645 



FLYING. 



FLYING. 



846 



indeed far too great to enable us to count them by the eye. The 

 winga of the diminutive and beautiful Hummiug-Bird oscillate with 

 sufficient rapidity to emit a humming sound ; hence its name. If 

 we can be satisfied that it is the number of flappings of the wings 

 which determines the pitch of the sound produced, we have a ready 

 method of ascertaining the number made in a given time, because 

 we can easily find in any work on acoustics how many oscillations are 

 necessary to produce the required tone. 



Fig. 3. The Great Ibijuu. 



The velocity with which any bird moves depends on the number of 

 flappings made by the wing in a unit of time, each flapping being 

 supposed to constitute one elevation and one depression of the wing. 

 It is estimated by M. Chabrier that the swallow expends as much 

 force merely to sustain itself in the air as would be sufficient to raise 

 its own weight 27'5 feet per second, and that its number of flappings 

 is about 15 per second. This estimate of the number of flappings is 

 however obviously greater than the bird employs; and notwith- 

 standing all the care and attention which M. Chabrier has bestowed 

 on the subject it is found that birds fly with much less expenditure 

 of muscular force than would appear to be necessary by mathematical 

 analysis.* 



Fig. 4. Humming-Bird. 



The velocity of some birds is very considerable. It has been gaid 

 that the Eider-Duck can fly 90 miles in an hour, and the Hawk 150 



* Sir George Cavley bai estimated that n force equivalent to onc-hovsc 

 power (mining 550 lb. one foot high in a second), if applied to appropriate 

 machinery, would sustain 115 lb. in the air. This however he considers 

 only tn approximate value, but perhapt not far from the truth. 



miles in the same time : there is however reason to suspect the 

 accuracy of these accounts. With regard to the Pigeon the case is 

 different. It is well known that these birds are trained to transmit 

 intelligence on special occasions in which great speed is required ; and 

 their velocity has in consequence been more accurately taken. Some 

 years ago two trained pigeons were started from Brighton at the 

 same time : one arrived in London in 70 minutes, the other in 78 

 minutes. Now, if we estimate the distance traversed by the birds in 

 question at 49 miles, it follows, by the rule of three, that the bird 

 which accomplished the journey in 70 minutes travelled at the rate 

 of 42 miles per hour, and the other at that of 38 miles; and it is 

 probable that the former is about the maximum velocity of the 

 Pigeon. It appears that in general pigeons make about 23 flappings 

 of the wing in 5 seconds. The Rook, which has a large surface of 

 wings, makes from about 10 to 15 effective strokes in a second. 



Some birds, the Lark for instance, ascend vertically in a right line 

 into the air to such heights as to become quite invisible, during which 

 movement they pour out their well-known joyous song, so pleasing to 

 the ear in consequence of its peculiar melody and purity of tone. 

 The warbling of this bird is distinctly heard even when the little 

 sougster itself appears in the zenith (owing to its great altitude) as a 

 mere speck. 



" Hark 1 hark ! the lark at Heaven's gate sings ! " Cymbcline. 



When birds poise themselves in one position in the air, their wings 

 oscillate in very small arcs compared with the arc through which they 

 sweep when in rapid motion. 



Many of the small, and indeed some of the larger birds, such for 

 example as the Woodpecker, move from one place to another by a 

 series of jerks, produced by three or four strokes of the wings made 

 in rapid succession ; immediately after which they close their wings, 

 whilst the body is forced forwards like a projectile, iu the path of a 

 parabolic curve. Of all known birds the Great Condor of South 

 America appeal's to have the greatest power on the wing. It is said 

 to be capable of elevating sheep and other animals into the air, and 

 of carrying them to the mountains to feed upon them at leisure. 

 The greatest weight it is capable of supporting in the air is not 

 accurately known, but it is doubtless very considerable. 



Fishes being adapted by their structure to move and respire in the 

 dense fluid of seas and rivers, are not constituted for flying. There 

 appear to be only two species of fish endowed with the power of 

 suspending themselves above the surface of the water; namely, the 

 VaclyUfternt, and the E.cocelus, or Flying-Fish. 



Fig. 5. Flying-Fish (Ejcocelusf. 



In the Kxocelia we observe that the pectoral fins assimilate very 

 nearly in figure, situation, and dimensions to the wings of birds ; 

 and if, with the velocity and inclination of the latter, they possessed 

 the power of oscillation, there seems to be no reason why they should 

 not keep in the air as long as they could respire in that medium. 

 But this does not appear to be the case. Their motions have been 

 observed by Mr. Bennett, who states that he never saw them sustain 

 themselves in the air for a longer period than about 30 seconds, and 

 that they made no vibratory movements of the fins. According to 

 Captain Basil Hall, their longest flight is about 200 yards ; and they 

 have been known to raise themselves as high as 20 feet above the 

 surface of the water. From these statements an estimate may be 

 made of the amount of force required to project the body into the 

 air to such an amazing height and distance. At least it must be 

 concluded that the muscular force employed is very great. 



Amongst the numerous tribes of Insects, there are vast multitudes 

 endowed with the power of flight. Now, although the mechanical 

 principles on which this power depends are the same as those in 

 birds, yet there is a considerable difference in the mechanism 

 employed to effect their aerial progression. 



The bodies of insects are traversed by air-tubes, which render 

 them light and buoyant. The jointed structure ot their frame 

 enables the animal to curve, shorten, or elongate the body on itself. 

 The wings present various forms (jig. 6, a, b, c, d, ,/), which exert 

 a material influence on the velocity and mode of their flight. : 

 well known that some insects are provided with one pair of wings, 

 and others with two. If we examine the surface of the wings, we 

 perceive cords, which are composed of hollow tubes passing across 

 the disc; these are called neurw, and when filled with fluid, confer 



