48 THE PHYSICAL GEOGRAPHY OF THE SEA. 



flared out so as to present a large cooling surface. Here the cir- 

 culation of the atmosphere is arranged by nature ; and it is such 

 that the warmth thus conveyed into this warm-air chamber of 

 mid-ocean is taken up by the genial west winds, and dispensed, in 

 the most benign manner, throughout Great Britain and the west 

 of Europe. 



61. The maximum temperature of the water-heated air-cham- 

 ber of the Observatory is about 90°. The maximum temperature 

 of the Gulf Stream is 86°, or about 9° above the ocean temper- 

 ature due the latitude. Increasing it» latitude 10°, it loses but 

 2° of temperature ; and, after having run three thousand miles 

 toward the north, it still preserves, even in winter, the heat of 

 summer. With this temperature, it crosses the 40th degree of 

 north latitude, and there, overflowing its liquid banks, it spreads 

 itself out for thousands of square leagues over the cold waters 

 around, and covers the ocean with a mantle of warmth that serves 

 so much to mitigate in Europe the rigors of winter. Moving 

 now more slowly, but dispensing its genial influences more freely, 

 it finally meets the British Islands. By these it is divided (Plate 

 IX.), one part going into the polar basin of Spitzbergen, the other 

 entering the Bay of Biscay, but each with a w^armth considerably 

 above the ocean temperature. Such an immense volume of heat- 

 ed water can not fail to carry with it beyond the seas a mild and 

 moist atmosphere. And this it is which so much softens climate 

 there. 



62. We know not, except approximately in one or two places, 

 what the depth or the under temperature of the Gulf Stream 

 may be ; but assuming the temperature and velocity at the depth 

 of two hundred fathoms to be those of the surface, and taking the 

 well-known diff'erence between the capacity of air and of water 

 for specific heat as the argument, a simple calculation will show 

 that the quantity of heat discharged over the Atlantic from the 

 waters of the Gulf Stream in a winter's day would be sufficient 

 to raise the whole column of atmosphere that rests upon France 

 and the British Islands from the freezing point to summer heat. 



Every west wind that blows crosses the stream on its way to 

 Europe, and carries with it a portion of this heat to temper there 

 the northern winds of winter. It is the influence of this stream 

 upon climate that makes Erin the " Emerald Isle of the Sea," 



