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POPULAR SCIENCE REVIEW. 
as London. Nairn, on the desolate and frozen coast of 
Labrador, is in the same latitude as Dublin ; yet the former has 
only a mean temperature of 28°, whilst Dublin has a mean 
temperature of 49°, or nearly double the warmth of Nairn. 
The cause of this great disparity in the relative temperature 
of places lying in the same parallels of latitude is to be found 
in the prevalence of certain winds and oceanic currents, which 
cause the isothermal line to bend northwards so many degrees 
in passing from west to east. 
The ocean-current in which we are especially interested is 
that mighty stream which issues from the Gulf of Mexico, 
flows in a north-easterly course across the Atlantic, and is com- 
monly known as the “ Gulf-Stream.” 
Since 1842, when the energetic Captain Maury, of the United 
States Navy, first drew the attention of the American Govern- 
ment to the importance of preparing 66 wind and current 
charts,” the Gulf-Stream has not wanted observers and his- 
torians. This remarkable oceanic current is about 25 miles in 
breadth off Cape Florida, and it increases to 127 miles off 
Sandy Hook, whilst its depth diminishes from 1,000 to 200 ft. 
and under as it proceeds northwards. From the American 
Coast and from the banks of Newfoundland it is deflected 
across the Atlantic, reaching the Azores in about 78 days, after 
flowing nearly 3,000 miles. Our own islands enjoy a portion of 
its warmth; and even Spitzbergen, in latitude 79° north, feels 
its influence, and before its warm breath the glaciers are stopped 
abruptly in their descent to the sea. 
Mr. Croll has estimated the total quantity of water conveyed 
by the Gulf-Stream to be equal to that of a current of water 
50 miles broad and 1 ,000 ft. in depth, flowing at the rate of 
4 miles an hour, with a mean temperature of 65°. Before its 
return from its northern journey, he concludes it has cooled 
down at least 25°. Each cubic foot of water, therefore, has 
carried from the tropics upwards of 1,500 units of heat, or 
1,158,000 foot-pounds.* Principal J. D. Forbes has calculated 
that the quantity of heat thrown into the Atlantic Ocean by 
the Gulf-Stream on a winter’s day would be sufficient to raise- 
the temperature of the air which rests on France and Great 
Britain from the freezing point to summer heat. 
At the very time the Gulf-Stream is rushing in greatest 
volume through the Straits of Florida, and hastening to the 
north, a cold counter-current is descending from Baffin’s Bay 
* According to the above estimate of the size and velocity of the stream, 
5,575,680,000,000 cubic feet of water are conveyed every hour by the Gulf- 
Stream, or 133,816,320,000,000 cubic feet per day. The calculations of 
Sir John Herschel and Captain Maury make the amount still greater. 
