INTRODUCTION. 
7 
eternal frost,* enjoy a serene sky and a bright sun, while the terres- 
trial animals remain involved in darkness, and exposed to all the 
fury of the tempest. In twenty-four hours it can change its climate, 
and sailing over different countries, it will form a picture exceeding 
the powers of the pencil or the imagination. The quadruped knows 
only the spot where it feeds, its valley, mountain, or plain; it has 
no conception of the expanse of surface, or of remote distances, and 
generally no desire to push forward its excursions beyond its im- 
mediate wants. Hence remote journeys and extensive migrations 
are as rare among quadrupeds, as they are frequent among birds. It 
is this desire, founded on their acquaintance with foreign countries, 
on the consciousness of their expeditious course, and on their fore- 
sight of the changes that will happen in the atmosphere, and the 
revolutions of seasons, that prompts them to retire together at the 
powerful suggestions of an unerring instinct. When their food 
begins to fail, or the cold and heat to incommode them, their in- 
nate feelings and latent powers urge them to seek the necessary 
remedy for the evils that threaten their being. The inquietude 
of the old is communicated to the young; and collecting in troops, 
by common consent, influenced by the same general wants, im- 
pressed with the approaching changes in the circumstances of their 
existence, they give way to the strong reveries of instinct, and wing 
their way over land and sea to some distant and better country. 
Comparing animals with each other, we soon perceive that smelly 
in general, is much more acute among the quadrupeds than among 
the birds. Even the pretended scent of the Vulture is imaginary, 
as he does not perceive the tainted carrion, on which he feeds, 
through a wicker basket, though its odor is as potent as in the 
open air. This choice also of decaying flesh, is probably regulated 
by his necessities, and the deficiency of his muscular powers to 
attack a living, or even tear in pieces a recent prey. The structure 
of the olfactory organ, in birds, is obviously inferior to that of quad- 
rupeds; the external nostrils are wanting, and those odors which 
might excite sensation have access only to the duct leading from the 
palate : and even in those, where the organ is disclosed, the nerves, 
which take their origin from it, are far from being so numerous, so 
large, or so expanded as in the quadrupeds. We may, therefore, 
regard touch in man, smell in the quadruped, and sight in birds, as 
* The mean heights of eternal frost, under the equator, and at the latitude of 30° 
and 60°, are respectively 15,507 ; 11,484, and 3,818 feet. 
