25G 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 Sti'aits of Yucatan, or that of the stream flowing 

 north throuo'h 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 Gidf Stream proper, as it 

 emerges from the Straits of Bemini, as an immense body of su- 

 perheated w^ater, retaining an initial velocity w^hich originated in 

 lower latitudes ; then losing both its velocity and its heat on its 

 way north.^ (See Fig. 176.) 



The Straits of Florida have a width of about forty-eight mfles 

 between Jujjiter 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 w^ater 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 



- A 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- 



inereased temperature may be due to its tain latitude along our eastern coast, sinks 



passing over shoals and 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. 



