142 Miscellaneous. 



duces the following generalizations in regard to the interchange of 

 birds between America and Europe. 



European birds, especially the land species, reach Greenland and 

 return to the continent by way of Iceland, the Faroe Islands forming 

 a stepping-stone from Great Britain and Scandinavia. In very rare 

 instances species seem to proceed direct to Greenland, without stop- 

 ping in Iceland, although this may be due to the fact that while 

 visiting Iceland they have not yet been noted there by any naturalist. 



The European birds found on the continent of North America 

 reach it by autumnal movement from Greenland in company with 

 strictly North American species. 



Birds of North America rarely, if ever, reach England from 

 Greenland by direct spontaneous migration by way of Iceland, as 

 shown by the fact that only three of the American birds occurring 

 in Greenland are found in Iceland, and that few of the American 

 species observed in Europe are found in Greenland at all. 



Most specimens of American birds recorded as found in Europe 

 were taken in England (about fifty out of sixty-nine), some of them 

 in Heligoland ; very few on the continent (land birds in only five 

 instances). 



In nearly all cases these specimens belonged to species abundant 

 during summer in New England and the eastern provinces of British 

 America. 



In a great majority of cases the occurrence of American birds in 

 England, Heligoland, and the Bermudas has been in the autumnal 

 months. 



The clue to these peculiarities attending the interchange of species 

 of the two continents will be found in the study of the laws of the 

 winds of the northern hemisphere, as developed by Prof. Henry and 

 Prof. Coffin. These gentlemen have shown (see Prof. Henry's 

 articles on Meteorology, ' Report of Commissioner of Patents for 

 1856,' p. 489) that the "resultant motion of the surface atmosphere, 

 between latitudes 32° and 58'^ in North America, is from the west, 

 the belt being twenty degrees wide, and its greatest intensity 

 in the latitude of 45°. This, however, must oscillate north and 

 south, at different seasons of the year, with the varying declination 

 of the sun. South of this belt, in Georgia, Louisiana. &c., the 

 country is influenced, at certain seasons of the year, by the north- 

 east trade-winds, and north of the same belt by the polar winds, 

 which, on account of the rotation of the earth, tend to take a direc- 

 tion towards the west. It must be recollected that the westerly 

 direction of the belt here spoken of is principally the resultant of 

 the south-westerly and north-westerly winds alternately predomi- 

 nating during the year." 



From these considerations and facts, therefore, we are entitled to 

 conclude that the transfer of American birds to Europe is principally, 

 if not entirely, by the agency of the winds, in seizing them during 

 the period of their migration (the autumnal especially), when they 

 follow the coast or cross its curves, often at a considerable distance 

 from land, or a great height above it. Carried off, away out to sea. 



