BIRD. 



407 



a tumble would be the probable, and broken bones j 

 or dislocatedjoints, the possible 1 , ami indeed the very 

 likely consequences. Thus we sue that in nature's '_ 

 mechanics, the contrivances by which purposes are 

 accomplished, are not only the best adapted for those 

 purposes, but. they are applied for the accomplish- 

 ment of them in the best manner, both for success in 

 the end and for safety to the instrument. 



This principle is one of the most difficult to carry 

 into complete, or even tolerable effect, in the whole 

 compass of human mechanics; but it is one which nature 

 invariably displays in all her structures, and in all 

 the varieties of their working. This must, however, 

 in the case of animals, and especially in that of pre- 

 datory animals, be considered true only as affects the i 

 animal to which the structure belongs : for as the j 

 prey and the preyer are part of the general system of j 

 nature, and as such made for each other, the perfec- 

 tion of the system requires that the prey should be 

 taken as much at a disadvantage to itself as there is 

 advantage on the part of the preyer. 



And this is well exemplified in all birds which 

 strike, or otherwise capture their prey on the wing, 

 and more especially in the jer-falcon, which may be 

 said to perform that operation in most magnificent 

 style, at least in so far as the slaughter of one bird by 

 another can be considered magnificent. The jer- 

 falcon, at forward flight, and without the excitement 

 produced by the joint effects of hunger and the sight 

 of that which can appease it, can cleave the air at the 

 rate of at least one hundred miles in the hour ; but 

 when she works herself to the top of her bent, and 

 then rushes forward in the tempest of her impetuosity, 

 her motion is double, triple, nay, probably more than 

 five, or even ten times that rate ; so that if she could 

 hold on with the same speed, she would keep pace 

 with the motion of the earth on its axis, even at the 

 equator, where it is about a thousand miles an hour, 

 and outstrip it by much in her own northern latitudes. 



Hard as are the bones, and tough as are the tendons 

 and ligaments in the foot of the jer-falcon, they could 

 not hold directly against so terrible a rush as this ; and 

 were she to strike against a solid and fixed substance, she 

 would be dashed to pieces by her own velocity would 

 perish through the very excess of her own strength. 



But this violent motion of the falcon, the circum- 

 stances under which it is exerted, and the organisation 

 by means of which it is performed, are all admirably 

 adapted to each other. The stroke of the falcon, 

 unlike the spring of the beasts of prey, or even the 

 stoop of the eagle, and the other predatory birds 

 which kill their prey upon the ground, does not, in 

 itself, arrest the violence of her motion ; for when 

 she misses, if she hawks at nocking birds, as she 

 often does, she dashes onwards, and strikes again ; 

 whereas the lion and the tiger must pause and crouch 

 before they can take a second spring, and the eagle 

 must regain her height before she make a second 

 stoop. Thus the prey of these animals, if not cap- 

 tured at the first attempt, has a chance of escape 

 much greater than the prey of the jer-falcon. 



When we consider the circumstances under which 

 this gallant bird strikes, and the force of the stroke, 

 which is sufficient to fracture a wing, sever a head, 

 or crush the chest and burst open the body of a 

 bird, we can easily see that the great velocity of 

 the rush is necessary for effecting the natural purpose 

 of the bird ; and that, though the jer-falcon would 

 probably dash herself to pieces where she to exert all 



her energy in preying anywhere else than in the free 

 air, yet she is exactly the bird, above all others, for 

 that element. Her prey is of course escaping from 

 her with its best wing, though the agitation produced 

 by such a follower must of course render that wing 

 a little tremulous ; but still the motion of the prey 

 must be deducted from that of the falcon, in order to 

 get the true impetus with which the latter strikes. 

 Besides this, the bird has no resistance but that of the 

 all-clastic atmosphere, and the inertia arising from its 

 weight diminished by its motion ; and therefore a stroke 

 given with moderate velocity would have very little 

 effect upon it. But the speed of the falcon over the 

 speed of the prey furnishes the power ; and the in- 

 strument, as already mentioned, sustains no injury on 

 account of its position, and of the communication, 

 and consequent extinction of the shock upon it ; first, 

 in the elastic part of the falcon upon which it bears 

 for support ; and, secondly, in the air, against which 

 the entire body of the falcon would recoil if neces- 

 sary, as the smaller hawks may be seen to do when 

 they are flown at too heavy game. 



Far from the least remarkable part of the skeleton 

 of this model of a flyer is the sternum. It will be 

 observed, on looking back to the sketch, that the 

 forks in the posterior portions of that bone are not 

 only united by bony continuations, but that only 

 a small aperture is left in the place of each. The 

 keel, or central ridge of the sternum, is also remark- 

 ably elevated, and much produced at its anterior 

 extremity, so that its outline forms a complete arch. 

 We shall afterwards have to compare the sterna of 

 different genera with each other, and with their 

 several habits, as among the means of forming an 

 arrangement of the class, approaching at least to a 

 natural one. But as in that we must have some 

 model from which to start (the means of pro- 

 ceeding then being comparison, and comparison 

 not being an instrument of knowledge, unless one of 

 the subjects is known), and as the sternum of the 

 jer falcon is the one best adapted both for exceed- 

 ingly rapid and for long-continued flight, it is about 

 the best model that we can select. From the shape 

 of this bone, as well as from the general arrangement 

 of the skeleton, we can see that, though the legs are 

 rather strong in their bones, and the muscles by which 

 they are moved are rather powerful, yet that the 

 great strength of the bird is thrown into the anterior 

 part of the body. Here it is not a little remarkable 

 that this form of the body of a bird, while it admits 

 of the best organisation for flight, is also the best 

 one for being propelled through the air, or through 

 any other fluid, be the propelling force what it 

 may. When it is desirable to have a very fast- 

 sailing ship, which shall at the same time make the 

 closest course, or the least lee-way, and therefore get 

 through the water with the least strain from the 

 action of the wind, the shape which answers best 

 for the hull of such a ship is not unlike that of the jer- 

 falcon full at the bows, and narrowed away at the 

 stern, so as to make (he least wake or turbulence in the 

 water behind her. This coincidence of the shape of 

 birds which impel themselves through the air by the 

 energy of their own muscles, with that of ships which 

 are impelled through the water by the action of the 

 wind on their sails, is nota little remarkable ; and it is 

 one of those cases which shows that there is a lesson 

 for our instruction, and an example for our imitation, 

 so far as we can imitate, in all the operations of nature. 



