THE GULF STREAM. 249 
ered by Mr. Hilgard as an immense hydrostatic reservoir, rising 
to the height of more than three 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 a higher level, there was a flow of the sur- 
face 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. Carpenter. 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 west- 
ward than the water at the top, which will be turned in an east- 
erly 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 continental 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 continen- 
tal 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 explora- 
tions of maritime nations, and the effect these have had in their 
1 By a most careful series of levels, first point is forty inches lower than the 
run from Sandy Hook and the mouth of Gulf of Mexico at the mouth of the Mis- 
the Mississippi River to St. Louis, it was sissippi. 
discovered that the Atlantic Ocean at the 
