THE CLIMATES OF THE OCEAN. 243 
resents the mean or average limits of these constant flows — polar 
and equatorial ; whereas, with almost every wind that blows, and 
at every change of season, the line of meeting between their wa- 
ters is shifted. In the next place, this line of meeting is drawn 
with a free hand on the plate, as if to represent an average ; 
whereas there is reason to believe that this line in nature is vari- 
able and unstable as to position, and as to shape rough and jag- 
ged, and oftentimes deeply articulated. In the sea, the line of 
meeting between waters of different temperatures and density is 
not unlike the sutures of the skull-bone on a grand scale — very 
rough and jagged ; but on the plate it is a line drawn with a free 
hand, for the purpose of showing the general direction and po- 
sition of the channels in the sea, through which its great polar and 
equatorial circulation is carried on. 
525. Now, continuing for a moment our examination of Plate 
IV., we are struck with the fact that most of the thermal lines there 
drawn run from the western side of the Atlantic toward the east- 
ern, in a northeastwardly direction, and that, as they approach the 
shores of this ocean on the east, they again turn down for lower 
latitudes and warmer climates. This feature in them indicates, 
more surely than any direct observations upon the currents can 
do, the presence, along the African shores in the North Atlantic, 
of a large volume of cooler waters. These are the waters which, 
having been first heated up in the caldron (§ 509) of St. Roque, in 
the Caribbean Sea, and Gulf of Mexico, have been made to run 
to the north, charged with heat and electricity to temper and reg- 
ulate climates there. Having performed their offices, they have 
cooled down ; but, obedient still to the " Mighty Voice" which the 
winds and the waves obey, they now return by this channel along 
the African shore to be again replenished with warmth, and to 
keep up the system of beneficent and wholesome circulation de- 
signed for the ocean. 
ft 
