mo 
BIRDS OF PASSAGE. 
O pillions of 
philosophers. 
Pliny, that 
jority of the British warblers, to the vicissitudes of tempera- 
ture which are annually experienced in this country, in com- 
mon with all other places at a distance from the equator. But 
their unanimity ends here 3 and, at this point, they split into 
two parties, who view the subject in very different lights. I 
intend to state the opinions of each in succession, beginning with 
those philosophers who appear to me to have the less degree of 
probability in their favour 3 or, to speak more properly, whose 
notions cannot be defended on their own principles, when 
these are carefully examined. 
Pliny is the oldest naturalist that I recollect, who maintains, 
that the swallow tribe, and many other birds, with whose 
they retire to winter quarters he was unacquainted, retire to caverns at the 
end of autumn, where they lie in a torpid state until the return 
of spring. Many moderns have embraced this idea 3 and 
they conclude from a familiar analogy, that the, sun, after 
making certain advances towards the north, recalls these 
sleepers from a lethargic state, to active existence, in the same 
manner, that he breaks the winter slumbers of the bat, the 
field-mouse, and the edge-hog 3 as well as of various reptiles, 
and insects inhabiting the temperate and frigid zones. This 
idea is captivating on account of its simplicity 5 and I, for one, 
would not refuse to adopt it, if the accuracy of the analogy, 
were but fairly established. But as this appears to be an im- 
possible task, I shall proceed immediately to state my objec- 
tions to the supposed constitutional connexion of the birds 
under consideration, and the animals with which they are 
compared. 
Those quadrupeds, reptiles, and insects, which pass the 
winter in a state of insensibility j may be recalled to sensation 
and action at pleasure, by the application of a gentle degree 
of warmth. This constitutional singularity of these animals, 
has induced philosophers to conclude unanimously, that the 
return of the sun in spring rouses them from a torpid condition, 
at a time when the benefits of the season are ready for their 
enjoyment. There is another circumstance, which gives some- 
thing more than plausibility to the supposition when it is pro- 
perly understood. For the animals in question take up their 
winter quarters, some of them in subterranean habitations, 
a little below the surface of the soil : others lodge in the cre- 
vices 
Analogy from 
torpid ani- 
mals. 
