TEMPERATURE AND MOVEMENTS OF THE DEEP SEA. 129 
away the water, of course water must come in to fill up its 
place from some other part of the pond. That is a horizontal 
circulation ; and the horizontal circulation in the Atlantic is 
produced in this way. The Trade Winds are always blowing 
between the tropics from east to west ; they move along an 
enormous mass of water, excessively heated by the action of the 
sun, constituting the Equatorial Current, and drive it into the 
G-ulf of Mexico ; it circulates there, and comes out from the 
Florida channel as a rapid current. But that rapid current, 
there is strong reason to believe, is not as deep as is commonly 
supposed ; and the amount of the heat it carries has been very 
much over-estimated. As it passes along the coast of the 
United States (separated from it by a current of cold water that 
comes down from the north), it spreads itself out, becoming pro- 
portionally thinner, and at the same time slackening in its rate 
of movement. Its temperature progressively falls, especially 
in winter ; and when the stream is reduced to a mere surface- 
film, it cannot retain a temperature much above that of the 
atmosphere. About half of it, when it come to the Azores, 
or Western Islands, turns round again, goes near the African 
coast, and returns into the Equatorial current; completing 
therefore one portion of the circulation I have spoken of. The 
other half goes on past the Banks of Newfoundland ; there it 
meets the surface of the Arctic stream, which breaks it up 
or 64 inter-digitates ” with it — this word expressing an action 
like that of passing one set of fingers through another. I admit 
that a portion of the Gulf Stream goes north, but the greater 
part of it is stopped and cooled by this Polar current coming 
down ; and it is the southward continuation of this cold surface- 
current from the coasts of Greenland and Labrador, which gives 
the low winter temperaturh to the seaboard of the United States, 
and which forms the complement of the northern half of the 
Gulf Stream. It is known that Polar water also underlies the 
Gulf Stream ; for if you send the thermometer sufficiently deep, 
you find a very low temperature beneath this extraordinary 
surface-current, even in the Florida channel. 
I have adverted to the Gulf Stream, because I want to show 
the important influence of the upper movement of warm water 
of which I previously spoke, which is quite independent of the 
Gulf Stream. Suppose that the narrow peninsula of Mexico, or 
the narrowest part of it, the Isthmus of Panama, which connects 
North and South America, were broken through — as it will 
be in course of ages by the action of the sea — so that a free 
course should be given to the Equatorial current ; it would 
then go right through into the Pacific Ocean, and we should 
have no Gulf Stream at all. But even in that case, I think 
our climate would not suffer so much as most persons believe ; 
VOL. XI. — NO. XLIII. K 
