256 THREE CRUISES OF THE “ BLAKE.” 
flows through the Windward Passage, represents a far greater 
mass than that which can find its way into the Gulf of Mexico 
through the Straits of Yucatan, or that of the stream flowing 
north through the Straits of Bemini. "This is the actual Gulf 
Stream, a body of superheated water filling the whole straits ; it 
has an average depth of about three hundred and fifty fathoms, 
and a velocity extending to the bottom of at least three and a 
half miles an hour.' 
The section of the Yucatan Channel is too small to allow for 
an outflow equal to the inflow into the Caribbean,” so that, after 
the trades have ceased to force the equatorial water into the Car- 
ibbean basins, it must remain there a considerable length of 
time before it passes into the Gulf of Mexico, where, owing 
to similar differences between the rate of inflow and outflow, 
the water must become still more superheated. 
We must therefore consider the Gulf Stream proper, as it 
emerges from the Straits of Bemini, as an immense body of su- 
perheated water, retaining an initial velocity which originated in 
lower latitudes; then losing both its velocity and its heat on tts 
way north? (See Fig. 176.) 
The Straits of Florida have a width of about forty-eight miles 
between Jupiter Inlet and Memory Rock; the greatest depth is 
439 fathoms, and the cross-section 430,000,000 square feet. At 
three knots the delivery would be, as calculated by Commander 
Bartlett, about 436,000,000,000,000 tons a day,— an amount 
of warm water far less than that we find over the North Atlantic, 
' Current observations taken by Mit- the section of the Gulf Stream observed 
chell off the coast of Cuba, in the deep by the “Challenger” was cooled 1° C., 
part of the Gulf Stream, show that it has as compared with that of the Bermudas 
a nearly uniform and constant velocity to New York. The Gulf Stream retains 
for a depth of 600 fathoms, although the its heat as a surface current as long as the 
temperature varies 40° F, temperature is sufficiently high to make 
? А part of this water emerges again it lighter than the surrounding water. 
at a higher temperature between Guade- Its greater salinity at last causes it to 
loupe and Hayti, and joins that portion sink below the comparatively fresher wa- 
of the equatorial current which finds its ter of northern latitudes. Similarly, the 
way into the Windward Passage. This arctic current, when it reaches a cer- 
increased temperature may be due to its tain latitude along our eastern coast, sinks 
passing over shoals aud banks at the from its greater specific gravity below the 
northeastern end of the eastern basin of warmer surface currents, and continues 
the Caribbean. its way south as an undercurrent of cold 
3 Between Halifax and the Bermudas water. 
