THE GULF STREAM. 193 
The more systematic work of the officers of the Coast Survey first 
proved the existence of vast bodies of water, of considerable thickness, 
and of very different temperatures at corresponding depths, moving in 
opposite directions. It is to the Coast Survey that we owe the demon- 
stration of the fact that the waters of the polar regions pour into the 
tropics along the bottom, just as the warmer equatorial waters flow 
across the temperate zones near the surface, and make their influence 
felt in the polar regions. 
The submarine ridges interrupt the flow of these cold polar waters, 
and form the so-called closed basins, with a higher bottom temperature 
than that of the adjoining oceanic basin. The effect of such ridges 
upon the bottom temperature was first traced by the soundings of the 
Porcupine in the North Atlantic and in the Mediterranean. Subse- 
quently the Challenger discovered several such ineclosed seas while 
sounding in the East Indian Archipelago. 
The correctness of these results has been confirmed by the Coast 
Survey, from soundings in the Caribbean and in the Gulf of Mexico; 
their bottom temperature (at a depth of over 2,000 fathoms) is exactly 
that (393°) of the deepest part of the ridge, at about 800 fathoms, which 
separates them from the oceanic Atlantic basin, With its temperature 
of 56° at the depth of 2,000 fathoms. 4 
The presence of thick layers of water having a higher bottom tem- 
perature than that of adjoining areas would indicate the presence of 
ridges isolating these warmer areas from the general deep-sea oceanic 
circulation. A map of the Atlantic, made entirely with reference to 
the temperatures, would correspond to a remarkable degree with the 
topography of the bed of the ocean, and show how and where the breaks 
in the continuity of the circulation, both for the arctic and antaretie 
regions, occur in the Atlantic. 
It was not however until the Miller-Casella thermometer came into 
general use for deep-sea investigations that a degree of accuracy before 
unattainable in oceanic temperature became possible. It soon was a 
well-recognized fact that as we go deeper the temperature diminishes, 
and that at great depths the temperature of the ocean is nearly that 
of freezing. In 1868~69, in the Faroes Channel, the Porcupine found 
-a temperature of —1.4° C. at a depth of 640 fathoms, and a tempera- 
ture of 0° C. at 500 fathoms, this being a southern extension, as was 
subsequently found, of the deep basin of 1,800 fathoms lying between 
Norway and Iceland. The same temperature, 0.9° C., occurs under 
the equator at a depth of about 2,300 fathoms, while 5° C. is found at 
a depth of 300 fathoms. As early as 1859 the Coast Survey had re- 
corded in the Straits of Florida a temperature of 40° F. (4.4° C.) at a 
depth of 500 fathoms, while at the surface the temperature was 80° F, 
(26.79 C.). Beyond 1,000 fathoms the temperature diminishes very 
slowly. The Challenger also found a temperature somewhat below zero 
off the Rio de la Plata, at a depth of about 2,900 fathoms. 
H. Mis. 334, pt. 1-13 
