help thinking that we are about as likely to make a steam road-wagon by imitating the action of a horse, as we are to make a practicable flying-machine by copying the motions of a bird. The desired results can probably be obtained in a much more simple and effective way.

Still, the study of flying creatures has brought out many interesting and suggestive facts, and has given us, too, some encouragement.

In the first place, we notice that all birds are heavy, and that the expanse of wing generally diminishes in proportion to the increase of weight. The following is a table prepared by M, Lucy, showing this very clearly: