the progressive motion of a bird, or other winged animal, in the air.

The parts of birds chiefly concerned in flying are the wings and tail; by the first, the bird sustains and wafts himself along; and by the second, he is assisted, in ascending and descending, to keep his body poised and upright, and to obviate the vacillations thereof.

It is by the size and strength of the pectoral muscles, that birds are so well disposed for quick, strong, and continued flying. These muscles, which in men are scarcely a tenth part of the muscles of the body, in birds exceed and outweigh all the other muscles taken together; upon which Mr Willoughby makes this reflection, that if it be possible for a man to fly, his wings must be so contrived and adapted, that he may make use of his legs, and not his arms, in managing them.

The tail, Messrs Willoughby, Ray, and many others, imagine to be principally employed 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 inclination 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 disposed horizontally, and preserves the same situation whatever way forever the bird turns. In effect, as a vessel is turned about on its centre of gravity to the 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 inclination of their head and neck; which altering the course of gravity, the bird will proceed in a new 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 continued lamina. Being now raised a little above the horizon, and vibrating the wings with great force and velocity perpendicularly 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 continue to be in equilibrio, the bird will remain suspended in the same place; for the bird only ascends so long as the arch of air the wing describes 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 velocity as it is struck withal, there will be no resistance, and consequently the bird can never mount. Birds never fly upwards in a perpendicular line, but always in a parabola. In a direct ascent, the natural and artificial tendency would oppose and destroy each other, so that the progress would be very slow. In a direct ascent they would aid one another, so that the fall would be too precipitate.

Artificial FLYING, that attempted by men, by the assistance of mechanics.

The art of flying has been attempted by several persons in all ages. The Leucadians, out of 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 the fall.

Francis Bacon, who lived near 500 years ago, not only affirms the art of flying possible, but affirms us, that he himself knew how to make an engine wherein a man fitting 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. The secret consisted in a couple of large thin hollow copper globes, exhausted of air; which being much lighter than air, would sustain a chair whereon a person might sit. Father Francisco Lana, in his Prodromo, proposes the same thing as his own thoughts. He computes, that a round vessel of plate brass, 14 feet in diameter, weighing three ounces the square foot, will only weigh 1848 ounces; whereas a quantity of air of the same bulk will weigh 2153½ ounces; so that the globe will not only be sustained in the air, but will carry with it a weight of 373½ ounces; and by increasing the bulk of the globe, without increasing the thickness of the metal, he adds, a vessel might be made to carry a much greater weight.—But the fallacy is obvious: a globe of the dimensions he describes, Dr Hook shows, would not sustain the pressure of the air, but be crushed inwards. Besides, in whatever ratio the bulk of the globe were increased, in the same must the thickness of the metal, and consequently the weight be increased: so that there would be no advantage in such augmentation. See AEROSTATION.

The same author describes an engine for flying, invented by the Sieur Beffier, a smith of Sable, in the county of Maine. Vid. Philosoph. Collect. No. 1. The philosophers of King Charles the second's reign were mightily busied about this art. The famous Bishop Wilkins was so confident 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.

FLYING Bridge. See BRIDGE.

FLYING Fish, a name given to several species of fish, which, by means of long fins, can keep themselves out of the water for some time. See EXOCETUS, ICHTHYOLOGY Index.

FLYING Pinion, is part of a clock, having a fly or fan whereby to gather air, and so bridle the rapidity of the clock's motion, when the weight descends in the striking part.