Ixxviii 
INTRODUCTION. 
muscles, as v»"ell as the expanse of feather, the hollowness of the bones, 
and lightness of the bodies of birds, and the air-cells within them, contri- 
butes greatly to rapidity of motion,®^ and birds that move their wings 
One of the translators of Bufifon, in a note at the end of the first volume of Birds, com- 
bats the opinion, that lightness of feather, and hollowness of the bones of birds, are among 
the causes of their rapid flight. He laughs at the doctrine as absurd, and yet, in the same breath, 
pronounces a theory as unphilosophical as ridiculous. The rapid flight of birds,” says he, 
results wholly from the prodigious power exerted by their large pectoral muscles.” This evi- 
dently is untrue; strip a bird of its plumage, and what would be its rapidity of flight? The 
pectoral muscles of the Ostrich are of enormous size and strength, and yet it is not buoyant in the 
atmosphere ; because nature has denied to it the flag-feathers of the wing. The pectoral muscles of 
the Bat are weak, and but little stronger than those of the Mouse, yet the one flits through the 
atmosphere, while the other by no exertions can mount into the air ; deprive the former of its mem- 
branous wing, it grovels on the earth, and is imm.ediately rendered incapable of flight, and yet its 
pectoral muscles remain. This strange theory is supported by positions equally ill-founded. 
Birds do not use their utmost exertions to overcome the resistance of the air; the Kingfisher often 
darts along, through a considerable space, by the force of one impulse of its wing ; and, by its 
buoyancy, the Hawk remains suspended in perfect stillness. Nor is it more correct, that those 
birds which have the longest necks, and consequently make the most acute angle between their 
shoulders and their bills, fly the fastest. The Swift, the Swallow, the Goatsucker, the Pigeon, 
and the Hawk kind, are most rapid in flight, and yet are not remarkable for length of neck ; but 
they possess a vast expansion of wing, with pectoral muscles of immense strength. On the other 
hand, the Water-rail, the Heron, the Bittern, the Water-hen, and the Land-rail, are formed with 
long necks, and yet their action on the wing is awkward, graceless, and tardy. The fact is, that 
many means conspire to produce rapidity of flight ; the specific gravity of birds, arising from the 
hollowness of their bones, and lightness of their feathers, the smallness and figure of their bodies, 
the expansion of their wings and tail, the length of the flag-feathers, and the closeness of their 
union, the thickness of their coverts, the elasticity and number of their internal air-cells, and the 
immense strength of their pectoral muscles. It is from a combination of powers, and not from a 
single one alone, that they acquire celerity ; without strong pectoral muscles, their wings would 
be useless ; without flag-feathers, these muscles would be of no effect in flight ; and without a 
proportional lightness of body, both the muscles and the wings would move in fruitless effort. As 
some of the propositions, offered to support this truly fanciful opinion, are built on calculations, 
perhaps the best mode to overset them is to place figures against figures in the scale. Assuming 
as a fact, according to the translator’s assertion, that the specific gravity of quadrupeds is nine 
hundred times greater than air; yet it does not follow, that an equal quantity of superficial matter 
