Table B to be entered with the declination worked with at the side, and with the hour angle at the top.

When the latitude and declinaton are of the same name, the correction in table B is to be subtracted from that in table A; the result is the correction of longitude for each mile of latitude, and is to be called positive or negative according as the part from table A is greater or less than the part from table B.

When the latitude and declination are of different names, the correction in table A is to be added to that in table B, and the result is the correction of longitude for each mile of latitude, and is always to be called positive.

When the correction is positive, an increase of latitude will make the longitude more to the eastward, and a decrease of latitude will make the longitude more to the westward.

When the correction is negative, an increase of latitude will make the longitude more to the westward, and a decrease of latitude will make the longitude more to the eastward.

Example, shewing the manner of using the tables

Lat. left 34° 16' S.

Lon. left 20° 10′ W.

The day's work to be worked up to the time of sights, and also up to noon, which may always be done before seven bells in the forenoon, as the last hour's run may be guessed quite nearly enough.

Day's work up to the time of taking sights.

The chronometer sights to be worked with the D.R. latitude at time of sights, viz. 32° 18' 48" S. and we will suppose that the longitude resulting is 21° 20′ W. (at the time of sights) apply to this the long run, as usual, and we get lon. by observation at noon 21° 29′ 30′′ W. We then take the corrections from the table, and suppose them to beTable A . . . 38 Latitude and declination Table B

14 J

Correction for each mile of latitude 52 +

different names.

Suppose the lat. observed to be 32° 18′ S. or 14' greater than by D.R., we have—

REMARKS ON THE NAVIGATION of the GULF OF MEXICO, with Notes of Tampico, Tucupan, Vera Cruz, Anton Lizardo, and Tabasco, &c. by Mr. P. Masters, Master Mariner, of Liverpool, 1844.

Ships bound to the Gulf of Mexico through the Yucatan Channel.— Ships, in proceeding from Jamaica and bound to the Gulf of Mexico, should pass to the southward of the Great Cayman in preference to going between it and the Little Cayman, unless there is a good breeze and the position of the ship can be well ascertained before dark, that is, when near the latitude of the Little Cayman, so that the channel can be run through during the first part of the night without risk, as no dependence can be placed on the current about these islands.

Having got to the westward of the Caymans, the course should be shaped so as to pass about mid-channel between Cape Catouche and and Cape Antonio; for if there should be a current running northward NO. 1.-VOL. XV.

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through the channel, it will be found there in its greatest strength. Near the Cuba shore an eddy, or counter-current, often sets round Cape Antonio to the eastward, which will be avoided by keeping as above stated; and it is equally advisable to give the eastern coast of Yucatan a berth, as the soundings are irregular, and can be no guide in ascertaining the ship's position; the coast is also very low, but having got to the westward of Cape Catouche, the soundings are more regular and can be depended on.

Currents between Cape Antonio and Cape Catouche.-The current between Cape Antonio and Cape Catouche, occasionally runs from one and a half to two miles per hour, setting nearly north, or a little to the west of north; in the longitude of Cape Catouche it will be found to make a more westerley course, and about half a degree to the westward of the Cape (on the Campeche Bank) it runs nearly west, but the velocity very much decreased.

Current from Sisal to Laguna and Southern part of the Gulf.From Point Palmas (near Sisal) to the southward of Campeche, there is but little current, and what there may be is influenced by the wind. From Laguna, along the southern shore of the Gulf, it invariably sets along shore to the westward, its velocity being governed by the strength of the land and sea breezes. (The sea breeze generally commences from the N.E. in this part of the gulf, and gradually hauls round as the sun passes to the westward of the meridian, to the east. The land breeze blows from S. to S.E.)

Current on the Western part of the Gulf.-Along the western coast of the Gulf of Mexico the current is also governed by the wind, and an allowance should be made for its drift, in particular, between the latitudes of 24° and 26°.

Currents on the North Coast of the Gulf and West of the Mississipi.-In most of the charts which have been published, the current is described as setting to the eastward, on the north-west coast of the Gulf, (or soundings,) but it is well known by those who have had experience in navigation in this part, that it is erroneous, and that the current most invariably sets to the westward, from the south-west pass to the Mississipi towards the Bay of Galveston, inasmuch that vessels which have been caught to leeward of it, have lost several days before they had made sufficient easting to get a pilot, although the smoke from the steam-boats in the Mississipi has been distinctly seen all the time.

Current east of the Mississipi to the Tortugas.-To the eastward of the Mississipi, there is generally a current setting along shore to the eastward. During a norther (from abreast the Bay of Espiritu Santo and round the Tortugas,) I have found the current setting from two to two-and-a-half miles per hour, to the S.S.E., and striking across the Cuba coast in that direction.

Current setting out of the Gulf of Mexico.-I have occasionally found a narrow stream setting out of the Gulf of Mexico, which has also been experienced by others from whom I have made enquiry. It commences in about lat. 24°, lon. 95°, running towards the E.N.E. to lat. 25°, kon. 91°, from thence to lat. 2510, lon 88°, where it takes a more easterly

direction, and gradually inclining to the south of east as it nears the Tortugas.

Current between Vera Cruz and the Campeche Bank during a norther.—I have been informed by officers in the Mexican navy and masters of merchant vessels who have been in the gulf trade, that in the event of a vessel being caught in a norther off or near to Vera Cruz, when it might be dangerous to run into the anchorage, that by standing to the eastward to about lon. 92° or 93°, a strong set will be found running to the northward, that is, a few hours after the breeze has sprung up; and that ships which have laid to in about the above longitude, have found themselves to the northward of where they were the previous day, owing to the strong set of the current from the southern part of the gulf.

Supposed cause of the current taking the direction as stated in the foregoing remark.-It appears that as the waters of the Gulf of Mexico are so much influenced by the wind, that when it blows strong from the northward it is forced to leeward, and having accumulated to a certain extent, a re-action takes place; that in the first part of a norther, the waters are driven to the southward generally, over the whole gulf, but the current being strongest in soundings, and not having any outlet, it prevents a re-action along the coast, but is forced out to the northward, where there is the least resistance, being where the water is deepest, which is between the coast of Vera Cruz and the western edge of the Campeche bank, in the longitude as before mentioned.

The same theory will also hold good with the south-east winds, which are the most prevalent, and set the waters of the gulf towards the Bay of Galveston, and as the stream from the Mississipi, (particularly the south-west pass), prevents the accumulated waters from making a detour to the eastward along the northern shore of the gulf, a re-action takes place towards the middle of the gulf, which causes, most probably, the eastern current setting out as before stated, varying in its strength in proportion to that of the wind, from three-quarters of a mile per hour, when strongest, but generally less.

Campeche Bank and Alacranes. In running over the northern part of the Campeche bank until the ship is to the westward of the Alacranes, the current will be found in general setting due west, its velocity governed by the wind, both at the time and previous, and also by the strength of the trade wind in the Caribbean and Cuba seas. As at times there is no perceptible current in the Yucatan channel, and consequently but little or none on the Campeche bank.

Alacranes.-The Alacranes are a group of low islands, surrounded by coral reefs, and are very dangerous; on the north side the soundings are no guide to indicate the distance from them. In running to the southward of this group, keep in soundings of not more than eighteen fathoms nor approach the shore so as to shoal the water to less than eight fathoms, which will carry you clear of all danger, except when near the Sisal bank.

Negrillos and Vigias Shoals.-The Negrillos and Vigias shoals, which are laid down in the tracks of vessels bound to Tampico, have been

the cause of ships running unnecessarily a long way to the north. In the directions from the Spanish surveys they are stated as doubtful, and the longitude given varies more than two degrees. It is considered by many that no such shoal exists at the present time. It is quite possible that a submarine volcano may have thrown up a shoal as laid down by the Spanish navigators in the Derrotero, and afterwards been washed away by gales of wind. I have endeavoured to ascertain if there are such shoals, by running down the parallel of latitude in the day time when it could be done without risk, and have not seen the water the least discoloured, and feel convinced that there are no such shoals at the present time, whatever may have been in times past.

Common prudence would keep a person from running on any supposed danger, when it is laid down in the chart, until it is proved to be erroneous. It is certain that a number of vigias, shoals, &c., are laid down in the chart of the Atlantic in particular, and other oceans, which have been placed there on mere supposition alone.

It is very possible that many have been deceived by a wreck floating bottom up, which may have been covered with sea weed and barnacles, and although it may have been struck by a boat-hook or oar, as was done by the Spaniards, as was mentioned in the Derrotero, to what was supposed to be the Negrillos, they may have been deceived, and felt convinced of its being a shoal or reef. Besides, a large body, such as the wreck of a ship, which has been in the water a great length of time and covered with barnacles, &c., would be thoroughly saturated; and if the specific gravity should be but a little less than water, the waves passing with such velocity would scarcely give it a perceptible motion, and in a strong breeze the sea would break over it as if it had been a reef of rocks; and no doubt many such have been reported as reefs, without any further proofs.

With respect to the Negrillos and Vigias, had the Spaniards landed on them and broken off a piece of the rock, or swept it with a line, or sounded round it, and found the water shoal, it would then have been a convincing proof of its being what they stated; but such it appears was not done.

Isla Bermeja.-The Isla Bermeja is also very doubtful. I have made every inquiry about this shoal, and have been informed that neither island nor shoal is now in existence. I have also passed nearly over the position as laid down, and have not perceived the water to alter its colour in the least. It is more than probable that the Isla de Arenas has been taken for the Bermejas, as they are laid down in the same longitude; and as the current is so much influenced by the wind, it is very likely that either by a norther or a strong S.E. breeze, that they may have been out in their reckoning with respect to the latitude.

Isla de Arenas, Triangles, and Los Arcos.-The Isla de Arenas, Triangles, and Los Arcos, are three different groups of islands and shoals; their position, as laid down in the chart of the Gulf of Mexico, may be correct, but they are bad to deal with either in thick weather or night time. The two last groups are of a moderate heighth above the water. The reefs run off from them on their northern side for