372 OBSERVATIONS ON THE CURRENTS. 



keep up a well-defined movement of its water. Probably, in or about lat. 

 27"^ N., long. 90° W., a considerable portion of the Current which passed 

 through the Yucatan Channel finds its way into the Gulf Stream. Here- 

 abouts it would appear that the Currents are intricate, and difficult to 

 ascertain by a day's run, from their conflicting influence upon the ship's 



course. 



(351.) In the Supplement No. 2, 1891, to the Saihng Directions for the 

 Caribbean Sea and Gulf of Mexico, published by the United States Hydro- 

 graphic Office, it states, the Current coming up through the Yucatan 

 Channel, takes a general North- Westerly direction, and then runs North- 

 ward to about the latitude of the Rio Grande. Thence it flows Easterly 

 until ofl' the Delta of the Mississippi, where it is diverted to the S.E., and 

 continues on to the Straits of Florida. Off the mouth of the Rio Grande, 

 and thence to Vera Cruz, anywhere within 100 miles from the land, a 

 Southerly counter-current is usually found. When off the mouths of the 

 Mississippi, within about 50 miles from the shore, a Westerly current is 

 almost invariably encountered. This Current varies from 1 to 2 knots per 

 hour, growing stronger as the land is neared, and must be allowed for by 

 vessels approaching the passes. A strong, or long-continued Westerly 

 wind, however, occasionally has the effect of neutralizing this current, and 

 sometimes, though rarely, reverses it. A strong and long-continued 

 Norther may have the effect of producing a general Southerly set all over 

 the Gulf. In the centre of the Gulf there is seldom any current except in 

 the case of a heavy Norther. 



(352.) The following refers to the Currents on Tortugas Bank. Captain 

 H. Miles, ship Illustrious, states : — " April 16th, 1859, at noon, in lat. 

 25° 36' N., long. 83° 33' W.; at 8 p.m. sounded in 38, 35, 33, and 32 

 fathoms, bottom at first depth coarse white sand, with broken shells, and 

 gradually becoming of a greenish hue as the water shoaled. The wind 

 being shy from S.W., I anxiously anticipated the Current which Blunt 

 assures us 'runs hvely to the Southward along the edge of Tortugas 

 soundings,' in lieu of which, by a series of first-class observations, verified 

 on making Bush Kay Light, I ascertained the set N.N.E., 1-^ mile per 

 hour, since striking soundings. In fact, coupled with former experience, 

 I am convinced that, although during the influence of Northerly and 

 Easterly winds, a S.E. Current of considerable strength most certainly 

 exists, yet with a Southerly breeze it is not only neutraHzed, but, as in 

 the present instance, may set in a contrary direction, or to N.E." 



(353.) The mean temperature of the water of the Gulf of Mexico is pro- 

 bably as high as any part of the Ocean, from several manifest causes, and 

 hence it is, on the shores of this sea, that some of those nurseries of the 

 Sargasso weed exist (292), which, torn from its habitat by the force of the 

 current, &c., is drifted into that great central area of the Atlantic, to 

 which it gives the characteristic pecuharity. 



It is also probable that animal life is peculiar and abundant in these 

 iepid waters. '' Lieutenant Evans remarks : — " The phosphorescent hghts 

 i)bserved in the Mexican Sea shine with greater briUiancy (April) than I 

 had noticed elsewhere ; some of these were very large, and flashed like 

 the nriming of a gun, sometimes at a long distance from the ship. I 



