origin of several springs immediately from thence, by supposing a subterraneous circulation of waters from the fountains of the

deep.

The Cause of Earthquakes.

EARTHQUAKES are generally supposed to be caused by nitrous and sulphurous vapours, enclosed in the bowels of the earth; which, by some accident, take fire, where there is little or no vent. These vapours may take fire by fermentation,* or by the accidental falling of rocks and stones in hollow parts of the earth, and striking against each other. When the matter which forms subterraneous fires ferment, heat, and inflame, the fire makes an effort on every side, and if it does not find a natural vent, it raises the earth, and forms a passage, by throwing it up, producing a volcano. If the quantity of substances which take fire be not considerable, an earthquake may ensue without a volcano being formed. The air produced and rarefied by the subterraneous fire, may also find small vents, by which it may escape; and, in this case, there will only be a shock, without an eruption or volcano. All inflammable substances capable of explosion, produce by inflammation a great quantity of air and vapour, and such air will necessarily be in a state of very great rarefaction. When it is compressed in a small space, like that of a cavern, it will not shake the earth immediately above, but will search for a passage, in order to make its escape, and will proceed through the several interstices between the different strata, or through any channel or cavern which may afford it a passage. This subterraneous air or vapour will produce in its passage a noise and motion proportionable to its force and the resistance it meets with. These effects will continue till it finds a vent, perhaps in the sea, or till it has diminished its force by expansion.

Mr. Whitehurst imagines that fire and water are the principal agents employed in these dreadful operations of nature.

* Monsieur Lemery, having covered up in the earth about fifty pounds of a mixture composed of equal parts of sulphur and filings of iron, tempered with water, worked into a paste, after eight or nine hours' time, the earth where it was laid,vomited up flames, and caused the earth round it to tremble. From this experiment we see the true cause of the fires of Ætna, Vesuvius, and other burning mountains of sulphur.

SAILING DIRECTIONS

FOR THE

MADEIRAS, CANARIES AND CAPE VERD ISLANDS:

AND FOR

CROSSING THE EQUATOR IN THE ATLANTIC OCEAN.

Directions for the Brazil coast, the Gulf of Guinea, with the Latitudes and Longitudes of the Head Lands, and principal Harbours, as well as Rocks, Shoals and Islands lying in the route to them, from the Equator; with the Winds and Currents at the above places. Drawn from the Observations of Officers of several British East India Company ships. Also particular Instructions for navigating the river Plate. By Captain Haywood.

With some Remarks and Observations of the Author, as well as several other Masters of American ships.

AFTER leaving the English Channel, steer to pass to the westward of Madeira at any convenient distance exceeding 7 or 8 leagues. In winter months it is preferable to pass to the west of Madeira, for strong gales from the westward prevail in November, December, and January, producing eddy winds, and severe squalls near the land; which are occasioned by the high land obstructing the regular course of these gales. In November 1797, and December 1799,* I was each time forced to put to sea from Funchal Road. Severe westerly and S. W. gales, with hard squalls and rain, kept us at sea eight days each time, and prevented us from anchoring afterward, the S. W. wind continuing to blow strong. In these gales, the island of Madeira and the Desertas, were frequently obscured in fog; and the squalls so sudden and violent near the latter, and about the southeast end of the former, as nearly to overset one of the ships in company.f

The principal part of these sailing directions is copied from James Horsburgh's directory, formerly commanding the ship Anna of Calcutta.

Wherever I or we is expressed in the sailing directions, it alludes to Captain Horsburgh. Where an American vessel is mentioned, it is the author's own remark.

November 28, 1797, blowing hard at S. W off the S W. end of Madeira, and a high sea rising, we bore away in the Carron, to endeavour to find shelter under the lee of the island. In running between Madeira and the De. sertas, blowing very hard at S. W. with dark weather and rain, we were sud

PORTO SANTO, in lat. 33° 5' N. long. 16° 16' W., is a high island with several peaked hills on it, about 12 or 14 leagues north eastward from the east end of Madeira, and generally seen by ships bound to the latter: it has a bay on the southwest side, where there is anchorage, water and refreshments; and this road has a rock at its west end, like that of Funchal. Although Porto Santo is not so high as Madeira, it may be seen 12 or 14 leagues from a ship's deck; and is easily distinguished from Madeira or the Desertas, by its Peaks and uneven appearance; these islands having a more regular outline.

The Reef said to lie 3 leagues to the northeast of Porto Santo, on which a Dutch ship was lost, has been found by H. M. S. Falcon to bear about N. 18° W. true bearing, from the body of the island, distant from the nearest part about 7 miles.

The Falcon, Lieutenant J. Bowen, examined this reef, or rocky bank, on the 10th of January, 1802. When the easternmost rock, off the N. E. point of Porto Santo, bore by compass S. E. the N. E. point of Porto Santo S. S. E. E, northernmost rock S. W., and the west point of Porto Santo S. S. W. W. had 22, 23, and 25 fathoms rocky bottom; the master in the cutter, at the same time, about of a mile S. W. from the ship, had 30 fathoms rocky bottom; from whence rowing to the westward the depth gradually decreased to 16 fathoms, and then more suddenly to 12, 8, and 4 fathoms on the shoalest part of the rock, which was plainly discerned from the boat. When she was on it in 44 fathoms, the northeast point of Porto Santo bore by compass S. S E., the northernmost islet or rock S. by W., and the west point of the island S. S. W., distant from the nearest part of it about 7 miles.

This rocky bank extends east and west about 1 mile, terminating in a point of rocks to the westward, on which the least water appeared to be 44 fathoms. Lieutenant Bowen remarks, that when the bearings were taken upon it in the boat, the compass was agitated by her motion, and therefore may not be perfectly correct, but he is certain that the boat was on the shoalest part, otherwise the sea must have broke on it, had there been less water, by the considerable swell and fresh breeze which prevailed

denly becalmed; then followed an eddy wind from N. E., the sea so high as frequently to cover the bowsprit and jib-boom. At this time we were much nearer to Madeira than to the Desertas, with a dark cloud extending over us. At the same time, two ships about two or three miles more eastward, were in clear sunshine, running before a severe squall at S. W.; and one of them had her main topsail blown away. In December 1799, by carrying a press of sail on the Anna, we just cleared the southernmost Deserta, in very thick weather, during one of these westerly storms, which drove us 2 degrees eastward from Funchal. Several outward bound West India ships, were lately dashed in pieces, by running on the Desertas in the night; the effect of an error in their dead reckoning.

at the time. Coming on to blow, he was prevented from making further observations.

With the wind from the northward or N. E., bound to Funchal, the channel between Madeira and the Desertas is the most convenient, and seems about 4 leagues wide from the east point of Madeira to the Flat or Table Deserta, which bounds it to the eastward.

DESERTAS, are high barren rocks, except the northwesternmost, which is level and much lower than the others. The middle Deserta is the largest, between which and the southernmost, called Bogia, there is a narrow channel, never to be attempted unless from necessity, as a ship is liable to be becalmed in it by the northern Deserta, which over-laps the Bogia. The fleet under convoy of H. M. S. Lavinia, bound to India, and to touch at Funchal, passed through the channel between the Middle and South Desertas, in May 1809. They mistook the Desertas for Madeira, and after steering for the south extreme of the large or middle Deserta, proceeded through the channel between it and the southern island, which is 1 or 11⁄2 mile wide at most, and seems perfectly clear of danger. None of the ships tried for soundings, but the fishermen say, that bottom may be got with 60 to 300 fathoms of line, according to the distance from either shore.

The Desertas stretch nearly N. N. W. and S. S. E., rather of an even appearance, and are about 5 leagues in extent. At the N. W. end of the great Deserta, is situated the low small N. W. Deserta, which bounds the channel between these islands and the east point of Madeira. This small level island is seen at 5 or six leagues distance, just appearing above the water, and close to it there is a pyramidal reck, which may sometimes be mistaken for a ship under sail.

MADEIRA is very high and generally clouded, except in serene weather; the east point, which is in latitude about 32° 42′ N. projects out in a kind of peninsula, rather low and rugged, forming an indentation or bay to the southward. In this bay there are soundings laid down in some charts, but they must be very near the shore. In summer, when the N. E. winds prevail, a S. W. current sets through the channel between Madeira and the Desertas and in that season, when the weather is settled, off Funchal valley there are regular land and sea breezes; the sea breeze setting in from S. westward in the forenoon, and the land breeze comes from the shore generally about 10 o'clock at night, but sometimes not till two or three o'clock in the morning. These land breezes do not extend above three or four miles off shore. It has been said, that southerly winds never blow hard quite to the shore at Funchal, that the south

westers or southeasters are never expected, except in January, February, and the beginning of March, and that large ships almost always ride them out; whereas, it is certain, these southerly gales blow quite home to Funchal, sometimes in November and December; and when they are apprehended, it is common for ships of every description to put to sea. These S. W. or S. E. gales, are in general preceded by a swell tumbling into the road, often accompanied by gloomy weather, drizzling rain, and a very unsettled breeze from the land, veering several points backward and forward very suddenly. By such indications ships generally proceed to sea; for should it blow from southward, it would be almost impossible to clear the shore on either tack after cutting or slipping, the anchorage being near the land. Some ships have rode out these southerly gales, but others have been driven ashore.*

In passing through the channel between Madeira and the Desertas, a ship ought to keep at a considerable distance from both; for it would be unpleasant to be drifted near either in calm weather, on account of the want of anchorage. In November, 1797, the Anna drifted in a calm very near the shore to the northward of the Brazen Head, and brought up with the stream anchor in 60 fathoms water, her stern not far from the rocky cliffs. After being at anchor some time, a light breeze from the land, with the help of the boats towing, enabled her to get out of this precarious situation. When a ship has advanced through the channel, and approaching the Brazen Head, she should not keep near it, in case of being becalmed, as there is no anchorage near to this steep bluff point, which is the eastern extreme of Funchal road.

Near this bluff head land, ships are frequently baffled by eddy winds and calms, and obliged to get their boats out to tow: it is therefore adviseable not to borrow too close to it in passing, nor to haul in for the road till nearly abreast of the town. Should a ship enter the road by night, it is proper to show a light at her ensign staff, to prevent being fired at from the forts. In working in with a land breeze, it is best to make short tacks opposite the valley, for here both the land and sea breezes prevail. The Loo rock, situated near the shore, at the west end of the town, is a high rock with a fort on it; and the citadel is a brown square fort on a hill, over the W. N. W. part of the town. The best birth for large ships is the Citadel, a little open to the eastward of the Loo rock, in 30 or 35 fathoms water; the distance from the Loo rock will then not exceed a large half mile.

* A few years ago, several ships at anchor in Funchal road, were driven on shore, and wrecked by one of these gales. This, I think, happened in April or May. The S. W. gales are more frequent at Funchal than any other strong winds.