50 THE PHYSICAL GEOGRAPHY OF THE SEA. 



Britain and tlie west of Europe. The mean temperature of tlie 

 water-heated air-chamber of the Observatory is about 90°-. The 

 maximum temperature of the Gulf Stream is 86°, or about 9° 

 above the ocean temperature due the latitude. Increasing its 

 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, covering 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 in- 

 fluences 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 warmth considerably above the ocean temperature. Such an im- 

 mense volume of heated 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. 



152. We know not, except approximately in a few places, 

 Depth and temper- what the dcpth 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 difference 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 win- 

 ter's day would be sufficient to raise the whole column of atmos- 

 phere that rests upon France and the British Islands from the 

 freezing point to summer heat. 



153. Every west wind that blows crosses the stream on its way 

 Contrasts of cii- to EuroDC, and carries with it a portion of this heat 



mates in the same -'■' 'in- t 



latitudes. to tcmpcr thcrc the northern wmds oi winter. It 



is the influence of this stream upon climate that makes Erin the 

 ^' Emerald Isle of the Sea," and that clothes the shores of Al- 

 bion in evergreen robes ; while in the same latitude, on this side, 

 the coasts of Labrador are fast bound in fetters of ice. In a val- 

 uable paper on currents,* Mr. Eedfield states, that in 1831 the 



* American Journal of Science, vol. xiv., p. 293. 



