or disease, have been frequently found in the hollows of rocks on the sea
coasts, and even under water in this torpid state, from which they have
been revived by the warmth of a fire. This torpid state of swallows is
testified by innumerable evidences both of antient and modern names.
Aristotle speaking of the swallows says, "They pass into warmer climates in
winter, if such places are at no great distance; if they are, they bury
themselves in the climates where they dwell," (8. Hist. c. 16. See also
Derham's Phys. Theol. v. ii. p. 177.)

Hence their emigrations cannot depend on a _necessary_ instinct, as the
emigrations themselves are not _necessary_.

2. When the weather becomes cold, the swallows in the neighbourhood
assemble in large flocks; that is, the unexperienced attend those that have
before experienced the journey they are about to undertake: they are then
seen some time to hover on the coast, till there is calm whether, or a
wind, that suits the direction of their flight. Other birds of passage have
been drowned by thousands in the sea, or have settled on ships quite
exhausted with fatigue. And others, either by mistaking their course, or by
distress of weather, have arrived in countries where they were never seen
before: and thus are evidently subject to the same hazards that the human
species undergo, in the execution of their artificial purposes.

3. The same birds are emigrant from some countries and not so from others:
the swallows were seen at Goree in January by an ingenious philosopher of
my acquaintance, and he was told that they continued there all the year; as
the warmth of the climate was at all seasons sufficient for their own
constitutions, and for the production of the flies that supply them with
nourishment. Herodotus says, that in Libya, about the springs of the Nile,
the swallows continue all the year. (L. 2.)