224 LIGHT SCIENCE FOR LEISURE HOURS. 



of Buchan, the meteorologist, that the north-easterly 

 current above (referred to produces an afflux of warmth 

 brought to the British Isles by the water that laves our 

 western coasts.' He proceeds : ' There is ample evidence 

 that the cold of some parts of the north polar area is 

 greatly mitigated by an afflux of water bringing with 

 it the comparative warmth of temperate seas. It has 

 long been known that cocoa-nuts, tropical seeds, trunks 

 of tropical trees, timbers and spars of ships wrecked far 

 to the south, and sometimes portions of their cargo, 

 are found on the shores of the Western Hebrides, the 

 Orkney, Shetland, and Faroe Islands, the north of 

 Norway, and even Spitzbergen ; and since their trans- 

 sport has taken place just in the course of the Gulf 

 Stream if prolonged to the north-east, their arrival has 

 been accepted almost without question as evidence of 

 its agency. The evidence furnished by the surface tem- 

 perature of that north-eastern portion of the Atlantic 

 Ocean which intervenes between Iceland and the North 

 Cape, and then stretches away to the eastward between 

 Spitzbergen and Nova Zembla, seems at first sight con- 

 clusive to the like effect. A large amount of additional 

 thermometric evidence has been collected of late years; 

 and this has been most ably digested by the eminent 

 German geographer, Dr. Petermann, who has recently 

 put forward a series of maps for different periods of the 

 year, in which these observations are embodied, and 

 their results made obvious to the eye by the course of 

 the * lines of equal temperature,' which in the summer 

 pass between Iceland and the Shetland Islands, a little 



