The first mariners who approached the Cape of Good Hope were ignorant of the effects of these clouds, which appear to form in the air so slowly, and without any motion, but which in a moment excite the most dreadful storms that precipitate the largest vessels to the bottom of the sea. In the country of Natal, a small cloud similar to the Ox's Eye at the Cape, produces the like effects. In the sea between Africa and America, especially near the equator, these kind of tempests very often arise. Near the coast of Guinea, three or four of these storms sometimes happen in a day; they are also caused and announced by small black clouds; the rest of the sky being generally serene, and the sea perfectly calm. The first blast which issues from these clouds is furious, and would sink ships in open sea, if they did not take the precaution to furl the sails. It is principally in April, May, and June these tempests are experienced on the coast of Guinea, because no regular wind blows there. The stormy season on the coasts of Loango is in January, February, March, and April. On the other side of Africa, at Cape of Gardafu, these kinds of tempests rise in May, and the clouds which produce them are generally in the north like those of the Cape of Good Hope.
All these tempests are produced by winds which issue from a cloud, and which have directions either from north to south, or north-east to south-west, &c. but there are other kinds which are still more violent, and in which the winds seem to proceed from every quarter at once; they have a whirling motion, which nothing can resist. A calm generally precedes these horrible tempests; but in an instant the fury of the winds raises the waves as high as the clouds. There are parts of the sea which cannot be approached, from there being constantly calms and hurricanes in them. The Spaniards have called these places Calms and Tornados; the most considerable are near Guinea, at two or three degrees north latitude; they are 300 or 350 leagues in length by as many in breadth, which forms a space of more than 100,000 leagues square.
When contrary winds come all at once in the same place, as to a centre, they produce whirlwinds by the contrariety of their motions; but when these winds meet with others in opposition, which counterbalance their action, they then revolve in a considerable circle, and occasion a dead calm, through which it is impossible for vessels to make their way. These places of the sea are marked in Senex's globes. I am inclined to think that the contrariety of the winds alone could not produce this effect if the direction of the coasts, and the particular form of the bottom of the sea, did not contribute thereto. I imagine that the currents caused by the winds, but directed by the form of the coasts and the inequalities of the bottom of the sea, end at these places, and that their opposite and contrary direction, in a plain surrounded on all sides by a chain of mountains, is the real cause of these tornados.
Whirlpools appear to be no other than the eddies of the water formed by the action of two or more opposite currents. The Euripus, so famous for the death of Aristotle, alternately absorbs and rejects the water seven times in twenty-four hours. This whirlpool is near the Grecian coast. The Charybdis, which is near the straits of Sicily, rejects and absorbs the water thrice in twenty-four hours. We are not quite certain as to the number of alternative motions in these whirlpools. Doctor Placentia, in his treatise, says, that the Euripus has irregular motions for eighteen or nineteen days every month, and regular ones for the other eleven; that in general it swells about one foot, and seldom two: he says likewise that authors do not agree as to the tides of the Euripus; that some assert it is twice, some seven, others fourteen times in twenty-four hours, but that Loirius having examined it attentively, observed it rose regularly every six hours, and with so violent a motion, that it was sufficient to turn the wheel of a mill.
The greatest known whirlpool is that in the Norway sea, which is affirmed to be upwards of twenty leagues in circumference. It absorbs for six hours water, whales, ships, and every thing that comes near it, and afterwards returns them in the same quantity of time as it drew them in.
It is not necessary to suppose there are holes and abysses in the bottom of the sea which swallow up the waters continually; to assign a reason for whirlpools, it is well known that when water has two contrary directions, the combination of these motions produce a whirling, and seem to form a void place in the centre. It is the same with respect to whirlpools in the sea, they are produced by two or three contrary currents; and as the flux and reflux, which run every six hours in contrary directions, are the principal cause of currents, it is not astonishing that whirlpools, which result from them, attract and swallow up all that surrounds them, and afterwards reject all they have absorbed in the same portion of time.
Whirlpools, therefore, are produced by opposite currents, and likewise by the meeting of contrary winds. These whirlwinds are common in the sea of China and Japan, near the Antilles, and in many other parts of the sea, particularly near projecting lands and high coasts; but they are still more frequent upon land, and their effects are sometimes prodigious. "I have seen," says Bellarmin, "an enormous ditch dug up by the wind, and the earth thereof carried to a distance; so that the place from whence it had been taken appeared a frightful hole, and the village upon which it was dropped was entirely buried with it."
In the history of the French Academy, and in the Philosophical Transactions, are the detail of the effects of many hurricanes, which appear inconceivable and scarcely credible, if the facts were not attested by a great number of intelligent testimonies.
It is the same with respect to water-spouts, which mariners never see without fear and amazement; these are very frequent near certain coasts of the Mediterranean, especially when the sky is cloudy and the wind blows at the same time from various coasts. They are more common near the coasts of Laodicea, Grecgo and Carmel, than in other parts of the Mediterranean. Most of them are large cylinders of water which fall from the clouds, although it appears, when we are at some distance, that the water of the sea rises up to the clouds.[G]
[G] See Shaw's Travels, vol. 2. p. 56.