30 HISTORY OF 



such a great undertaking. It is probable that 

 the same instinct which governs all their other 

 actions, operates also here. They rather follow 

 the weather than the country; they steer only 

 from colder or warmer climates into those of an 

 opposite nature ; and finding the variations of 

 the air as they proceed in their favour, go on 

 till they find land to repose on. It cannot be 

 supposed that they have any memory of the 

 country where they might have spent a former 

 winter ; it cannot be supposed that they see the 

 country to which they travel from their height 

 in the air, since, though they mounted for miles, 

 the convexity of the globe would intercept their 

 view; it must therefore only be, that they go 

 on as they continue to perceive the atmosphere 

 more suitable to their present wants and disposi- 

 tions. 



All this seems to be pretty plain ; but there is 

 a circumstance attending the migration of swal- 

 lows which wraps this subject in great obscurity. 

 It is agreed on all hands, that they are seen mi- 

 grating into warmer climates, and that in amaz- 

 ing numbers, at the approach of the European 

 winter ; their return into Europe is also as well 

 attested about the beginning of summer. But we 

 have another account, which serves to prove that 

 numbers of them continue torpid here during the 

 winter, and, like bats, make their retreat into 

 old walls, the hollows of trees, or even sink into 

 the deepest lakes, and find security for the win- 

 ter season by remaining there in clusters at the 

 bottom. However this latter circumstance may 



