370 OBSERVATIONS ON THE CURRENTS. 



(346.) The Currents in this channel were carefully observed by the 

 oflBcers of the United States Coast Survey steamer Blake, in March and 

 April, 1887. We here give the results of these investigations, as detailed 

 by Lieutenant J. E. Pillsbury, U.S.N. 



It was found that the Northerly current did not fill the whole channel, 

 and the surface currents on either side were variable in their direction. 

 On the Eastern side of the channel, within 20 miles of Cape San Antonio, 

 there was a light but persistent flow into the Caribbean Sea, its direction 

 varying according to the declination of the moon. At the time of low 

 declination its direction was between N.E. by N. and E.S.E., the mean 

 being N.E. by E.; at high declination it was between East and S.E. by S., 

 the mean E.S.E. The average velocity at 3^ fathoms was only from 

 0-50 to 0*75 knot per hour. At high declination an eddy current was 

 found setting from ofif Cape Antonio along the Colorado Reefs, but at 30 

 miles off shore it set to the Northward and Eastward. 



On the Western side of the channel, in 23 fathoms, 5 miles inside the 

 100-fathoms line of Yucatan Bank, the interference of the stream current 

 with the tidal current was very noticeable ; the flood tide running about 

 N.W. for 18 hours, and on the ebb it ran to the Eastward. 



In mid-channel the current varied but little from North, the average 

 being N.E. by E. The axis, or part of greatest velocity, was found to be 

 West of mid-channel, with a bodily movement to right and left, according 

 to the moon's declination. The velocity averaged about 2 knots, the 

 maximum (about 3 knots) being experienced 10 hours before the moon's 

 transit. 



The Blake was anchored at various distances between Cape San Antonio 

 and Contoy Island, when the mean surface velocity of the Northerly 

 current was as follows : — At 25 miles East of Contoy, 3-65 knots an hour ; 

 at 30 miles, 3-25 knots ; at 35 miles, 2-37 knots ; at 45 miles, 2-79 knots ; 

 at 60 miles, 1-56 knot ; at 76 miles, 1*07 knot; and at 90 miles 0-51 knot. 



At the first position, which is 5 miles off the 100-fathoms line of 

 Yucatan Bank, an extreme daily variation in speed of 3'95 knots was 

 found at high declination of the moon. It is stated in the " Annales 

 Hydrographiques," 1889, page 236, that on one occasion it here attained 

 a velocity of 6^ knots an hour, 



(347.) Gulf of Mexico. — The Mexican Sea appears to be the receptacle 

 and terminus of all the waters flowing Westward. It was formerly con- 

 sidered that the Current through the Yucatan Channel diverging East- 

 ward and Westward, the Western branch circulated around the whole of 

 the GuH to Westward and Northward, and thence flowing Eastward and 

 South-Eastward, at rates varying from 14 to 31 miles per day, that it 

 formed what was known as the " Great Whirlpool "* of the Mexican Gulf, 

 and then joined the Eastern, and perhaps principal, branch of the Yucatan 

 Current, forming the mighty Gulf Stream. Later investigations have 

 shown that the general circulation of the water of the Gulf of Mexico is 

 erratic in direction and feeble in force. Observations at twelve anchorages 



• Sw Dr. Lorimar, April 21, 1769, "Transactions of the Amerioan Philosophical 

 Society, Philadelphia." vol. i., p. 250. 



