40 A HISTORY OP 



rind more ban sufficient plenty of food from the number of insects, 

 which swarm thereto an incredible degree. The days there are long; 

 and the beautiful meteorous nights afford them opportunity of collect- 

 ing so minute a food, which is probably of all other the most grateful. 

 We are not to be astonished, therefore, at the amazing number of 

 fowl that descend from these regions at the approach of winter ; num- 

 bers to which the army of Xerxes was but trifling in comparison ; and 

 which Linnaeus has observed for eight whole days and nights to cover 

 the surface of the river Calix. 



This migalion from the north usually begins in September, when 

 they quit their retreats, and disperse themselves over all the southern 

 parts of Europe. It is not unpleasing to observe the order of their 

 flight; they generally range themselves in a long line, or they some- 

 times make their march angularly, two lines uniting in the centre like 

 the letter V reversed. The bird which leads at the point seems to 

 cleave the air to facilitate the passage for those which are to follow. 

 When fatigued with this laborious station, it falls back into one of the 

 wings of the file, while another takes its place. With us they make 

 their appearance about the beginning of October, circulate first round 

 our shores, and, when compelled by severe frost, betake themselves to 

 our lakes and rivers. Some, indeed, of the web-footed fowl, of har- 

 dier constitutions than the rest, abide the rigours of their northern 

 climate the whole winter ; but when the cold reigns there with more 

 than usual seventy, they are obliged to seek for more southern skies. 

 They then repair with the rest for shelter to these kingdoms ; so that 

 the diver, the wild swan, and the swallow-tailed sheldrake, visit our 

 coasts but seldom, and that only when compelled by the severity oi 

 their winters at home. 



It has been often a subject ot astonishment, how animals, to all ap 

 pearance so dull and irrational, should perform such long journies; 

 should know whither to steer, and when to set out upon 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 intc 

 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 thc'ir 

 present wants and dispositions. 



All this seems to be pretty plain : but there is a circumstance at 

 tending the migration of swallows which wraps this subject in great 

 obscurity. It is agreed on all hands, that they are seen migrating into 

 warmer climates, and that in amazing numbers, at the approach of th 

 Luiopean 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 hollow oi 



