196 THE GULF STREAM. 
Perhaps the best example of the unstable equilibrium existing be-— 
tween adjoining oceanic areas is furnished by the heaping up of the 
waters driven by the tradewinds into the Gulf of Mexico from the 
Caribbean. The amount of this accumulation has actually been meas- 
ured by officers of the United States Coast Survey. It gives an addi- 
tional force at work to keep up the efficiency of the Gulf Stream. The 
Gult of Mexico is considered by Mr. Hilgard as an immense hydro- 
static reservoir, rising to the height of more than 3 feet* above the 
general oceanic level, and from this supply comes the Gulf Stream, 
which passes out through the Straits of Bemini, the only opening left 
for its exit. 
Arago, Lenz, and Leonardo da Vinci before them, maintained that, 
since the water of the equator was greatly heated and lighter and 
attained » higher level, there was a flow of the surface waters towards 
the poles, a compensation being established by the flow of lower strata 
from the poles to the equator. The principal features of this thermic 
theory have of late found their most efficient exponent in Dr. Carpen- 
ter. The results of his experiments to prove this theory upon a small 
scale seemed to show that the cooling of the waters at the pole and 
their rapid fall were a more efficient force than the heating of the 
water at the equator. Ferrell has called attention to the phenomenon 
that cold water at the bottom will be swung more to the westward than 
the water at the top, which will be turned in an easterly direction. As 
the particles of water ascend, they retain the velocity they had in 
deeper parts of the ocean, and thus, when reaching either the surface 
or lesser depths than their original position, they must show themselves 
as producing a westerly current. This current, deflected by the con- 
tinental masses as it strikes the east coast, would then be set in motion 
towards either the north or south pole. At the equator, the water 
which flows westward from the eastern shores of the continental masses 
can only be replaced by the compensating waters flowing to it from the 
north and south. This circulation fairly agrees with the phenomena 
observed in the South and North Atlantic. 
It is interesting to trace the gradual development of our knowledge 
of the Gulf Stream and to see how far-reaching has been the influence 
of the oceanic currents upon the explorations of maritime nations, and 
the effect these have had in their turn on the discovery of America 
and its settlement.t The hardy Norse navigators, nearly five hundred 
years before Columbus, sailed along the eastern shores of Greenland 
and America, and extended their voyage possibly as far south as Nar- 
ragansett Bay, following the Labrador current, which swept them along 
our eastern shores. It was well known to navigators that upon the 
—_—— - —-. — es: é. we a 
* By a most careful series of levels, run from Sandy Hook and the mouth of the 
Mississippi River to St. Louis, it was discovered that the Atlantic Ocean at the first 
point is 40 inches lower than the Gulf of Mexico at the mouth of the Mississippi. 
+See Kohl, J. G., Geschichte des Golfstroms und seiner Erforschuna, 1868. 
