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POPULAR SCIENCE REVIEW. 
because though we should lose some portion of our warm 
south-westerly winds, this constant flow of warm water which is 
taking place in the whole mass of the North Atlantic — from the 
southerly area directly towards the north and north-east, so 
as to enter the Polar area — will still continue, carrying with it 
a temperature which, taken altogether, is very much greater 
than that of the Grulf Stream. For the last we know definitely 
of the Grulf Stream shows that it is thinned off to a layer of 
certainly not more than 50 fathoms, and perhaps less, and 
reduced to a temperature of about 65 degrees ; whereas this 
great slowly-moving mass of water carries a temperature higher 
than the temperature of the latitude down to 500 or 600 
fathoms’ depth ; and as the surface is cooled, warm water from 
below will come up to take its place ; and in this manner will 
carry into the Polar area a great body of heat derived from the 
general surface of the Temperate and Tropical oceans. And this 
I believe has taken place in all Geological periods, quite irre- 
spective of any such local accidents as those which produce the 
(Gulf Stream. There must have been in all Geological periods 
a movement of this warmer water from the Equatorial towards 
the Polar area, and conversely (and this is most important 
geologically) a movement of cold water in the depths of the 
oceanic basins, from the Polar towards the Equatorial area, 
bringing with it the' characteristic animals of the Polar 
climate. 
But you will ask, and very properly, “ What evidence have 
you of this movement ? ” and ££ What produces this move- 
ment?” Now, the evidence of such a movement lies in the 
fact that cold water could not remain cold water at the bottom 
of these Oceanic basins, if the supply were not kej)t up from the 
cold basins at the Poles. I will give you an illustration. We 
were at work this last summer in the Mediterranean ; and we 
found its condition most curiously different in regard to tem- 
perature from the condition of the Atlantic. The Mediterranean 
is a basin which, to use a Scotch word, is ££ self-contained it 
is shut in almost entirely, the Strait of Gibraltar being its only 
communication with the outside ; and that Strait is so shallow 
at its outlet, that no communication between the deep water of 
the Mediterranean and that of the Atlantic can possibly take 
place. The Mediterranean goes down in some parts to a depth 
of 2,000 fathoms ; we ourselves sounded to above 1,700, that is 
from about 1 1,000 to 12,000 feet. We found the surface very hot, 
being there in August and September ; the temperature of the 
surface of the sea rose to 78 degrees in some instances. But 
we found that hot temperature limited to a very shallow layer 
indeed; we lost 10 or 15 degrees of that heat in 30 fathoms; 
at a depth of 30 fathoms we found the temperature perhaps 63, 
