THE GULF STEEAM. 397 



traction with an increased localized speed at low declination. That at the 

 time of the contraction there is a deepening of the current at its axis, and 

 that at its expansion it has diminished in depth, but has increased its 

 velocity on the sides. The most marked movement at high declination is 

 an increased speed toward the left side, and but little towards the right 

 side of the Stream. 



The Daily Variation in velocity, also governed by the moon, sometimes 

 amounts to 2^ knots, and is most marked on the surface, being far greater 

 on the West side than on the East side of the Stream. It is greatest at 

 the point of greatest average velocity. This difference in rate has taken 

 place within 3 or 4 hours, as if a large wave travelled up the Stream, its 

 front face being steep, and its rear less inclined. The change has been seen 

 to be accompanied by a tide-rip when the wind was favourable for its 

 formation, and within 6 minutes the speed of the current advanced over 

 half a knot. 



There are, in reality, two periods of increase and two of decrease during 

 the lunar day, the first or highest maximum about 9 hours before the upper 

 transit, and the lesser at 9 hours before the lower transit. Lieutenant 

 Pillsbury thinks the popular belief that the axis of the Stream changes 

 with the wind, is almost wholly due to the Daily Variation. 



At the time of the monthly increase, the minimum current for the day 

 follows the greatest maximum by about 6 hours. In the next 6 hours 

 there is an increase in velocity equal to, or perhaps greater than, the pre- 

 ceding maximum. In the third interval there is a fall in speed, to be 

 succeeded by a still greater maximum 9 hours before the next upper transit. 

 At the time of the monthly decrease in velocity the conditions are reversed, 

 the minimum preceding the maximum, and each succeeding maximum or 

 minimum is less than the preceding. In the interval of change there is a 

 short time of irregular velocities, when the maximum for the day arrives 

 before the lower transit instead of the upper. 



Section 1, hetioeen Cape San Antonio and Yucatan Bank, has been 

 already described in (346), page 370, and the flow of the Equatorial Current 

 from the Atlantic through the Caribbean Sea, on pages 358 — 368. 



Section 2. Across tlie Western entrance of Florida Strait. — This section, 

 125 miles in extent, may be considered the real starting point of the Gulf 

 Stream. Its currents vary greatly in direction, and owing to its great 

 width the velocity is more feeble, and the characteristics which mark the 

 other sections less pronounced. The eddy or counter-current, found on the 

 North side (hereafter described), sometimes reaches this section. 



Section 3. Between Bebecca Shoal and Havana the Straits are about 73 

 miles in width between the 100-fathoms lines. Being near the beginning 

 of the Gulf Stream proper, the current does not fill the strait, but on its 

 Northern side has a neutral zone of varying width, in which, at times, an 

 eddy current sets to the Westward. The observations obtained here show 

 that when the moon is near the Equator, the currents are more Easterly 

 than Westerly, and when near the highest declination they are the reverse, 

 although so weak that for the purposes of navigation they are not of much 

 value. 



Between Eebecca Shoal and Cuba the Currents have been long known 



