FLYING, the progressive motion of a bird, or other winged animal, in the li quid air. The parts of birds chiefly cerned in flying are the wings, by whit% they are sustained or wafted along. The tail, Messeurs Willoughby, Ray, and many others, imagine to be principally employ ed in steering and turning the body in the air, as a rudder : but Borelli has put it beyond all doubt, that this is the least use of it, which is chiefly to assist the bird in its ascent and descent in the air ; and to obviate the vacillations of the body and wings : for, as to turning to this or that side, it is performed by the wings, and inclinations of-the body, and but very little by the help of the tail. The flying of a bird, in effect, is quite a .different thing from the rowing of a vessel. Birds do not vibrate their wings towards the tail, as oars are struck towards the stern, but waft them downwards : nor does the tail of the bird cut the air at right angles, as the rudder does the water; but is dis posed horizontally, and preserves the same situation what way so ever the bird turns.
In effect, as a vessel is turned about on its centre of gravity right, by a brisk application of the oars to the left, so a bird, in beating the air with its right wing alone, towards the tail, will turn its fore part to the left. Thus pigeons, changing their course to the left, would labour it with their right wing, keeping the other almost at rest. Birds of a long neck alter their course by the inclinations of their head and neck, which altering the course of gravity, the bird will pro ceed in anew direction.
The manner of flying is thus : the bird first bends his legs, and springs with a violent leap from the ground ; then opens and expands the joints of his wings, so as to make a right line perpendicular to the sides of his body ; thus the wings, with all the feathers therein, constitute one con tinued lamina. Being now raised a little above the horizon, and vibrating the wings with great force and velocity per pendicularly against the subject air, that fluid resists those succussions, both from its natural inactivity and elasticity, by means of which the whole body of the bird is protruded. The resistance the air makes to the withdrawing of the wings, and consequently the progress of the bird, will be so much the greater, as the waft or stroke of the fan of the wing is longer : but as the force of the wing is continually diminished by this resistance, when the two forces come to be in equi librio, the bird will remain suspended ill.
the same place ; for the bird only ascends so long as the arch of air the wing de scribes makes a resistance equal to the excess of the specific gravity of the bird above the air. If the air, therefore, be so rare as to give way with the same velo city as it is struck withal, there will be no resistance, and consequently the bird can never mount. Birds never fly up wards in a perpendicular line, but always in a parabola. In a direct ascent, the na tural and artificial tendency would oppose and destroy each other, so that the pro gress would be very slow. In a direct descent, they would aid one another, so that the fall would be too precipitate. FLYINO, artificial, that attempted by men, by the assistance of mechanics. The art of flying has been attempted by several persons in all ages. The I.euca dians, out nf superstition, are reported to have had a custom of precipitating a man from a high cliff into the sea, first fixing feathers, variously expanded, round his body, in order to break his fall. Friar Bacon, who lived near five hundred years ago, not only affirms the art of flying pos sible, but assures us, that he himself knew how to make an engine, a man, sitting, might be able to convey himself through the air, like a bird ; and further adds, that there was then one who had tried it with success ; but this method, which consisted of a couple of large, thin, hollow copper globes, exhausted of the air, and sustaining a person who sat there on, Dr. Hook shows to be impracticable. The philosophers of K. Charles the se cond's reign were mightily busied about this art. Bishop Wilkins was so confi dent of success in it, that he says, he does not question but, in future ages, it will be as usual to hear a man call for his wings, when he is going a journey, as it is now to call for his boots.
The art of flying has, in some measure, been brought to bear in the construction and use of balloons. See /EnosrAriox.