BIRDS IN GENERAL. 



449 



rises by a gentle swelling to its bulk, and 

 falls off in an expansive tail, that helps to 

 keep it buoyant, while the fore parts are 

 cleaving the air by their sharpness. From 

 this conformation, they have often been com- 

 pared to a ship making its way through wa- 

 ter; the trunk of the body answers to the 

 hold, the head to the prow, the tail to the 

 rudder, and the wings to the oars; from 

 whence the poets have adopted the meta- 

 phor of remigium alarum, when they describe 

 the wavy motion of a bird in flight. 



What we are called upon next to admire 

 in the external formation of birds is, the neat 

 position of the feathers, lying all one way, 

 answering at otice the purposes of warmth, 

 speed, and security. They mostly tend back- 

 ward, and are laid over one another in an 

 exact and regular order, armed with warm 

 and soft down next the body, and more strong- 

 ly fortified, and curiously closed externally, 

 to fence off the injuries of the weather. But, 

 lest the feathers should spoil by their violent 

 attrition against the air, or imbibe the mois- 

 ture of the atmosphere, the animal is furnish- 

 ed with a gland behind, containing a proper 

 quantity of oil, which can be pressed out by 

 the bird's bill, and laid smoothly over every 

 feather that wants to be dressed for the oc- 

 casion. This gland is situated on the rump, 

 and furnished with an opening or excretory 

 duct ; about which grows a small tuft of fea- 

 thers somewhat like a painter's pencil. When, 

 therefore, the feathers are shattered or rum- 

 pled, the bird, turning its head backwards, 

 with the bill catches hold of the gland, and, 

 pressing it, forces out the oily substance, with 

 which it anoints the disjoined parts of the 

 feathers; and drawing them out with great 

 assiduity, recomposes and places them in due 

 order; by which they unite more closely to- 

 ge'.her. Such poultry, however, as live for 

 the most part under cover, are not furnished 

 with so large a stock of this fluid, as those 

 birds that reside in the open air. The fea- 

 thers of a hen, for instance, are pervious to 

 every shower; on the contrary, swans, geese, 

 ducks, and all siich as nature has directed to 

 live upon the water, have their feathers dress- 

 ed with oil from the very first day of their 

 leaving the shell. Thus their stock of fluid 

 is equal to the necessity of its consumption. 



Their very flesh contracts a flavour from it, 

 which renders it in some so very rancid, as 

 to make it utterly unfit for food ; however, 

 though it injures the flesh, it improves the 

 feathers for all the domestic purposes to 

 which they are usually converted. 



Nor are the feathers with which birds are 

 covered less an object of admiration. The 

 shaft of every feather is made proportionably 

 strong ; but hollow below for strength and 

 lightness, and above filled with a pith to feed 

 the growth of the vane or beard that springs 

 from the shall of the feather on either side. 

 All these feathers are placed generally ac- 

 cording to their length and strength, so that 

 the largest and strongest feathers in flight 

 have the greatest share of duty. The vane 

 or beard of the feather is formed with equal 

 contrivance and care. It consists not of one 

 continued membrane ; because, if this were 

 broken, it could not easily be repaired ; but 

 it is composed of many layers, each some- 

 what in itself resembling a feather, and lying 

 against each other in close conjunction. To- 

 wards the shaft of the feather, these layers 

 are broad, and of a semicircular form, to 

 serve for strength, and for the closer graft- 

 ing them one against the other when in ac- 

 tion. Towards the outer part of the vane, 

 these layers grow slender and taper, to be 

 more light. On their under-side they are 

 thin and smooth, but their upper outer-edge 

 is parted into two hairy edges, each side ha- 

 ving a different sort of hairs, broad at bot- 

 tom, and slender and bearded above. By 

 this mechanism, the hooked beards of one 

 layer always lie next the straight beards of 

 the next, and by that means lock and hold 

 each other. 



The next object that comes under consi- 

 deration, in contemplating an animal that flies, 

 is the wing, the instrument by which this won- 

 derful progression is performed. In such 

 birds that fly, they are usually placed at that 

 part of the body which serves to poise the 

 whole, and support it in a fluid that at first 

 seems so much lighter than itself. They an- 

 swer to the fore legs in quadrupeds; and at 

 the extremity of this they hare a certain fin- 

 ger-like appendix, which is usually called the 

 bastard-wing. This instrument of flight is fur- 

 nished with quills, which differ from the com- 



