160 
NATURAL HISTORY 
again, when they were on the point of breaking out in 
open mutiny, the appearance of a flock of birds suppress- 
ed their murmurs, and calmed their apprehensions, and 
again they courted the favouring gales. It is worthy of 
remark, that Columbus embarked just in the proper sea- 
son for observing the flight of the passage birds to their 
winter retreats; which might be contemplated as a circum- 
stance, in no small degree propitious to his enterprize. 
All birds have near their tail a little bag, which con- 
tains oil. This, Nature has designed for the purpose of 
moistening their feathers. Geese, and in general, all 
water fowl, are furnished with two glands for the secre- 
tion of this oil; other birds have only one. In these 
glands are divers little cells, ending in two or three large 
ones, lying under the nipple of the oil bag. This nip- 
ple is perforated, and being pressed by the bird’s bill, 
emits its oil. 
In all birds we may observe the several parts adapted 
to their respective uses in the very best manner. In 
those that fly much, the wings are placed in such a man- 
ner, as to balance their bodies in the air, and give the 
swiftest progression possible. Otherwise they would reel, 
and fly unsteadily. But in those that are designed for 
swimming, the wings are placed out of the centre of 
gravity, nearer the head. Hence the necessity of stretch- 
ing out the head and neck in an extraordinary manner, 
which gives them that awkward appearance they exhibit 
in flying. 
All birds are furnished with feet as well as wings; be- 
cause there is no food, or at least not sufficient for them, 
to be always had in the air. But if there were, yet such 
birds could take no rest; for having no feet, they could 
not perch upon trees, and if they alighted on the ground, 
they could not raise themselves again: which birds that 
have short legs can hardly do. Besides, the use of legs 
is indispensable, in laying their eggs, sitting, hatching, 
and brooding their young. 
We shall close these remarks by a few brief observa- 
tions on the comparative structure of birds, with that of 
other animals. The parts peculiar to birds, are, the bill* 
