several miles, on which many vessels have been wrecked. For further particulars see the Book of Directions and Charts last published.

Baxo Nuevo.-The Baxo Nuevo, which is laid down on the charts, to the S.E. of the Isla de Arenas, and in the track to Vera Cruz, has been reported to have been seen about five or six years since, and said to be a very dangerous shoal. I was informed by an American captain that when he was in Vera Cruz, a French brig had arrived, and that he had run down between the Alacranes and the land, with a moderate easterly breeze, and all sail set. He had got so far to the westward that he expected to pass between the Isla de Arenas and the Triangles, at about mid-channel, and considered himself sufficiently to the south of the Baxo Nuevo, by the course he had steered, that should there be such a danger he would avoid it. Having had a good meridian altitude, and ascertained his longitude, by chronometers (which was afterwards found to have been correct,) he considered they were in a fair way for running off the Campeche soundings. Towards evening they saw heavy breakers ahead, running very high, when they immediately shortened sail and hauled the vessel on a wind, by which time they were close up with the shoal. They sounded and found but little water (I am not quite certain, but I think it was twelve fathoms, sandy bottom,) he then stood to the southward, until he had deepened the water, when he again shaped his course for Vera Cruz, and by sights which he took afterwards, he found he had been set a great way to the north,* from which he considered the shoal must have been the Baxo Nuevo, or that the Isla de Arenas was wrongly laid down in the chart.†

Baxo de Obispo.-The Baxo de Obispo may have been seen, but I never heard any one either to confirm or contradict its being in existence. It is best to give it a good berth.

Sisal Bank.-For the directions and the soundings, &c., on and about the Sisal bank, see the last publication of "Directions for the Gulf of Mexico."

Vessels bound to Tampico from the Carribbean Sea.-In all seasons of the year, the most preferable course to take, when bound to Tampico, is, that after having obtained soundings on the eastern edge of the Campeche bank, to run down the latitude of 23°, or in the season of the northers 23° 30'. The soundings will be then upwards of forty fathoms of fine sand and shells, and in general with black specks, and between longitude 87° and 88° with patches of red and white coral.

Having got to the westward of the Negrillos, as laid down in the chart, with the wind from the eastward, the course should be shaped for the bar of Tampico, and when about a day's sail from the coast, to run down in

The wind had no doubt been blowing from the S.E. which would cause a current setting from that quarter, and would cause the ship to be north of the reckoning.

+ The sights of the stars, if not taken both north and south of the zenith for the latitude, and east and west of the meridian for time, and the means of them taken, would be liable to a great error, caused by the false horizon, which is very general in low latitudes in the night time, through the haze which hangs over the sea.

the latitude of the bar. But if the wind should be either to the northward or from the south of east, care should be taken to keep to windward of the port, as the current in shore very often runs strongly, influenced by the wind, and has been the cause of many vessels lying outside in a norther, when had the land been made to windward they might have got a pilot and entered the port.

Ships bound to Vera Cruz.-A vessel bound to Vera Cruz from the Cuba sea having passed through the Yucatan channel and got soundings on the Campeche bank, can run along shore with safety, by keeping in not less than eight fathoms water, and not increasing the depth to more than eighteen fathoms; this will carry her clear of the Alacranes in the offing to the northward, and the sand heads along the coast, but on approaching the meridian of Sisal she should be kept more off shore, so that the soundings should not be less than eleven fathoms, which will carry her clear of the Sisal shoals.

From abreast of Sisal, the best channel is by running between the Baxo Nuevo and the Triangles, care being taken to give the shoals under the lee the widest berth, particularly with the wind from the north when the current will be setting to the southward, but its strength being influenced by the time it has been blowing. As the shoals about the Triangles extend some distance from the islands as has been already stated, and the soundings being such that the position of the vessel cannot be depended on, an allowance for the set of the current should be made.

With a south-east or a southerly wind, the current is not so strong as when the wind is from the north, yet it would be advisable with the wind from this quarter, to give the Baxo Nuevo the widest berth.

Ships bound to Campeche, Laguna, or Tobasco.-Ships from the eastward, bound to either Campeche, Laguna, or Tabasco, by keeping in soundings as before stated, when on the north coast of Yucatan, would be in the general track; but in the season of the northers the land should be given a wider berth, nor shoal the water to less than sixteen fathoms, in case the wind should spring up from that quarter, so that there would be sufficient offing to weather the Sisal shoals; having run the distance of these shoals and deepened the water, the course can be shaped aceordingly. If bound so far to the westward as Tabasco, by running inside Los Arcos, that is, to the eastward of them, would be most advantageous, as there is less sea in soundings in a norther than in the middle of the gulf, and with the wind from the south-east or easterly she would be to windward of the port.

It is to be observed, that in the Campeche soundings, the norther seldom or never blows any thing near so strong as it does along the western side of the gulf, or even off soundings, so that the vessel can be kept to windward under easy sail, ready to bear up for the intended port, as soon as it moderates; and in fine weather advantage can be taken of the land and sea breezes.

Sailing from Tampico or Vera Cruz for New Orleans or Europe. In sailing from Tampico or Vera Cruz, bound to New Orleans or out of the Gulf of Mexico in the season of the northers, it is best to run into the latitude of 25° as soon as possible, without much regard to lon

gitude, that is, to keep the ship a good clean full when the wind will allow her to clear away the land on the starboard tack; having reached this latitude she will be in a good position for a north, and besides, if there is any current setting out of the gulf it is most likely to be fallen in with. (See currents in the Gulf of Mexico, already stated).

Sailing from Laguna or Tabasco out of the Gulf.-From Laguna or Tabasco it is most advisable to keep on the Campeche bank in all seasons of the year, running inside Los Arcos and the Alacranes, and after reaching the longitude of 89°, if the wind should be easterly, to stretch off to the northward, to the latitude of the Tortugas, which will be in a good position for any change of wind.

For making the land about Tampico, see "Coasting Directions from Isla de Lobos to the Bar of Tampico," published in the Nautical Magazine, in January, 1834, which has also a chart of the river Panuco.

Bar of Tampico.-As the bar of Tampico is liable to shift more or less with every gale of wind, there can be no guide laid down for entering the river; but as soon as the bar is passable, the pilots will be off, and should there be sufficient water on the bar, they will probably take you in; and, if not, there is no alternative but to lighten the vessel by discharging part of the cargo, which tends to a heavy expense.

Discharging cargo outside the bar.-If any of the cargo is discharged outside the bar, the vessel (when she gets inside) has to be brought to an anchor, abreast the south pilot establishment, to receive it on board again; but vessels whose draught of water will allow them to go over the bar without discharging outside, as soon as they are in the river, are boarded by the captain of the port, and custom-house boats, who receive the ship's papers and letter-bag, (for which the captain should have a receipt,) the hatches, and all communication with the hold is sealed up, after which she can proceed up to the town; an officer in general goes up with her.

Proceeding up from the bar to the town.-When the vessel is inside the bar, and at the anchorage abreast the pilot establishment, the pilot takes no more charge, and leaves her; but as the water is deep, there is danger to be apprehended in proceeding up, the larboard or southern shore should be kept aboard, as on the opposite shore the water is shoaler; and when abreast of Paso de las Piedras (see map of the bar and river in the Nautical Magazine for January 1834,) the larboard shore must be approached as near as possible, to avoid the long spit which runs off from the point. When abreast of the entrance to Pueblo Viejo haul gradually over to the custom-house wharf, and come to an anchor as near as possible for the purpose of discharging the cargo.

Fort at the bar.-On the north side of the entrance of the river is a small fort, with a few guns mounted on it. Before vessels are allowed to sail, a clearance must be had from the custom-house, which has to be delivered to the commandante, or the officer in charge. Near the fort is a vigia, or lookout, and a telegraph, from which signals are made to the town, when any sail is in sight, the state of the bar, &c.

(To be continued.)

BARS OF RIVERS.

THE Construction of harbours of refuge, and also the best methods of improving the state of those already existing, occupying, at the present day, no inconsiderable share of public attention; I trust that I may be excused, in sending a few remarks, on the laws which govern the movements of shingle beaches, in connection with an endeavour, to investigate into the cause of the existance of bars across the entrance of some navigable rivers, when others remain entirely free from such an obstruction.

An on-shore gale propels a shingle beach along a line of coast, in the direction from which it blows, and at the point where this shingle drift crosses the entrance of a harbour we meet with a bar.

But where a river like the Thames discharges its waters into an estuary, which gradually widens towards the sea, the travelling beach will follow the line of coast, forming the sides of the inlet; since where the estuary becomes narrow, the oceanic waves will lose their transporting power; and so from the shingle being deposited along its shores, no bar will be accumulated across the mouth of the river.

It has been urged in opposition to this theory: "that if bars are occasioned by the progressive movement of a shingle drift during an onshore gale, they would rapidly diminish, or wholly disappear, in calm weather, or when the wind blows from the shore; and that the navigation would be wholly obstructed, by the sudden increase of the bar, in an on-shore gale.”

I am ready to admit that such might be the case, if there was not another agency at work which counteracts this tendency. A breeze of wind blowing from the shore causes the shingle beach to accumulate, which prevents the scouring action of the river or tidal waters from diminishing the bar. On the other hand, an on-shore gale, while it imparts a progressive motion to beach, it at the same time returns the shingle in a seaward direction, and effectually checks any tendency which might otherwise exist, of a sudden increase of shingle on the bar.

The cause of these alternate movements of the shingle beach may be thus explained. A breeze of wind, blowing across an expanse of water raises its surface to the leeward. This produces an under current in the opposite direction, by which the equilibrium is restored. In an on-shore gale this under current will be in a seaward direction, and will carry with it the shingle from the beach. In an off-shore wind, this under current will set in towards the shore, and cause the shingle to accumulate again. Sometimes these results may follow a change of wind in the offing, when it does not reach the shore.

If we consider the velocity necessary to give a tidal current a sufficient impetus to set in motion a travelling beach, it must appear self-evident that too much has been ascribed to mere tidal agency by the many who have endeavoured to investigate the cause of this phenomenon, which may be attributed to the circumstance,that in general, the set of the flood tide being from the open sea, it thus coincides in direction with that of the

gales of wind which raise the heaviest waves, which, consequently, give to the movements of the shingle beach its predominating impulse; but an attentive observer will perceive that an on-shore gale, from an opposite quarter, will cause the beach to move in a direction contrary to that of the flood tide. A rocky coast presents a conformation unfavourable to the accumulation of a shingle beach, from the circumstance that the waves, in their recoil, run back with augmented force through the hollows between the rocks; thereby returning in a seaward direction, any shingle that might otherwise have been accumulated by the impinging billow.

But we have reason to suppose that the progressive movement of the beach, is maintained past the ends of the rocks, in a continuous line, in some instances, at a considerable depth below the surface of the water; since, as soon as the configuration of the coast, favours an accumulation in-shore, the beach is again visible, the waves of the sea appear to possess an upheaving power to a considerable depth. The shore in the

neighbourhood of some of the northern coal ports, are covered with flint and gravel, which can only have been derived from the ballast thrown out of vessels at sea; which ballast is not allowed to be deposited at a less depth than five fathoms at low water.

If we admit that travelling beaches owe their progressive motion to the impinging force of the oceanic billows, we must expect to find that as the line of coast becomes more sheltered from the violence of the prevailing gales, and as a necessary consequence, the transporting power of the waves decreases, that the movement of the shingle beach will become slower, and the tendency to accumulation greater. The southern shores of England, to the east of the Isle of Wight, and the coast of Suffolk, may be adduced as examples in confirmation of this position, the latter locality being protected by the sand banks lying off the coast.

We now come to the important question as to how far it is probable that the proposed harbours of refuge will be encumbered with accumulations of shingle at their entrances. To begin with Dover :-It is proposed, in the first place, to run out a pier, in order to arrest the onward progress of the shingle, and thereby to protect the present harbour. We will suppose that this is done, and an entrance 700 feet broad, as proposed is made on the south side of the new harbour; and that the south pier does not over-lap the other, to protect the entrance. In this case, the shingle will accumulate behind the first pier, until the angle behind it is filled up; when it will wash into the harbour, and be deposited at the point, where, from the shelter of the breakwater, the waves lose their impinging power. And should no measures be taken in the interim to remove it, this shoal will continue to increase until its surface reaches to the high water mark, and the entrance to the harbour is wholly blocked up, and then the shingle will pass along outside of the pier, until it meets with another obstruction. But if the piers are made to over-lap, so that the shingle may pass from the outside of the one to the outside of the other, it will merely form a bar across the entrance, and in this case the works should be so constructed, as to cause the NO. 1.-VOL. XV.

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