is much weaker than that from the south; and therefore the passage round Africa, from the Red sea to the Mediterranean, appears at every step, as we advance in the inquiry, to have been an easier task than a different order of proceeding.

In the open sea, between the island of Madeira and the south-east trade, the velocity does not appear to exceed 10 to 14 miles per day; but in approaching the land of Cape Blanco, it is found to be in some places 24. Along the coast of Guinea it varied from 30 to 10, or 17 at a medium: and on that of Serra Leona (or Western Guinea), it was about 12 southward, during the northerly monsoon; eight or nine northward, during the opposite one; reckoned at a medium of the northern and southern sets, during the number of days that the ships were exposed to it. But it is proper to observe, that no degree of current was observable between the parallel of 10o, and that of the mouth of the Gambia, in either season; which still water appears to be owing to the form of the land of Cape Verde, which throws the current so wide into the ocean, as to prevent its return in any shape, so as to disturb the quiet of the sea, to the distance of several degrees beyond it. And it may be remarked, that within the space subject to periodical winds and currents, the extensive cluster of islands and shallows, named Bissagoes, and also those of St. Anne, are found 8.

8

Although the motion of the sea be, on the whole, more to the north, in one season, and to the south in the other; yet so near the shore as a coasting vessel would navigate, the tide has a considerable influence. In the offing, some of the old naviga

Cape Blanco occasions a similar degree of quiet in the bay of Arguin, which lies to the SE of it. There also islands and shallows are accumulated to a great extent: and the current does not close with the shore for 50 or 60 leagues; but it evidently comes in to the north of the river Senegal; since the singular deviation in its course, near the sea, is the effect of a southerly current, which has hurried its depositions lower and lower down.

The singular form of Cape Verde is no doubt owing to the general current on the north, and the counter current on the south, which have corroded the land on both sides, until nothing remains, save the sharp termination of the base of the great mountainous belt of North Africa. Concerning the effect of the obliquity of the current, occasioned by it, we have just spoken: but it may also be proper to mention, that, as the conformation of the land affects the water below, so it does the atmosphere above: for the trade winds during the winter of the northern hemisphere, are inflected by it, from NE to NW.

These are the general outlines of the streams of current in the south and east parts of the Atlantic; and which, to explain in a detailed manner, would require a volume. It is highly probable that the seasons may occasion a very considerable degree of variation, in the length, and perhaps also in the

tors have remarked, that the currents are very uncertain and distracting. Possibly a part of this seeming uncertainty arose from bad reckonings; for in the modern reckonings, checked by time-keepers, and good observations of latitude, the currents appear pretty regular here.

breadth of the three principal streams; that is, the northern and southern; and the equatorial current, formed by the confluence of the two first: but there is no reason to suppose that any alteration takes place in their line of course. As for the particular veins of current that are derived from the main streams, and which conform to the indentings of the coast, there is no question but that great changes take place, as well in their courses, as in their velocities, in such places as are subject to the influence of periodical winds and of tides. We trust that the length of this discussion will be pardoned on the score of its applying as much to the business of modern navigations, as to the elucidation of ancient ones.

From the result of this inquiry, it appears, that our circumnavigators, who could have navigated the coast from the bay of St. Thomas to Senegal, only in the seasons of the NE winds, or of the sea and land breezes that prevail in the winter of the northern hemisphere, must have had, generally, an adverse current as far as the Bissagoes; and again, every where to the north of Cape Verde, (the bay of Arguin excepted) as far as Cape Cantin. Moreover, that from the Senegal river, to the end of the NE trade, the wind, as well as the current, was against them; so that the latter part of the passage through the ocean, must have been tedious indeed. We return to the consideration of the detail of the voyage.

The beginning of November has been fixed as the earliest time of moving westward; and the dis

tance, following the windings of the coast, has been taken at 39 degrees (of a great circle). It has been stated in page 390, sup. that they were opposed by currents of different degrees of strength, and also that there is a space (about five degrees) on the south of Cape Verde, where the sea is still. Therefore the impediment, calculated at a medium throughout, may be taken at 13 miles per day.

It has also appeared that 35 miles was the medium rate of sailing of the ancient ships (see page 360 sup.); from which, 13 being deducted, leaves 22 for the net progress. But even from this, there are to be deducted all kinds of delays, whether casual, or growing out of the ordinary wants of the crews, and also accidents; so that it is probable, that no more than 18 can be allowed for the regular and constant progress: and, it may be remarked, that Nearchus advanced at no greater rate than 22 per day through the ocean; although no current is supposed; and very often 17 was the result of a hard day's work".

The 39 degrees, at 18 per day, require 130 days, or upwards of four calendar months: so that they could not arrive at the river of Senegal before the beginning, or towards the middle, of March.

Here we may conceive the navigators to have been again within the sphere of their knowledge; on a supposition that this part of the coast had been already explored, in a general way, either by the

It is proper to remark that the rate of Nearchus is founded on the number of sailing days; had it been on the gross number, it would have been still lower.

Egyptians or Phoenicians: and that they would be apprised, in consequence, of their relative position to the pillars of Hercules, and to their native country.

According to the foregoing calculation, they had been about 19 months, or more, from the head of the Red sea, when they arrived in the Senegal river; and might yet have a voyage of five months to perform, in order to complete their circumnavigation. For although the distance from the Senegal to the mouth of the Nile, along the coast, in the usual way, does not exceed 57 degrees, yet they had to contend (as we have shewn) with an adverse trade wind, as well as a current, propagated by it, during the first part of their voyage from Senegal homewards; and which, from these circumstances, may perhaps have been the most arduous part of the whole. And it may also be supposed, that, waiting the September harvest, at the Senegal river, they could not profit so much from the land and sea breezes, as at an earlier period.

The space occupied by the still water in the bay of Arguin, &c. being deducted, 10 or 11 degrees remain, of a navigation, impeded by an adverse current; and where the wind, although subject to inflexions, from the alternate influence of the land

1 The existence of this current, which is allowed on all hands, is proved by the error of Hanno, who calculated that Cerné, (Arguin) was just as far to the south of the Straits, as Carthage was to the east of it. The difference, which is very considerable, is occasioned by the current, of which Hanno appears to have been ignorant; he calculating merely by the ship's reckoning. More will be said concerning it in the next Section.