but which did not differ much in point of parallel from that given by bearings pointed out to him during his route eastward.

On the Map*, then, about 1000 geographical miles may be measured on the curvilinear route across the Desert, between the Encampment in El Ghiblah and the Lake Dibbie, whilst the 106 days at ten, give 1060, or sixty more than the Map. It would be useless to reason on the ground of such data; for there seems, from the names and general positions of the Lakes respectively described by Mr Park and Mr Scott, no reason to doubt that they are one and the same, The D is often changed to T, and Tieb or Tee-eb differs little in root from Dib-bie. The 1000 miles give only nine, and somewhat less than a half, instead of ten, for each day.

The Lake, as described to Mr Park, is much smaller than the one seen by Scott; but no one will regard the two accounts as of equal authority. Mr Park says, (p. 213.) Concerning the extent of the Lake Dibbie (or the Dark Lake,) all the information I could obtain was, that in crossing it from west to east, the canoes lose sight of land one whole day." On the other hand, Scott reckons the passage across, twenty-nine hours, at two miles per hour. However, it is difficult to conceive how a vessel, capable of conveying 200 persons across so wide an expanse of water, could be rowed or paddled by the same six persons, at the rate of two miles per hour! Probably, instead of 58 miles, 43 may be a sufficient number. It may be concluded that they crossed it from the N. W. to S. E., as Mr Park's informant told him, that in going towards Tombuctoo, they navigated it from west to east, (in effect in the direction of the general course of the Niger,) and consequently in the line of its greatest length; for river lakes occupying a portion of the valleys or hollows through which the courses of the rivers lie, have their greatest length in those directions. Scott, therefore, may be supposed to have crossed it in the line of its breadth; and it must consequently be a large lake.

He observed no current in the lake, whilst the vessel lay twice at anchor, but her prow pointed to the eastward, although during calm weather. In a lake of that extent, the current of

See the general map of Africa in Mr Park's Travels,

the river would be dispersed, and, therefore, it is difficult to account for the constant position of the vessel. Possibly there might be a light air of wind, but it escaped his notice. There could be no counter current in the middle of so wide a lake. With respect to the report of the boatmen on the lake,—if they could have been supposed to possess any proper knowledge of the future course of the Niger, it would have been worth the the attending to. But having the Shilah for their vernacular language, they doubtless came from the northern quarter of Africa, and were not likely to have any knowledge of the subject, but from report. The opinion of the North Africans has, in all ages, been in favour of its communication with the Egyptian Nile, which probably arises from an idea that it must necessarily reach the sea somewhere. At the same time, it may be remarked, that, in the inland parts of Barbary, there are not less than five considerable streams between Morocco and Tunis, which run inland towards the Sahara, and forming small lakes on its border, are either evaporated or swallowed up by the sands.

In respect of the quality of the soil in the central part of the Sahara, in the line of the before-mentioned route, it may be observed, that in the maps there are two tracts of land in the nature of islands or oases, or, at least, marked as being different from the sandy tract. They are named Gualata and Taudeny. It may well be, that these are parts of the tract described by Scott as being free from sand, and although described to be in a position wide of the route, northward, yet either they may be farther to the south, or the direction of Mr Scott's route may have been more northerly. As he set out in June, when the sun's northern declination was very great, he may not have allowed for it sufficiently in his estimation of the eastern and western points of the heavens. The watered valley in which they sojourned so long, falls very near the western part of Gualata.

It appears that they returned nearly in the line on which they advanced, until they came near this valley, which was about three-fourths of the whole way. But then they evidently deviated; because they traversed the sandy tract in seven days, which took them eleven in their way out, and also came

to a different encampment from the one they had quitted in El Ghiblah.

ART. III.-Remarks on the Currents between the Parallels of Cape Finisterre and the Canary Islands, which may be supposed to have carried the MONTEZUMA out of her course. By Major RENNELL, F. R. S., &c. &c. &c.

I

SHOULD consider myself highly culpable, if I neglected to state, by way of caution to navigators, the result of my inqui ries respecting the current which appear to have caused the shipwreck of the Montezuma, and of a great number of other ships of our own and other nations, on the western coast of Barbary; having examined a multitude of journals of ships that have sailed in that track, with time-keepers on board, and which have also, when opportunities presented themselves, had their rate checked by celestial observations.

The general result is, that navigators who depart from the parallel of the southern part of the Bay of Biscay, (or say 45°,) and sail in the usual track southward, will be assailed first by a SE. current, and then by an easterly one, until they have passed the parallel of Cape Finisterre; when the current will again turn to the south of east, and gradually become a SE. current, till having passed Cape St Vincent, it becomes easterly again; owing no doubt to the indraught of the Strait of Gibraltar; and this easterly current is pretty general across the mouth of the bay between Cape St Vincent and Cape Cantin.

1

Beyond this bay (which may be deemed the funnel, of which the Strait itself is the spout,) the current again becomes SE., or rather more southerly, (as it is more easterly towards Cape Finisterre,) and continues as far as the parallel of 25°, and is moreover felt beyond Madeira westward; that is, at least 130 leagues from the coast of Africa, (beyond which a SW. current takes place, owing doubtless to the operation of the north-east trade-wind).

VOL. IV. NO. 8. APRIL 1821.

The rate of motion of this current varies very considerably at different times, that is, from twelve to twenty or more miles in twenty-four hours. I consider sixteen as rather below the mean rate. I have one example of 140 miles in eight days, in one of his Majesty's ships; equal to 17 miles per day; and in another of only twelve. And in a very well kept East India ship's Journal, 170 in nine days to Madeira, or nineteen per day. The direction of the stream likewise varies, but commonly more towards the south than the east, after passing the mouth of the Strait.

Near the coasts of Spain and Portugal, commonly called the Wall, the current is always very much southerly, owing perhaps to the falling in obliquely on the shore, of the great mass of water brought by the SE. current; which can only run off towards the south, and round Cape St Vincent towards the Strait's mouth. And amongst the Canary Islands, and between them and the coast of Barbary, the currents are less regular. I have endeavoured to describe this in the sketch.

It may be taken for granted, that the whole surface of that part of the Atlantic Ocean, from the parallel of 30° to 45° at least, and to 100 or 130 leagues off shore, is in motion towards the mouth of the Strait of Gibraltar.

According to what has been said in the course of the above remarks, it must be expected that a ship sailing in the usual track to Madeira or the Canaries, will be carried to the southeastward at the rate of sixteen miles per day; that is, even if she has a fair wind, she will be carried by the current 150 or 160 miles to the south-eastward, in the course of her voyage to Madeira or the Canaries; and, consequently, on a SE. by S. course will be carried eighty or ninety to the eastward of her intended port. If we suppose a SE. course, the error in easting will be no less than 109; which distance, if they were bound to Teneriff, would carry them to Allegranza or Fortaventura, and if intending to make Allegranza, would place them or shore on the coast of Barbary. The French and Spaniards report, that their ships have often made Allegranza when they supposed themselves on the line towards Teneriff. It must be added, that if a ship had a long passage, the error would be

greater in proportion, and might possibly amount to 200 miles of easting.

It would seem advisable, therefore, that every ship going to the Canaries, or intending to sail between those islands and the mainland of Africa, and being without time-keepers, as that class of merchant ships commonly are, should, to every day's reckoning, add ten miles of easting. This would, in the first instance, prevent them from deceiving themselves as they went forward; in like manner, as it is better to set a clock forward at once, than to charge one's memory constantly with its being too slow. Ten miles does not seem too much as a cautionary measure, as a ship has very lately been carried ninety-nine miles to the east in eight days in that track. What would not have been the error had she had even a moderately long passage?

It is this current which has furnished the roving Arabs of the desert with their victims from every nation, and the good Mr Willshire with objects of benevolence.

LONDON,

27th February 1819.

J. RENNELL.

ART. IV. On the Submarine Current at the Strait of Gibraltar, and at the Sound near Elsinore *.

IN

N our account of Dr Marcet's experiments on Sea-Water, we have noticed the ideas which are at present entertained respecting the existence of a submarine current salter than the ocean, which runs out at the Strait of Gibraltar, and unloads its waters of their excess of salt. Dr Hudson, in the Philosophical Transactions for 1724 +, seems to have first suggested the probability of this submarine current; and there is reason to think that Lieutenant, afterwards Admiral Patton, had the merit of establishing its existence. When this able officer was Lieutenant of the Emerald, he was overtaken with a very heavy

▪ We have been indebted for the leading facts in this paper to Captain Patton, R. N., the brother of the late Admiral Patton,-D, B.

+ See this Journal, vol. II, p. 339. Note.