390 



BIRD 



for clothing, to protect the animal from the vicissitudes 

 of the weather, and feathers for flight. Both of these 

 are beautifully modified so as to suit the different 

 habits of the several species, and adapt them to the 

 climates and the elements in which they find their 

 food. 



Some other animals, as for instance the lepidop- 

 terous insects the butterflies and the moths have a 

 coat of feathers, or rather of fringed or feathery 

 scales ; but these have few or none of the characters 

 of true feathers, and in no case, except that of birds, 

 are feathers the instruments of flight. But still we 

 can, in the imperfect feathers of the lepidoptera, dis- 

 cover one of the uses of feathers in birds better than 

 we can perhaps do in the feathers of birds them- 

 selves, as in them it is conjoined with other uses. 

 The study of one animal often assists us in acquir- 

 ing a knowledge of another, especially when the 

 one contains a single part of that which is a com- 

 pound organ in another ; because by this means we 

 get an analysis of the living animal, which is far more 

 satisfactory than any that we could obtain by the 

 dissection of a dead one ; for we can, in the one 

 case, actually see the part of the organ in action, 

 whereas in the other we can only infer or guess at 

 the way in which it acts. 



Now, every one must have noticed, that bees, flies, 

 and all insects which have membranous or naked wings, 

 must keep those wings constantly in rapid motion 

 while they fly. The motion is often so rapid that the 

 wings cannot be seen, any further than by a sort of 

 tremulous motion in the air ; and the action of the 

 wings produces all that humming and buzzing among 

 flying insects, which makes the summer air so lively ; 

 for insects do not breathe by the mouth, and have no 

 organ of voice of any description. The action of 

 those naked wings upon the air must be very con- 

 siderable ; because when a common blue-bottle fly 

 (musca vomitoria) alights on the window, and marches 

 along one of the dusty bars of the frame, winnowing 

 the air with its wings, in a vain attempt to escape 

 through the glass, it stirs the dust more in proportion 

 than a coach and six driving rapidly along a dry 

 road on a hot summer's day. Insects with wings of 

 this description cannot hover, or lean on the air with 

 still and expanded wing. 



But the lepidoptera, especially the butterflies, do 

 hover about, and rest on the air, and wheel in various 

 directions, with very little apparent motion of the 

 wings ; and when they do move them, it is done 

 much more slowly than the motion of the naked 

 wing, in proportion to the rate of progressive motion. 

 These lepidopterous wings also move in silence, or 

 when they are brought into such rapid action as to 

 produce a sort of noise, it is a low and muffled rustle, 

 and does not ring out, so that the largest butterfly or 

 moth gets along much more silently than the gnat. 

 We may add, as a farther instance of the same kind, 

 that the bats (see BAT for the particulars, and in that 

 article will be found some of the points of difference 

 between bats and birds), when they fly, are obliged to 

 winnow the air with their flying membranes, some- 

 thing in the same way as naked winged insects, 

 though the flight of bats, unless when they are agi- 

 tated, is comparatively noiseless. So also those 

 reptiles which fly by means of membranous appen- 

 dages, are obliged to flutter these very much in pro- 

 portion to the rate of their progressive motion. 



Now the difference of action in these two textures 



of wings in the other classes of animals, shows us 

 the advantages which birds derive from their fea- 

 thery covering and feathery organs of flight. These 

 feathers, even to the minutest fibre on the plumes or 

 necks, are tubular, consisting of only a thin film of 

 solid matter, filled with air within, though strength- 

 ened by partitions of cellular substance, more or less 

 close together, according to the strain which the 

 feathers have to bear. From the mode in which the 

 feathers, and all their parts, are laid upon the bird, 

 it presents a smooth surface upwards and forwards, 

 so that the animal can move in either of these direc- 

 tions, with very little resistance from the friction of 

 the air. When it moves in either of them, the resist- 

 ance of friction does not increase so rapidly as the 

 rate of motion ; because the pressure smooths the 

 feathers, and causes the air to take less hold on them. 

 This property, which arises in part from the texture 

 of the upper surface of the feathers, but chiefly from 

 the way in which they are formed and placed, is of 

 equal service to birds when they must perch, or 

 otherwise remain at rest so as to abide the blast, as 

 when they fly exposed to it. Perching or flying, when 

 a bird is in the wind it always faces the current ; and 

 thus offers the least resistance both by its form and 

 its feathers. 



When, however, the leathers are taken in tin- 

 opposite directions, they offer as much increase of 

 resistance as they offer diminution when they are 

 taken above or in front. The wings are always more 

 or less hollow on the under sides, and they take hold 

 on the air by millions of fibres ; so that a bird with 

 its flying feathers on the stretch, would fall much 

 more slowly than one would suppose from the differ- 

 ence between its specific gravity and that of the air. 



The resistance which all the feathers on the body 

 of the bird offer to motion backwards is still greater ; 

 and it increases with the force which tends to move 

 the animal in that direction. The instant that it 

 begins to be so driven backwards as that a current 

 against its body is produced, the points of the feathers 

 rise, and take the wind with so many fibres that the 

 resistance is very similar to that made by a scaly 

 fish, when one attempts to draw one of these by the 

 tail; and every one who has angled, and accidentally 

 caught even a common trout in that way, knows that 

 an ounce weight is as difficult to land when so hooked 

 as a pound weight is when hooked by the head. 

 But the feathers of birds rise much more in propor- 

 tion than the free edges of the scales upon any fish ; 

 and they are every way as well formed for " holding 

 on" in the air, as those are for holding on in the 

 water. Thus the bird may be said to resist motion 

 backwards in the air, by throwing out the point of 

 each feather like the " fluke" of an anchor. 



And all this curious complexity of structure is 

 necessary for enabling the bird to perform those 

 motions which, in the case of an "air-bird," or one 

 which is much on the wing, and on it in all weather?, 

 is absolutely necessary. We are so much in the habit 

 of seeing birds fly, and they fly with such apparent 

 ease, that we are apt to overlook the many mechanical 

 difficulties that have to be overcome by their organi- 

 sation. But when attempts have been made by men 

 to construct flying apparatus, or even to accomplish 

 the apparently much simpler object of directing a 

 balloon, which floats buoyantly without any effort, 

 because it is filled with gas specifically lighter than 

 the atmosphere, the attempters, notwithstanding all 



