NATURAL HISTORY. 
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PART II. 
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BIRDS, 
I 
io THEIR GENERAL NATURE. 
WV HILE the forefts, the waters, and even the 
depths of the earth, have their refpective inhabitants, 
the air, which includes an immenfe fpace, too ele- 
wated for the powér of man to explore, is traverfed 
by innumerable beings. of variegated beauty, called 
birds ; which, in order to ‘facilitate their flight 
through thole expanfive regions, with a {wiftnefs to 
compenfate their want of {trength, are formed on the 
following general principles. 
Form..... The body of a bird, is made fharp in 
front, and, when on flightthrough its native element, 
it fwells gradually, until the tail is fully -expanded, 
which, with the’aid of the wings, ferves it not only 
as a buoy, but alfo as a rudder to direct its flight. 
_ Puiumace.....They are covered with feathers, 
~moit admirably adapted to the air they inhabit, being 
compoted of a quill, containing a confiderable quan- 
tity of air, and a fhaft, edged on each fide with a moit 
volatile fubftance, which, with the concavity of the 
wings, renders the body confiderably lighter than.the 
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