Summer Birds of Passage. 455 
temperature, which are annually experienced, 
wm this country, in common with all other 
places at a distance from the equator. But 
their unanimity ends here; 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, be- 
ginning with those philosophers, who ap- 
pear to me to have the less degree of proba- 
bility in their favour; or, to speak more pro- 
perly, whose notions cannot be defended on 
their own principles, when these are carefully 
examined. © 
Pliny is the oldest naturalist that I recol- 
lect, who maintains, that the swallow tribe, 
and many other birds, with whose winter 
quarters he was unacquainted, retire to ea- 
verns at the end of autumn, where they lie 
in a torpid state until the return of spring. 
Many moderns have embraced this idea; and 
they conclude from a familiar analogy, that 
the sun, after making certain advances to- 
wards the north, recalls these sleepers from a 
lethargic state, to active existence, in the 
same manner, that he breaks the winter slum- 
bers of the bat, the field-mouse, and the 
hedge-hog ; as well as of various reptiles, and 
insects inhabiting the temperate, and frigid 
zones, ‘This idea is captivating on account 
