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 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, and covers the ocean with a mantle of warnith 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 warmth 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 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 winter's day would be suflJicient 
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," 
