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.