FLYING. 



FLYING. 



ii 



quantity of force expended, if the weight of the body be called W, 

 is proportioned to */ W directly, and inversely as the square root 

 of the density of the air. 



There are varioiu methods of ascertaining that the air diminishes 

 in weight u we ascend in it. We know that the barometer falls when 

 taken to the top of an elevated hill ; and it is owing to this circum- 

 stance that the barometer is used to measure the heights of mountains. 

 The difference between the specific gravity of air and that of moat 

 animals is so great that there are but a few speciea amongst the whole 

 range of the Mammalia that are capable of flying, and these possess 

 very modified organs for that office. 



Attempts have been made to construct mechanism that would 

 enable man to propel himself in the air, and fly by means of his 

 muscular movements. This however is not likely ever to be effected, 

 in consequence of the great weight of his body with respect to that 

 of the air which it displaces. We know that when adventurous 

 persons have descended from the car of a balloon by means of a 

 parachute the surface of the latter which is presented to the wind 

 must be very great to prevent too rapid a descent. The unfortunate 

 termination of the life of Mr. Cocking arose from his not having 

 estimated more accurately the quantity of surface, and consequently 

 the strength of material that was necessary to prevent his falling 

 with too great velocity. Indeed we may dismiss the subject of a 

 man attempting to fly by the application of his muscular force to any 

 machinery at present known ; but seeing how extremely difficult it is 

 for any heavy body to be supported in the air, much more to fly, it 

 must be a matter of curiosity at least to inquire into the means 

 employed by animals which are naturally endowed with the power of 

 flight. 



Amongst the higher orders of Mammalia we find the Bats 

 possessing the greatest power of flight. The figure of the Bat 

 resembles in some degree that of a bird. In order to render it fit for 

 aerial progression the body is small, and the bones of the skeleton are 

 extremely light. The arms are long, and peculiarly constructed : the 

 fore arm has its motion restricted to flexion and extension, and cannot 

 rotate upon its long axis like that of a man. This gives the arm a 

 much greater degree of firmness during flight. The hand moves out- 

 wards and inwards horizontally, in the same manner as that of birds, 

 and cannot move upwards and downwards on the fore arm, which 

 would weaken the force of the wing in flight 



Fig. 1. Kalong But. 



The wing of the bat instead of being clothed, and having its surface 

 Increased with feathers, is composed of a membranous expansion, 

 panning from the neck to the tail In order to increase the surface of 

 the wing the bones of the fingers are very long ; the thumb is not 

 inclosed in the membrane, but lies in front of the wing, and termi- 

 nates by a strong hook for prehension. In the Bat the area of the 

 wings with respect to the weight of the body is very considerable. 

 Indeed the surface exceeds that of many birds. The muscles which 

 move the wings are extremely powerful, and these animals are enabled 

 to keep on the wing during a period of many hours. They appear 

 also to be endowed with an extraordinary and peculiar sensibility, 

 and can fly through an intricate labyrinth even when deprived of 

 sight The velocity of some species of the Bat tribe is very great 

 They chase and capture the insects on which they prey whilst on the 

 wing. 



There are some other species of Mammalia said to be capable of 

 flying, such as the Galeopitkecu$, or Flying Cat, and the Ptrromyi 

 Alpitu, or Flying Squirrel, but the notion is entirely without founda- 

 tion. They are certainly provided on each side with an expanded 

 membrane, as seen in Jig. 2, but these membranes have by no means 

 the turfsce requisite to enable them to fly ; neither are they capable 

 of moving like the wings of birds. They may be useful as parachutes, 

 to break their velocity of descent in falling or leaping from trees, 

 bat could never raise the body again from the ground into the air. 





Fig. 2. Flying Squirrel (Plrromyi Alpiniu). 



Most Birds are capable of flight, but their facility of flying varies 

 in different orders; and some, as the ostrich and cassowary, arc 

 devoid of the power of flight altogether ; but this defect is compen- 

 sated by their great speed in running. [RUNNING.] 



In the Ostrich and Cassowary the wings are very small and the body 

 extremely heavy, both which circumstances are unfavourable to flight; 

 but in birds which are endowed with great velocity the converse of 

 this is found, the body being very light and the surface of the wings 

 km. 



In order to adapt birds for flight the most refined mechanism has 

 been bestowed upon them. The skeleton is extremely light, and the 

 bones hollow and filled with air : the body is traversed by air- 

 cavities. The figure of a bird is such as to present a very small 

 amount of surface to the wind in the direction of its motion, so that 

 during its flight the animal is retarded as little as possible by the 

 resistance of the air. In birds of passage, such as woodcocks, &c., 

 which are known to cross the sea SOO miles at one flight, Sir George 

 Cayley found the length of the wing to be three and a half times 

 that of its greatest transverse section. The feathers keep the body 

 warm and tend to increase its surface without adding materially to 

 its weight The muscles which move the wings are very large and 

 endowed with great power. In some birds they are capable of con- 

 tinued action during many successive days. The figure of the wing 

 is nearly triangular, and the surface decreases as the distance increases 

 from the shoulder joint, which is the axis on which the wing moves. 

 (Fig. 8.) This figure of the wings is of great importance for rapid 

 flight, as it enables the muscles to move them with greater velocity 

 than they could do if the surface increased with the distance from 

 the body of the bird. The wing is also concave below and convex 

 above, so that the down stroke is much more effectual than the up 

 stroke. The bones of the fore arm and fingers which support the 

 wing are jointed, so that the wing unfolds itself outwards horizontally 

 after it has been raised in the air, as in the Bats ; and by these means 

 the wing is prevented from yielding, both in the up and down stroke, 

 to the resistance of the wind. The tail of the bird performs the 

 office of a rudder, and tends by iU elevation or depression to elevate 

 or depress the head. The elevation of the tail raises the head, and 

 vice verso. 



The mechanical effects of the tail have been demonstrated by 

 Borelli, and also by Mr. Bishop in the ' Cyclopaedia of Anatomy 

 and Physiology,' article ' Motion.' The tail is also turned obliquely 

 to alter the course of the bird, but the effects of this organ are not 

 very powerful in directing its path to the right or left. 



The number of flappings which any bird must make in order to 

 fly depends on the weight of the bird, the surface of the wings, and 

 the specific gravity of the atmosphere, the earth's gravity being 

 supposed constant at all heights to which any bird ascends. In most 

 of the smaller orders the wings move with very great rapidity, 



