[B]See Mem. Acad. Sciences, 1721.
[B]See Mem. Acad. Sciences, 1721.
The circumstance of willow leaves being seen in great quantities on the Persian Gulph, and which are supposed by the same authors to come from the Caspian Sea because there are no such trees on the Persian Gulph, is fully as improbable as their subterraneous gulphs, and which Gemelli Careri, as well as the Muscovites, asserts are entirely imaginary: in fact, the Caspian is near one third smaller than the Black Sea, which last also receives much more water by rivers than the former: the evaporationtherefore is sufficient to carry off all its water, nor is it necessary to suppose subterraneous gulphs in the Caspian any more than in the Black Sea.
There are lakes which do not receive any rivers, and from which none go out. There are others which both receive and discharge and some that only receive them. The Caspian Sea, lake Aral, and the Dead Sea, are of the last kind; they receive the waters of many rivers, and contain them. In Asia Minor there is a small lake of the like kind, and one much larger in Persia, on which the town of Marago stands; its figure is oval, and it is about ten or twelve leagues long, by six or seven broad; it receives the river Tauris, which is not very considerable. There is also a similar small lake in Greece, about 12 or 15 leagues from Lepanto, which are the only lakes of that kind known in Asia. In Europe there is not one which is considerable; in Africa there are many small ones, as those which receive the rivers Ghir, Zez, Touguedout, and Tasilet. These four lakes are pretty near each other, and situate towards the frontiers of Barbary near the deserts of Zara; there is another situated in the country of Kovar, which receives the river of Berdoa.In North America, where there are more lakes than in any other part of the world, not one of this kind is known, at least if we except two small collections of water formed by rivulets, the one near Guatimapo, and the other some leagues from Realnuevo, both in Mexico. But in South America, at Peru, there are two contiguous lakes, one of which, lake Titicaca, is very large, and receives a river whose source is not very remote from Cusco, and from which no river issues: there is one smaller in Tucuman, which receives the river Sala; and another larger in the same country, which receives the river Santiago, and three or four others between Tucuman and Chili.
The lakes which receive no rivers, and from which no rivers issue, are greater in number than those just spoken of; these lakes are kinds of pools where the rain water collects; or may proceed from subterraneous waters, which issue in form of springs, in low places, where they cannot afterwards find any drain. The rivers which overflow may likewise leave stagnate waters in the country, which may remain for a long time, and only be replenished by other inundations. The sea has often inundated landsand formed saline lakes therein, like that at Haarlem, and many others in Holland, to which, no other origin can be attributed; or by losing its natural motion, might quit some land, and leaving water in the lowest places may have formed lakes, which have continued to be supported by rains. In Europe there are many small lakes of this kind, as in Ireland, Jutland, Italy, in the country of the Grisons, Poland, Muscovy, Finland, and in Greece. But all these lakes are very inconsiderable. In Asia there is one near the Euphrates, in the desert of Irac, more than 15 leagues long: another in Persia nearly of the same extent, and on which the towns of Kelat, Tetuan, Vastan, and Van, are situated; another small one in Chorazan near Ferrior; another in Independent Tartary, called Lake Levi; two in Muscovy Tartary, another in Cochinchina, and one in China very large, and not far distant from Nankin; this last, nevertheless, communicates with the adjacent sea, by a canal several leagues in length. In Africa there is a small lake of the same kind in the kingdom of Morocco; another near Alexandria, which appears to have been left by the sea; another very considerable one formed by the rain in the desertAzarad, about the 30th degree latitude; this lake is eight or ten leagues long; another still larger on which the town of Gaoga is situate, in the 27th degree; another much smaller, near the town of Kanum, under the 30th degree; one near the mouth of the river Gambia; many more in Congo, about the 2d or 3d degree of south latitude; two more in the country of the Caffrees, one called the Lake Rufumbo, of no great length, and another in the province of Arbuta, which is perhaps the greatest lake of this kind, being about 25 leagues in length by seven or eight in breadth; there is also one of these lakes at Madagascar, near the east side, about the 29th degree of south latitude.
In America there is one of these lakes in the middle of the peninsula of Florida, in its centre is an island called Serope; the lake of Mexico is also of this kind, this is almost round, and about 10 leagues diameter; there is another still larger in New Spain, 25 leagues distant from the coast of Campeachy Bay, and another smaller in the same country near the coast of the South Sea. Some travellers have asserted that there was in the inland parts of Guiana a very great lake of that kind; it iscalled the Golden Lake, or Lake Parima. They have related surprising things of the riches of the neighbouring country, and of the quantity of gold dust that is found in this lake. They give it an extent of more than 400 leagues in length, and 125 in breadth. No river, they say, goes out nor enters therein; although many geographers have marked this lake in their maps, it is not probable there is any such existing.
But the most general and largest lakes are those which receive and give rise to other great rivers: as their number is very great I shall speak only of the most considerable, or of the most remarkable. Beginning at Europe, we have in Switzerland the lake of Geneva, Constance, &c.; in Hungary, the lake Balaton; in Lavonia, a large lake, and which separates this province from Russia; in Finland, the lake Lapwert, which is very long, and is divided into many arms, and lake Oula, which is of a round figure; in Muscovy, lake Ladoga, more than 25 leagues long by above 12 broad. Lake Onega is as long, but not so broad. Lakes Ilmen and Belozo, from whence issue one of the sources of the Wolga; the Iwan-Osero, from whence issues one of the sources of theDon: two other lakes from whence the Vitzogda derives its origin; in Lapland, the lake from which issues the river Kimi; another much larger near the coast of Wardhus, and many others, from whence issue the rivers Lula, Pithea, and Uma. These are not very considerable. In Norway two more of nearly the same size as those of Lapland: in Sweden, lake Vener, which is as large a lake as Meler, on which Stockholm is situated; and two others less considerable; one is near Eveldal, and the other near Lincopin.
In Siberia, in Muscovy, and in Independent Tartary, there are a great number of these lakes, the principal of which is the great lake Baraba, which is more than 100 leagues long, and whose waters fall into the Irtis; the great lake Estraguel, the source of the same river: many other smaller, the sources of the Jenisca; the great lake Kita, the source of the Oby; another larger, the source of the Angara; lake Baical, which is more than 70 leagues long, and is formed by the same river Angara; lake Pehu, from which issues the river Urack, &c. In China and Chinese Tartary, lake Dalai, from whence issues the large river Argus, which falls into the river Amour; the lake ofthe three mountains, the source of the river Helum; the lakes Cinhal, Cokmor, and Sorama, the sources of the river Honaho; two other lakes adjacent to the river Nankin, &c. In Tonquin, lake Guadag, which is very considerable. In India, the lake Chiamat, from whence issues the river Laquia, adjacent to the sources of the rivers Ava, Longenu, &c. This lake is more than 40 leagues broad by 50 long. There is another at the origin of the Ganges; and one bordering on Cashmere is the source of the river Indus, &c.
In Africa is lake Cavar, and two or three others adjacent to the mouth of Senegal river. Lakes Guarda and Sigismus make but one lake, of a triangular form, about 100 leagues long by 75 broad, and contain a very considerable island. In this lake the Niger loses its name, and takes that of Senegal, in the course of which, towards the source, we meet with another considerable lake, called Bournou, where the Niger again loses its name, for the river which comes therein is called Gambaru. In Ethiopia, at the sources of the Nile, is the great lake Gambia, upwards of 50 leagues long. There are also many lakes on the coast of Guinea, which appear to have been formedby the sea, and there are only a few lesser lakes in the remaining part of Africa.
North America may be styled the country of lakes; the greatest are lake Superior, upwards of 125 leagues long by 50 broad; lake Huron, upwards of 100 leagues long by 40 broad; lake Illionois, which, comprehending the Bay of Puanto, is quite as extensive as lake Huron; lakes Erio, and Ontario, together upwards of 80 leagues long, from 20 to 25 broad; the lake Mistasin, to the north of Quebec, is about 50 leagues in length; and lake Champlain, to the south of it, is nearly of the same extent; lake Alemipigon, and the lake Christinaux, both to the north of lake Superior, are also very considerable; the lake Assiniboils contains many islands, and is upwards of 75 leagues long; there are also, independent of that of Mexico, two large lakes in that country, the one called Nicaragua, in the province of that name, which is upwards of 70 leagues long.
In South America there is a small lake, the source of the Maragnon, and another larger which is the source of the river Paraguay; also the lake Titicares, which falls into the river Plata; two smaller lakes which flow into thesame river; and some others, not very considerable, in the inland part of Chili.
All lakes from which rivers derive their origin, those which fall into the course of rivers, and which carry their water thereto, are not salt. Almost all those, on the contrary, which receive rivers without others issuing thereout, are salt; this seems to favour the opinion that the saltness of the sea arises from the salts which rivers wash from the earth, and continually convey into it; for evaporation cannot carry off fixed salts, and consequently those which rivers carry into the sea remain therein. Although river water appears to taste fresh, we well know that it contains a small quantity of salt, and in course of time might have acquired such a considerable degree, as to occasion the present saltness of the sea, and which must still continue increasing. It is thus, therefore, as I imagine, that the Black Sea, the Caspian, lake Aral, &c. have become salt. With respect to lakes, which do not receive any river, nor from which does any issue, are either fresh or salt, according to their different origins; those near the sea are generally salt, and those remote from it are fresh, because the one has been formed by the inundations of thesea, and the others proceed from springs of fresh water.
The lakes any ways remarkable are the Dead Sea, the waters of which contain much more bitumen than salt: it is called the Bitumen of Judea, but is no other than the Asphaltes, which has caused some authors to call it the Asphaltic Lake. The lands which border this lake contain a great quantity of this bitumen; and many have supposed, as the poets feign of lake Avernus, that no fish could live therein, and birds which attempted to fly over it were suffocated; but neither of these lakes produce such mortal events; fish live in both, birds pass over them, and men bathe therein without the least danger.
At Boleslaw, in Bohemia, there is said to be a lake, wherein are holes, whose depth is unfathomable, from which impetuous winds issue, which are carried over all Bohemia, and in winter raise pieces of ice of an 100 weight in the air.
A petrified lake in Iceland is also mentioned; and lake Neagh, in Ireland, has also the same property; but these petrifactions are no other than incrustations, like those made by the water of Arcueil.
ARTICLE XII,
OF THE FLUX AND REFLUX.
Water has but one natural motion; like other fluids it always descends from the higher into the lower places, unless obstructed by some intervening obstacle. When it reaches the lowest place it remains there calm and motionless, at least without some foreign causes which agitates and disturbs it. All the waters of the ocean are collected in the lowest parts of the surface of the earth, of course the motions of the sea must proceed from external causes, the principal of which is the flux and reflux, which is alternatively made in a contrary direction, and from which results a general and continual motion in the sea from east to west. These two motions have a constantand regular relation with the motions of the moon. When the moon is new, or at the full, this motion from east to west is more sensible, as well as that of the tides, which upon most shores ebb and flow every six hours and a half: that it is always high tide whenever the moon is at the meridian, whether above or below the horizon of the place; and low tide when the moon rises or sets. The motion of the sea from east to west is constant and invariable, because the ocean in its flux moves from east to west, and impels towards the west a great quantity of water, and the reflux seems to be made in a contrary direction, by reason of the small quantity of water then driven towards the west; the flux, therefore, must rather be regarded as a swelling, and the reflux as a subsiding of the water, which instead of its disturbing the motion from east to west, produces and continually restores it, although in fact it is stronger during the rise, and weaker during the fall, from the above reason.
The principal circumstances of this motion are, 1. That it is more sensible when the moon is new, or at the full, than in the quadratures: in spring and in autumn it is also more violent than at any other time of theyear; and it is weaker in the solstices, which, is occasioned by the combination of the attraction of the moon and sun. 2. The wind often alters the direction and quantity of this motion, particularly that which constantly blows from the same quarter. It is the same with respect to large rivers which convey their waters into the sea and produce a current there, often extending several leagues, which is strongest when the direction of the wind agrees with the general motion. Of this we have an example in the Pacific Ocean, where the motion from east to west is constant and very perceptible. 3. We must remark that when one part of a fluid moves, the whole mass receives the motion; now in the motion of the tides a great part of the ocean moves in a very sensible manner, and consequently the ocean is agitated by this motion throughout its whole extent.
Perfectly to comprehend this we must attend to the nature of the power which produces the tides. We have observed that the moon acts upon the earth by a power called attraction by some, and by others gravity: this force penetrates through the globe, is exactly proportioned to the quantity of matter, anddecreases as the square of the distance increases. Let us next examine what must happen to the waters when the moon is at the meridian of any one place.—The surface of the waters being immediately under the moon is then nearer that planet than any other part of the globe; hence this part of the sea must be elevated towards the moon, by forming an eminence, the summit of which must be opposite to the moon's centre; for the formation of this eminence the waters at the bottom, as well as at the surface, contribute their share, in proportion to the proximity they are in of the moon, which acts upon them in the inverse ratio of the squares of their distances: thus the surface of that part of the sea is first raised; the surface of the neighbouring parts will be likewise elevated, but to a less height, and the water at the bottom of all these parts will be raised by the same cause; so that all this part of the sea growing higher and forming an eminence, it is necessary that the water of the remote parts, and on which this force of attraction does not act, proceeds with precipitation to replace the waters which are thus elevated and drawn towards the moon. This is what produces the flux, or high tide, whichis more or less sensible on different coasts, and which agitates the sea not only at its surface but even to the greatest depths. The reflux, or ebb, happens afterwards by the natural inclination of the water, for when the moon no longer uses its power, the water which was raised by this foreign power retakes its level, and returns to the shores and places it had been forced to quit. When the moon passes to the antipode, or opposite meridian, the same effect ensues, though from a different cause, In the first case the waters rise because they are nearer the planet than any other parts of the globe; and in the second it is from the contrary reason, they rise because she is the most remote from them; and this it is easily perceived must produce the same effect, for the waters of this part being less attracted than those of the opposite hemisphere, they will naturally recede and form an eminence, the summit of which will answer to the point of the least action that is directly opposite to the moon's station, or where she was thirteen hours before. When the moon arrives at the horizon the tide is ebb, the sea is then in its natural state, and the water in a direct equilibrium; but when she is at the opposite meridianthis equilibrium can no longer exist, since the waters of the part opposite to the moon being at the greatest distance possible from her, they are less attracted than the remaining part of the globe, and hence their relative weight, which always retains them in an equilibrium, impels them towards the opposite point to the moon. Thus in the two cases, when the moon is at the meridian of a place, or at the opposite meridian, the water must be raised nearly to the same height, and consequently fall and rise, when the moon is at the horizon either at her rising or setting. Thus a motion, such as we have just mentioned, necessarily disturbs the whole mass of the sea, and agitates it throughout its whole extent and depth; and if this motion appears insensible in the open seas, it is nevertheless no less real; but as the winds cannot ruffle the bottom in an equal degree with the surface, the motion of the tides is necessarily more regular there, although directed alternately in the same manner as at the top.
From this alternative motion of flux and reflux there results, as already observed, a continual motion of the sea from east to west, becausethe moon, which produces the tides, proceeds from east to west, and successively acting in the same direction, the water follows her course. This motion is most considerable in all sraits; for example, at the straits of Magellan the water rises nearly 20 feet, and continues so for six hours, whereas the reflux lasts only two[C], and the water runs towards the west. This evidently proves that the reflux is not equal to the flux, and that from both there results a motion towards the west, much stronger in the time of the flux than in that of the reflux. This is the reason that in open seas, remote from land, the tides are only felt by the general motion of the waters from east to west.
[C]See Narborough's Voyage.
[C]See Narborough's Voyage.
The tides are stronger in the torrid zone between the tropics than in the rest of the ocean: they are also more sensible in places which extend from east to west, in long and narrow gulphs, and on the coasts where there and isles and promontories. The greatest known flux is at one of the mouths of the river Indus, where the water rises thirty feet. It rises also very remarkably near Malays, in the straits ofSund, in the Red Sea, in Nelson's Bay, at the mouth of the river St. Lawrence, on the coasts of China, Japan, Banama, in the Gulph of Bengal, &c.
The motion of the sea from east to west is more sensible in particular places. Mariners have observed it in sailing from India to Madagascar and Africa; it is also very perceptible in the Pacific Sea, and between the Malaccas and Brazil: but this motion is most violent in the Straits; for example, the waters are carried with such great force in that direction through the Straits of Magellan that it is felt to a great distance in the Atlantic; and it is supposed that this caused Magellan to conjecture there was a strait by which the two seas had a communication. In the Manilla straits, and in all the channels which divide the Maldivian islands, the sea flows from east to west, as well as in the Gulph of Mexico, between Cuba and Jucatan. In the gulph of Paria this motion is so violent that the strait is called the Dragon's Mouth. In the Canadian and Tartarian Seas it flows also with violence, as well as in the Strait of Waigat, through which it conveys enormous masses of ice into the northern seas of Europe. The Pacific Ocean flows from eastto west, through the Straits of Java; the sea of Japan flows towards China, the Indian Ocean flows towards the west, through the Straits of Java and other Indian islands; we cannot, therefore, doubt that the sea has a constant and general motion from east to west, and it is certain the Atlantic flows towards America, and that the Pacific Sea goes from it, as is evident at Cape Current between Lima and Panama.
In short, the alternatives of the flux and reflux are regularly made in six hours and a half on most coasts, though at different hours, according to the climate and position of the lands: thus the sea coasts are continually beaten by the waves which at each time wash away some small parts of their matters, which they transport to a distance, and deposit at the bottom of the sea; so likewise the waves convey, and leave on the lower shores, shells, sands, &c. these by degrees form horizontal strata, which accumulating, become downs and hills, exactly similar to others, both as to form and internal composition. From this constant action, the sea naturally shuts itself out from the lowest coasts, and gains upon the highest.
To give an idea of the efforts of a troubled sea against coasts, I shall relate a fact which has been affirmed to me by a creditable person, and which I the readier gave credit to, having seen something nearly similar. In the principal islands of the Orkneys there are coasts composed of rocks perpendicularly divided to the surface of the sea, to the height of near 200 feet. The tides in this place rise very considerable, as is common in all parts where there are projecting lands and islands; but when the wind is very strong, and the sea swells at the same time, the motion is so great, and the agitation so violent, that the water rises to the summit of these rocks, and falls again in the form of rain: it throws to this great height gravel and stones from the foot of the rocks, and some of them even broader than the hand.
In the port of Livourne, where the sea is much more calm, I saw a tempest in December, 1731, wherein they were obliged to cut down the masts of some vessels that had been forced from their anchors by the wind, and driven into the road. The sea swelled above the fortifications, which were of a considerable height, and as I was on one of the most projecting works, I could not regain the town before I was wettedby the sea-water much more than I could have been by the most plentiful rain.
These examples are sufficient to shew with what violence the sea acts against some coasts. This continual agitation destroys and diminishes by degrees the land. The water carries away all these matters, and deposits them as soon as it arrives at a part where the troubled sea subsides into a calm. In tempestuous weather the water is foul, from the mixture of matters detached from the shore and bottom of the sea, which then casts on the coasts a number of things that it brings from a distance, and which are never met with but after storms; as ambergris on the west of Ireland, and yellow amber on those of Pomerania, cocoa-nuts on the coasts of India, &c. and sometimes pumice and other singular stones. We can quote on this occasion a circumstance related in the new travels to the American Islands. "Being at St. Domingo, says the author, among other things they gave me some light stones, which the sea brought to the coast when there had been strong southerly winds; there was one two feet and a half long by eighteen broad, and one thick, which did not quite weigh five pounds: they are as white as snow, muchharder than pumice, of a fine consistency, having no appearance of being porous, but when thrown into water, rebounded like a ball thrown on the ground, and it was with great difficulty they could be forced under the water with the hand." The stone must have been a very fine and close-grained pumice, which had issued from some volcano, and which the sea had conveyed, as it transports ambergris, cocoa-nuts, common pumice-stone, seeds of plants, rushes, &c. Observations of this kind have been generally made on the coasts of Ireland and Scotland. The sea by its general motion from east to west must convey the productions of our coast to those of America; and it is by some irregular motions that the productions of the East and West Indies, as well as the northern climates, are brought upon our shores. There is a great appearance that the winds cause those effects; large spots have often been observed in the high seas, far from shore, covered with pumice-stones; they could only come from the volcanoes in islands or on the continent, and which the current had transported to the middle of the seas. Before the southern part of America was known, and in the time when the India Sea was thought tohave no communication with our ocean, appearances of this kind afforded the first supposition of it.
The alternative motion of the flux and reflux, and the constant motion of the sea from cast to west, presents different phenomena in different climates, according to the bearing of the land and the height of the coasts. There are parts where the general motion from east to west is not perceptible; there are others where the sea has even a contrary motion, as on the coast of Guinea. But these contrary motions are occasioned by the winds, by the position of the lands, by the waters of large rivers, and by the disposition of the bottom of the sea; all these causes produce currents which alter, and often change the general motion in many parts of the sea; but as the motion from east to west is the greatest, most general and constant, it must also produce the greatest effects, and all taken together, the sea must gain ground towards the west, and lose it towards the east; although it may happen that on those coasts where the west winds blow during the greatest part of the year, as in France and England, the sea may gain on the east, yet these particular exceptions do not destroy the effect of the general cause.
ARTICLE XIII.
OF THE INEQUALITIES AT THE BOTTOM OF THE SEA, AND OF CURRENTS.
The coasts of the sea may be distinguished into three kinds, 1st, the elevated coasts, which are rocks and hard stones, generally divided perpendicularly, and which rise sometimes to the height of 7 or 800 feet. 2d, The low coasts, some of which are almost level with the surface of the water, and others rising with a moderate elevation, often bounded by rocks at the water's edge, forming shelves and breakers, which render the approach to shore very difficult and dangerous. 3dly, Downs, which are coasts formed by sand which the sea accumulates, or brought or deposited byrivers; these downs form hills more or less elevated, according to the accumulated sand.
The coasts of Italy are bordered by several sorts of marble and stone; these rocks appear at a distance as so many pillars of marble perpendicularly divided. The coasts of France from Brest to Bourdeaux are almost surrounded with rocks just at the water's edge, which occasion dangerous breakers. The coasts of England, Spain, and many others, are also bordered with rocks and hard stone; excepting some parts which are made use of for bays, ports, and havens.
The depth of water along the coasts is in proportion to their elevation. The inequalities at the bottom of the sea near the coasts, correspond also with the inequalities of the surface of the ground along the shore. A celebrated navigator has made the following observations on this subject.
"I have constantly remarked, that where the coasts are defended by steep rocks, the sea is there very deep, and seldom affords a probability of anchoring; and, on the contrary, where the ground inclines from the coast to the sea, however elevated it may be furtherinland, the bottom is good there, and consequently admits of anchorage.
"According to the declivity of land, as it approaches the water's edge, so we generally find our anchor ground, and either approach or keep at a distance from shore agreeable to the steepness of the land; for I never saw or heard of a coast where the land is of a continual height, without some vallies lying intermixed with the high-lands; they are the subsiding of low lands, and afford good anchoring, the earth being lodged deep under water; for this reason it is we find good harbours upon coasts which abound with steep cliffs, because the land has subsided between them. But Where the declensions from the hills is not within land but towards the main sea, as at Chili and Peru, and the coasts are nearly perpendicular, as in the countries running from the Andes, it is very deep, and has scarcely any creeks or harbours. The coasts of Gallicia, Portugal, Newfoundland, the islands of Juan Fernando and St. Helena, &c. are somewhat similar to those of Peru, yet good harbours are not so scarce, as there is always good anchorage where there are short ridges of land. In general the land under water seems to be exactly proportionedto the rising of the contiguous part above, and therefore, where the lands upon the shores are steep, there is but little security for ships, they being very easily driven from their moorings; yet although steep cliffs denote this disadvantage, they assure us of this benefit also, that we can sail close to them with safety, besides being able to see them at a considerable distance; whereas low lands are frequently not discovered until we are near, and always experience the hazard of running aground. This fact of good anchorage where the lands on the coast are low, might be illustrated by many instances in the bays of Campeachy, Honduras, Panama; the coasts of Portobella, Carthagena, Guinea, Callifornia, China, Coromandel, &c. but going into particulars would be almost endless, as I very seldom found it otherwise than that deep waters and high shores went together, as well as low lands and shallow seas."
The fact therefore of there being considerable mountains, and other inequalities, at the bottom of the sea is fully confirmed by the observations of navigators. Divers also assure us, there are smaller inequalities formed by rocks, and that it is much the coldest in the vallies ofthe sea. In general the depths in great seas, as we have already observed, increase proportionably to their distance from shore. By Mr. Buache's chart of that part of the ocean between the coasts of Africa and America, and by the divisions he has given of the sea from Cape Tagrin to Rio-Grande, there appears to be similar inequalities in the ocean to those on land. That the Albrolhos, where there are some rocks at the surface of the water, are only the tops of very large and lofty mountains, of which Dolphin island is one of the highest peaks. That the islands of Cape de Verd are also the tops of mountains that there are a great number of shoals in the sea, which round the Albrolhos descends even to unknown depths.
With respect to the quality of the different soils which form the bottom of the sea, as we must rely on divers and the plumb, we can say nothing exact or precise concerning it; we only know that there are parts covered with mud to a considerable thickness, on which anchors have no hold; in these parts probably the mud of rivers are deposited. In other parts are sands similar to those on land. In others are shells, heaped up together, madrepores,corals, and other productions of insects, which begin to unite and appear like stones; in others are fragments of stones, gravel, and often entire stones and marble. For example, in the Maldivian islands the buildings are made of a hard stone weighed up from several fathoms under water. At Marseilles very good marble is obtained from the bottom of the sea, which, so far from wasting and spoiling stone and marble, in our discourse on minerals, we shall prove they are formed and preserved therein; whereas the sun, earth, air, and rain water, corrupts and destroys them.
The bottom of the sea must be composed of the same matters as our habitable land, because the very same substances are contained in the one as the other; places are found at the bottom of the sea, covered with shells, madrepores, and other productions of sea matters, as we meet with on earth an infinity of quarries and banks of chalk and other matters replete with the same sort of shells, madrepores, &c. so that in all respects the dry parts of the globe resemble those covered by the water, both in composition of matters, and inequalities of the superfices.
It is to these inequalities at the bottom of the sea, we must attribute the origin of currents, for if the bottom was equal and level, there would be no other current than the general motion from east to west, and a few others which might be caused by the action of the winds; but a certain proof that most currents are produced by the flux and reflux, and directed by the inequalities at the bottom of the sea, is, that they regularly follow the tides, and change their direction at each ebb and flow. See Pietra della Valle on the subject of the currents of the gulph of Cambay, and the accounts of all navigators, who unanimously assert that in those parts where the flux and reflux of the sea is the most violent, the currents are also most rapid.
Therefore it cannot be doubted but that the tides produce currents whose direction always answers that of the opposite hills and all mountains between which they flow. Currents produced by winds, also follow the direction of those hills which are under the water, seldom running opposite to the wind which produces them, any more than those which are occasioned by the tides follow the direction of their original cause.
To give a clear idea of the productions of currents, we shall first observe they are to be met with in every sea; that some are rapid, and others slow; that some are of great extent, both in length and breadth, and others short and narrow; that the same cause, whether the wind or tides, which produces these currents, frequently gives to each of them a velocity and direction very different; that a north wind, for example, which should give the water one general motion towards the south, on the contrary, produces a number of currents, separated from each other, and very different both in extent and direction; some flowing towards the south, others south-east, and others south-west; some are very rapid, others slow; some long and broad, others short and narrow; in fact, their motions are so various that we have no idea left of their original cause. When a contrary wind succeeds, all these currents take an opposite course, and follow in a contrary direction, precisely in the same manner as would be the case upon land between two opposite and adjacent hills, provided it was covered with water, as is seen at the Maldiva and all the islands of the Indian seas, where the currents run, and the winds blow, for six months in acontrary direction. The same remark has been made on currents between shoals and sandbanks. In general all currents, whether caused by the motion of flux or reflux, or the action by the wind; have the same extent and direction throughout their whole course, yet differ from each other in most respects, which can proceed only from the inequalities of the hills, mountains, and vallies, at the bottom of the sea, it being certain that the current between two islands follows the direction of the coasts; and the same is observable between banks of sand, shoals, &c. we must, therefore, look on the hills and mountains of the bottom of the sea as banks which direct the current; and hence a current is a river, the breadth of which is determined by that of the valley through which it flows: its rapidity depends on the force which produces it, combined with the breadth, of the interval through which it must pass: and its direction is traced by the position of the hills and inequalities between which it must take its course.
We shall now give a reason for the singular correspondence between the angles of mountains and hills, which are to be met with in every part of the world. We have alreadyremarked that when a river, &c. forms an elbow, one of the borders forms on one side a projection inland, and the other forms a point from land, and that through all the sinuosities of their course this correspondence is always found. This fact is founded on the laws of hydrostatics. It would be easy to demonstrate the cause of this effect; but it is sufficient that it is general and universally known, and that all the world may be convinced of it by their own eyes, that when the banks of a river form a projection inland to the left hand, the other shore forms a projection from land to the right.
Hence the currents of the sea must be looked upon as great rivers, subject to the some laws as those on land, and will, like them, form in the extent of their course many sinuosities, whose projections or angles will correspond; and as the banks of currents are hills and mountains, above or below the surface of the water, they will have given these eminences the same form as is remarked on the shores of rivers; therefore we must not be astonished that our hills and mountains, which have been formerly covered by the sea, and formed by the sediments which the waters have left, should,by the motion of its currents, have taken this regular figure, and all the angles are alternately opposite; they have been the shores of the currents or rivers of the sea, and have therefore necessarily taken a figure and direction similar to those of the shores of the rivers of the earth.
This alone, independent of the other proofs we have given, would be sufficient to evince that the earth of our continent and islands have been covered with waters of the ocean, and doubtless throws great light upon the Theory which I have endeavoured to prove well founded; for it was not sufficient to have proved that the strata of the earth were formed by the sediments of the sea; that the mountains were elevated by the successive accumulation of such sediments; and that they were composed of shells and other marine productions; but it required also a reason why the angles of mountains so exactly correspond; this could only be done by an investigation into the real cause, which had not hitherto been attempted, and which, being united with the rest, forms a body of proofs as complete as may be had in physics, and establishes my Theory to be founded on facts, independent of all hypothesis.
The principal currents of the ocean are those observed in the Atlantic Sea, near Guinea. They extend from Cape Verd to the Bay of Fernandes. Their motion is from west to east; that is contrary to the general motion of the sea. These currents are so rapid that vessels sail in two days from Moura to Rio de Benin, a course of 150 leagues; but they require six or seven weeks to return; nor would it be possible to get out of these climates if advantage was not taken of the tempestuous winds which suddenly rise in them; but there are entire seasons during which vessels cannot stir, the sea being continually calm, excepting what arises from the currents, which is always directed towards the coasts, and never extend more than 20 leagues from shore. Near Sumatra there are rapid currents, which flow from south to north, and which probably formed the gulph at Malacca. There are also considerable currents between Java and Magellan, the Cape of Good Hope, and the island of Madagascar, especially on the coast of Africa, between Natal and the Cape. In the Pacific Sea, on the coast of Peru, and the rest of America, the sea moves from south to north, and a south wind continually blowing there seems to bethe cause. The like motion is observed on the coasts of Brazil; from Cape St. Augustine to the Antilles; from the mouth of the Manilla strait to the Philippine islands; and in the port of Kubuxiu at Japan[D].
[D]See Varen. Geography, page 140.
[D]See Varen. Geography, page 140.
There are violent currents in the sea adjacent to the Maldivian islands; and between those islands these currents flow, as already observed, constantly for six months from east to west, and during the other six months they follow the direction of the monsoons, and it is probable they are produced by those winds.
We speak here only of currents, whose extent and rapidity are very considerable, for in every sea there are an infinity of currents, though of no great importance. The flux and reflux, the winds, and all other causes which agitate the waters, produce currents, more or less perceptible, in different parts. We have observed that the bottom of the sea, like the surface of the earth, is overspread with mountains intersected with inequalities and divided by banks of sand. In all mountainous places currents will be violent; in all places where the bottom of the sea is level they will be almost imperceptible; therapidity of the current will increase in proportion to the obstacles the water meets with, or rather to the contraction of the spaces through which they incline to pass. Between two chains of mountains the current will be so much the stronger as the mountains are near. It will be the same between two banks of sand, or two neighbouring islands. It is also remarked in the Indian ocean, which is divided with an infinity of islands and banks, there are rapid currents throughout, which render the navigation of that sea dangerous.
It is not inequalities at the bottom of the sea alone which form currents, but the coasts themselves have a similar effect, as the water is repelled at greater or lesser distances: this repulsion of the waters is a kind of current which circumstances can render continual and violent; the oblique position of a coast, the vicinity of a bay, or of some great river, a promontory; in one word, every particular obstacle which opposes the general motion, will always produce a current. Now, as nothing is more irregular than the bottom and borders of the sea, we must cease from being surprised at the great number of currents which every where appear.
All currents have a determinate breadth, which depends on that of the interval between the two eminences which serves it for a bed. The currents flow into the sea as rivers flow on land, and they produce similar effects. They form their bed, and give to eminences corresponding angles. In one word, it is these currents which hollowed our vallies, formed our mountains, and gave to the surface of the earth, when it was under water, the form it now retains.
If any doubt of the correspondence of the angles of mountains remains, I appeal to the sight of every man who makes the observation. Every traveller, with the smallest attention, will perceive that the opposite sides of a hill exactly correspond. Whenever the hills to the right of the valley form a projection, those opposite recede to the left. These hills have also nearly the same elevation, and it is very rare to see any great inequality of height in the two hills separated by a valley. I can assert, that the more I have looked on the circumference and heights of hills, the more I have been convinced of the correspondence of the angles, and of the resemblance they have with the beds and borders of rivers; and it is by reiteratedobservations on this surprising regularity and resemblance that my first ideas of this Theory of the Earth arose. Let us add to these observations that of the parallel and horizontal situation of the strata, that of the shells being dispersed throughout the earth, and incorporated in every matter; and it must be admitted, that on a subject like this we cannot have a greater degree of probability.
ARTICLE XIV.
OF REGULAR WINDS.
Nothing can appear more irregular and variable than the force and direction of winds in our climates; but there are countries where this irregularity is not so great, and others where the winds constantly blow in one direction, and with almost the same degree of strength.
Although the motion of the air depends on a great number of causes, there are nevertheless principal ones, of which it is difficult to estimate the effects, because of the modifications from secondary causes. The most powerful cause is the heat of the sun, which produces successively a considerable rarefaction in different parts of the atmosphere, and gives rise to an east wind that constantly blows between the tropics, where rarefaction is the greatest.
The force of the sun's attraction, and even that of the moon on the atmosphere, are inconsiderable in comparison with that just mentioned; it is true, this force produces in the air a motion similar to that of the flux and reflux in the sea, yet it must not be supposed that the air, because it has a spring, and is 800 times lighter than water, receives, by the action of the moon, a more considerable motion than that of the waters of the sea; for the distance of the moon being the same, a sea of any fluid matter will have nearly the same motion, because the force which produces it penetrates the matter, and is proportional to its quantity; thus a sea of water, air, or quicksilver, would elevate itself nearly to the same height, by the action of the sun and moon; hence we see that thethe influence of the planets in the atmosphere is not considerable, and although it must cause a slight motion of the air from east to west, this motion is insensible in comparison with that produced by the heat of the sun; but as the rarefaction will be always greatest when the sun is at the zenith, the current of air must follow the sun, and form a constant wind from east to west. This wind blows continually over the sea in the torrid zone, and in most parts of the land between the tropics; it is this wind we feel at the sun's rising; and in general the east winds are more frequent and impetuous than the west; this general wind from east to west extends even beyond the tropics, and blows so constantly in the Pacific Sea, that vessels which sail from Acapulco to the Philippines, perform their voyage, which is more than 2700 leagues, without any risque, and almost without any need of directing their course. In the Atlantic, between Africa and Brazil, this wind is also constant: it is felt also between the Philippines and Africa, but not in so constant a manner, by reason of the islands, and different obstacles that are met with in that sea; for during the months of January, February, March, and April, it blows betweenthe Mozambique coast and India, but during the other months, it gives place to different winds: and although this east wind is less felt on the coasts than in the open sea, and still less in the middle of continents than on the coasts; nevertheless there are places where it blows almost continually, as on the east coasts of Brazil, on the coasts of Loango, in Africa, &c.
This east wind continually blowing under the line, is the cause, that sailing from Europe to America, the course of the vessel is directed from the north to the south, along the coasts of Spain and Africa, to within 20 degrees of the equator, where this east wind is met with, which carries them directly to the coasts of America. The voyage from Acapulco to the Philippine islands, is made in two months by the favour of this east wind: but the return from them to Acapulco is longer and more difficult. At 28 or 30 degrees on this coast from the line, the western wind is nearly as constant, which is the reason that vessels returning from the East Indies to Europe, do not follow the same track as in going; those from New Spain sail north along the coasts till they arrive at the Havannah, and from thence they continue northward,until they meet with the westerly winds which carry them to the Azores and afterwards to Spain. So likewise in the South Sea, those which return from the Philippines, or China, to Peru, or Mexico, sail north as far as Japan, and navigate under that parallel to a certain distance from California, from whence, coasting along New Spain, they arrive at Acapulco. These winds do not always blow from one point, but in general from the south-east from April to November, and from the north-east from November to April.
The east wind, by its action, increases the general motion of the sea from east to west; it also produces currents which are constant, some flowing from east to west, others from west to east; and from the east to the south-west or north-west, following the direction of the eminencies and chains of mountains at the bottom of the sea, the vallies that divide them serving as channels to these currents. The alternative winds which blow sometimes from the east, and sometimes from the south, produce also currents which change their direction at the same time with these winds.
The winds which blow continually for some months, are generally followed by contrarywinds, and therefore mariners are obliged to wait for that which is favourable to their voyage. When these winds change, a calm or dangerous tempest generally ensues, and which continues for several days, sometimes a month, and has been known for more than two.
These general winds caused by the rarefaction of the atmosphere, are differently combined and modified by different causes in different climates. In that part of the Atlantic, under the temperate zone, the north wind blows almost constantly during the months of October, November, December, and January, which makes those months the most favourable to embark from Europe to India, in order to pass the line by the aid of these winds; and it is known by experience, that ships which quit Europe in the month of March frequently do not arrive sooner at Brazil than those which sail in the October following. The north wind almost continually reigns during winter in Nova Zembla, and other northern coasts. The south wind blows during the month of July at Cape de Verd, when the rainy season, or winter of these climates sets in. At the Cape of Good Hope the north-west wind blows during the month of September. At Patna,in the East Indies, the north-west wind blows during the months of November, December, and January, and produces heavy rains; but the east wind blows during the other nine months. In the Indian ocean, between Africa and India, as far as the Malacca islands, the monsoons reign from east to west from January to the beginning of June, the west winds begin in the months of August or September; during the interval of June and July, there are dreadful tempests generally from the north winds; but on the coasts these winds vary much more than in the open sea.
In the kingdom of Guzarat, and on the coasts of the neighbouring sea, the north winds blow from March till September, and during the other months south winds almost always reign. The Dutch, to return from Java, generally set sail in the month of January or February, when they have the assistance of an easterly wind which is felt as far as the 18th degree of South latitude; afterwards they meet with the south winds which carry them to St. Helena[E].