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winter winds are northeasterly and the summer winds southeasterly; as a consequence, during the winter season, the west-going branch or portion of the inflowing waters is driven southward upon Campeche Bank, and the northward flow, usually found in the deeper waters lying between Campeche Bank and the Mississippi Passes, practically disappears.

During most seasons of the year there is a fairly definite current setting from Yucatan Channel toward the Mississippi Passes and extending over about one-half of this distance; also a southeasterly current extending from near the Passes to the western end of Florida Strait.

The currents in the western end of the Gulf, from Vera Cruz to Galveston, are weak and uncertain. The currents in the deeper portions of the Gulf are due largely to prevailing winds.

Counter currents occur along the northern and western coasts of Cuba, in the Bay of Campeche, along the coast west of the Mississippi Passes, and probably off nearly the entire Gulf coast of Florida. The current along the Florida Keys is variable and uncertain.

The Gulf Stream is described separately under that heading. Mariners traversing the area through or adjacent to which the Gulf Stream passes should familiarize themselves as thoroughly as possible with this extraordinary ocean current.

STRAITS OF FLORIDA-CAUTION AS TO CURRENTS

The attention of navigators is called to the fact that most of the wrecks on Florida Reefs occur in the case of vessels bound southward, especially at night; they generally occur on reefs lying about halfway between the lights; and the region of maximum frequency of wrecks is between Carysfort Reef and Alligator Reef, and to a less extent between Fowey Rocks and Carysfort Reef and between Alligator Reef and Sombrero Key.

From a consideration of the data it can be stated that nearly all casualties are due to one cause-an underestimate of the strength of the Gulf Stream against the vessel. This leads to two errors in navigation: First, the distance made good over the bottom is less than assumed or indicated by the log, and when skirting the reefs the course is changed too soon for the next light and before sighting it; second, the vessel underrunning her log is closer to the reefs than indicated by the four-point bearing, and this error is greater for slow vessels than for fast ones.

At night, when bound southward and navigating at a safe distance from the reefs between Fowey Rocks and Sombrero Key, it is on the side of safety to assume that the vessel is steaming against a 3- or 4knot current, and from one light to hold a course that will insure clearing the reefs until the next light is sighted. It is also well to remember that near the reefs there is a tidal current, possibly as much as 0.5 knot in places directly on and off the reefs on the rising and falling tides, respectively.

On the other hand, when bound northward and following Florida Reefs between Sombrero Key and Fowey Rocks it is on the side of safety to underestimate the velocity of the Gulf Stream with the vessel; the courses should be laid well clear of the reefs, which is

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the usual practice. Vessels are rarely lost on Florida Reefs when bound northward, except when crossing the Stream from Habana and making the reefs in misty or rainy weather.

The following are extracts from a report of a stranding:

Rounded Great Isaac Light at a distance of 24 miles, steered by compass and log 227° true for 20 miles, and then steered 224° true. By bow and beam bearing Fowey Rocks Light was 12 miles distant when abeam, but on account of the northerly current it was probably about 7 miles. The vessel stranded on the north end of Long Reef, having had a northerly set of 17 miles, or an average of about 24 knots for the crossing from Great Isaac Light to Florida Reefs.

Along the keys there is a slight tidal drift, of not more than 0.5 knot, setting on and off the reefs. This current will probably not be noticeable at a greater distance from the reefs than 1 mile. Between the keys, in the passes connecting Hawk Channel and Florida Bay, the current has considerable velocity (3 to 4 knots) in the immediate vicinity of the openings, and is felt to some extent, probably, on and beyond the usual sailing line in Hawk Channel. When not influenced by winds the maximum current northwestward into Florida Bay and southeastward into Hawk Channel through the openings between the keys occurs about 1 hour before high and low waters, respectively, in the straits. The northwesterly current is increased by easterly winds and the southeasterly current by westerly winds, due to the effect of these winds in driving out or piling up, respectively, the water in Florida Bay.

CURRENTS, STRAITS OF FLORIDA TO CAPE HATTERAS

On the eastern side of the Gulf of Mexico for a distance of possibly 100 miles outside the 100-fathom curve, southeasterly currents prevail and velocities as high as 2.5 knots have been reported. The Gulf Stream investigations indicated that the strongest current into the Straits of Florida is found near the 1,000-fathom curve westward of Dry Tortugas, and that velocities of 1.5 to 2 knots are frequent in that locality. Approaching Dry Tortugas from the Gulf should therefore be regarded as a difficult run, as a vessel will overrun her log, and observations are the principal guide; currents may be expected at all times, but variations occur both in direction and velocity, due to the season of the year and the winds. Approaching the passage westward of Rebecca Shoal from northward, a number of vessels have stranded on New Ground Shoal.

From Florida Straits to Cape Hatteras, vessels follow the Gulf Stream, passing about 12 miles southwestward of Dry Tortugas Lighthouse, about 14 miles southward of Rebecca Shoal Lighthouse, then following Florida Reefs about 8 miles off, and passing Fowey Rocks at a distance of 10 to 12 miles and Jupiter Inlet Lighthouse 15 miles. The velocity of the current varies greatly in different localities, and is also subject to sudden changes, due to wind, differences in barometric pressure, and the like, so that no fixed hourly rate can be given. Frequently, high velocities will be carried between certain points and suddenly dropping off between others. The position should therefore be checked whenever possible by bearings. The ship speed plus supposed rate of current should not be assumed to

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fix the position. The greatest velocity will be found between Carysfort Reef and Jupiter Inlet, ranging from 2 to 41⁄2 knots.

From 15 miles off Jupiter Inlet Lighthouse make good the course 1°30' true (N. 1 E. mag.) for 208 miles to latitude 30°25′ N., longitude 79°40′ W. This should lead from 12 to 18 miles outside the 100-fathom curve, and should give a current nearly equal to the average made between Fowey Rocks and Jupiter.

When approaching Diamond Shoal great care must be taken to have a correct location for the vessel. The currents are subject to wide variations, as indicated by the observations on the light vessels. At times during both summer and winter the Gulf Stream has great velocity; at other times none will be found, or a southerly set may be experienced with northerly winds. The general direction of the stream is northeast with a velocity of 1 to 2 knots, but on nearing Diamond Shoal Lightship the current is said to set well to the eastnortheast and at other times nearly north. Overallowance and this northerly set have been fatal to many vessels. If a northerly gale is encountered between Jupiter and Cape Hatteras, some navigators keep closer inshore to get on soundings before reaching Diamond Shoal.

THE GULF STREAM

The Gulf Stream sets eastward and northward through the Straits of Florida, and after passing between Fowey Rocks and Little Bahama Bank it continues northward and then northeastward, following the general direction of the 100-fathom (183 m) curve as far as Cape Hatteras.

In general, the Gulf Stream as it issues into the sea through the Straits of Florida may be characterized as a swift current of highly saline blue water whose upper stratum is composed of warm water. At its junction with ordinary sea water, the edges may frequently be recognized in moderate weather by the ripples which occur as well as by the difference in color. Northward, in the cooler regions, the evaporation from its surface, when the temperature of the air is lower than that of the water, is apparent to the eye. In addition, in the lower latitudes, the stream carries with it a quantity of weed known as gulf weed, which is familiar to all who have navigated its waters.

The axis of the Gulf Stream, or line of greatest velocity, lies from 10 to 20 miles eastward of the 100-fathom (183 m) curve.

Between Cuba and the Florida Reefs, off Habana, the axis of the stream is nearer the Cuban coast; but after making the bend between Salt Key Bank and Florida Reefs, the axis of the stream approaches the coast of Florida and lies from 4 to 11 miles outside the 100-fathom (183 m) curve.

The mean surface velocity of the Gulf Stream is 3.5 knots at a point 111⁄2 miles east of Fowey Rocks and 2.2 knots at a point 60 miles south of Rebecca Shoal. These points are on the axis of the stream, or where the current is a maximum, the velocity of the stream decreasing gradually from these central points as the edges of the stream are approached. These velocities are affected considerably by prevailing winds.

The following tables give the mean surface velocity of the Gulf Stream in two cross sections in the Straits of Florida.

On issuing into the sea northward of Little Bahama Bank the Gulf Stream loses the relatively great velocity which characterized it within the Straits. There is a gradual decrease to a velocity of about 2 knots off St. Augustine, Fla., in latitude 30° N. Here the Gulf Stream is joined by the Antilles Current, which flows northwesterly along the open ocean side of the West Indies before uniting with the Gulf Stream.

The Antilles Current, like the Gulf Stream, carries warm, highly saline water of clear indigo blue. The union of the two currents gives rise to a broad current possessing about the same characteristics as the Gulf Stream within the Straits except that the velocity is much reduced. The combined current turns more and more easterly so that off the coast of Georgia, the Gulf Stream bears northeast, maintaining this general direction past Cape Hatteras.

From within the Straits the axis of the Gulf Stream runs approximately parallel with the 100-fathom (183 m) curve as far as Cape Hatteras, a distance of about 800 geographical miles, but at varying distances from the shore, which sweeps northward in a sharper curve than does the 100-fathom (183 m) curve. Within the Straits it is about 10 miles offshore; in the bight off the coast of Georgia the distance is about 100 miles; and at Cape Hatteras it is about 35 miles.

Earlier systematic observations on the Gulf Stream dealt with the temperature of the water rather than its motion and the axis taken to be along the line of highest temperature obtained. Later the axis was taken to mark the line of greatest velocity. Ordinarily it is assumed that the two axes coincide, but this is by no means certain. The thermometer, although it indicates the limits of the stream in a general way, is therefore only an approximate guide to the velocity of the current, nor is it to be assumed that the northerly set will be lost when the thermometer shows a region of cold sea water.

Within the Straits the lateral boundaries of the Gulf Stream can be fixed with considerable precision. When the stream issues into the sea it is not difficult to define the western limits since the waters

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of the stream differ in color, temperature, salinity, and flow from the inshore coastal waters. On the east, due to the influx of the Antilles Current, the waters merge gradually with the waters of the Atlantic, and the limits of the stream cannot be fixed with precision. With regards to direction of flow, however, the limits may be fixed to include all waters flowing parallel to the axis but these limits vary with the seasons and with changing conditions of wind and weather.

Recent observations of the Coast and Geodetic Survey indicate that the inner limit of the Gulf Stream as far as Cape Hatteras may be approximately defined as the 50-fathom (91 m) curve.

Considering the outer edge as a line along which the current is still approximately parallel to the axis of the Gulf Stream, the width of Stream northward of its outfall is as follows: off Cape Canaveral about 70 miles; off the coast of Georgia, after its union with the Antilles Current, about 150 miles; off Cape Hatteras about 200 miles.

Off Cape Hatteras the wide-spreading current separates into numerous bands which is indicated by the juxtaposition of warm and cold bands of water of varying width. This feature, though not so marked, is also noticed below Cape Hatteras.

It has been noted that the western or inner side of the Gulf Stream is separated from the coastal waters by a zone of rapidly falling temperature, to which the term "cold wall" has been applied. The abrupt change in the temperature of the waters separated by the cold wall is frequently very striking and is a definite indication of the edge of the stream. It is most clearly marked north of Cape Hatteras, but extends more or less well defined, from the Straits to the Banks of Newfoundland. In the vicinity of the Banks of Newfoundland, the cold wall represents the dividing line between the warm current of the Gulf Stream and the cold waters of the Labrador Current which, according to observations, turns sharply, between parallels 42 and 43 and meridians 51 and 52, and flows easterly, parallel to the Gulf Stream.

Beyond the Banks of Newfoundland the identity of the Gulf Stream, as such, is lost but its general direction is preserved by reason of the prevalence of westerly winds, and its set toward Europe is continued until the continental shores are approached, when, in the vicinity of the Azores, the current divides, one branch flowing to the northeastward and entering the Arctic regions and the other to the south and east in the direction of the African Coast.

As previously mentioned, daily and seasonal fluctuations as to location, velocity, and temperature have been demonstrated as occurring due to winds and variations in barometric pressure and in temperature in the region through which it flows. A further cause of fluctuation is found in the variations of the currents which feed it or which, like the Labrador Current, come in conflict with it. Variations due to tidal currents are now considered as only minor in character.

A steamer bound from Cape Hatteras to Habana, or the Gulf ports, crosses the stream off Cape Hatteras. A fair allowance to