450 



A HISTORY OF 



mon feathers only in their size being larger, 

 and also from their springing from the deeper 

 part of the skin, their shafts lying almost close 

 to the bone. The beards of these quills are 

 broad on one side and more narrow on the 

 other, both which contribute to the progres- 

 sive motion of the bird, and the closeness of 

 the wing. The manner in which most birds 

 avail themselves of these, is first thus : they 

 quit the earth with a bound, in order to have 

 room for flapping with the wing ; when they 

 have room for this, they strike the body of 

 air beneath the wing with a violent motion, 

 and with the whole under surface of the same; 

 but then to avoid striking the air with equal 

 violence on the upper side as they rise, the 

 wing is instantly contracted ; so that the ani- 

 mal rises by the impulse, till it spreads the 

 wing for a second blow. For this reason, 

 we always see birds choose to rise against 

 the wind, because they have thus a greater 

 body of air on the under than the upper side 

 of the wing. For these reasons also large 

 fowls do not rise easily ; both because they 

 have not sufficient room at first for the motion 

 of their wings, and because the body of air 

 does not lie so directly under the wing as 

 they rise. 



In order to move the wings, all birds are 

 furnished with two very strong pectoral mus- 

 cles, which lie on each side of the breast- 

 bone. The pectoral muscles of quadrupeds, 

 are trifling in comparison to those of birds. 

 In quadrupeds, as well as in man, the muscles 

 which move the thighs arid hinder parts of 

 the body are by far the strongest, while those 

 of the arms are feeble : but in birds, which 

 make use of their wings, the contrary obtains; 

 the pectoral muscles, that move the wings or 

 arms, are of enormous strength, while those 

 of the thighs are weak and slender. By 

 means of these, a bird can move its wings 

 with a degree of strength which, when com- 

 pared to the animal's size, is almost incredi- 

 ble. The flap of a swan's wing would break 

 a man's leg ; and a similar blow from an ea- 

 gle has been known to lay a man dead in an 

 instant. Such, consequently, is the force of 

 the wing, and such its lightness, as to be ini- 

 mitable by art. No machines, that human 

 skill can contrive, are capable of giving such 

 force to so light an apparatus. The art of 



flying, therefore, that has so often and so fruit- 

 lessly been sought after, must, it is feared, 

 forever be unattainable; since as man in- 

 creases the force of his flying machine, he 

 must be obliged to increase its weight also. 



In all birds, except nocturnal ones, the 

 head is smaller, and bears less proportion to 

 the body than in quadrupeds, that it may 

 more readily divide the air in flying, and 

 make way for the body, so as to render its 

 passage more easy. Their eyes also are 

 more flat and depressed than in quadrupeds; 

 a circle of small plates of bone, placed scale- 

 wise, under the outer coat of the organ, en- 

 compasses the pupil on each, to strengthen 

 and defend it from injuries. Beside this, 

 birds have a kind of skin, called the nicti- 

 tating membrane, with which, like a vail, 

 they can at pleasure cover their eyes, though 

 their eyelids continue open. This mem- 

 brane takes its rise from the greater or more 

 obtuse corner of the eye, and serves to wipe, 

 cleanse, and probably to moisten its surface. 

 The eyes, though they outwardly appear but 

 small, yet, separately, each almost equals the 

 brain ; whereas in man the brain is more than 

 twenty times larger than the orbit of the eye. 

 Nor is this organ in birds less adapted for 

 vision by a particular expansion of the optic 

 nerve, which renders the impressions olT ex- 

 ternal objects more vivid and distinct. 



From this conformation of the eye it follows, 

 that the sense of seeing in birds is infinitely 

 superior to that of other animals. Indeed 

 this piercing sight seems necessary to the 

 creature's support and safety. Were this 

 organ blunter, from the rapidity of the bird's 

 motion, it would be apt to strike against every' 

 object in its way ; and it could scarcely find 

 subsistence, unless possessed of a power to 

 discern its food from above with astonishing 

 sagacity. An hawk, for instance, perceives 

 a lark at a distance which neither men nor 

 dogs could spy ; a kite, from an almost im- 

 perceptible height in the clouds, darts down 

 on its prey with the most unerring aim. The 

 sight of birds, therefore, exceeds what we 

 know in most other animals, and excels them 

 both in strength and precision. 



All birds want the external ear standing 

 out from the head ; they are only furnished 

 I with holes that convey sounds to the audi- 



