In fome Parts of the Indian Ocean there are periodical Winds, which are called Monfoons; that is, fuch as blow half the Year one Way, and the other Half-Year the contrary Way.

For Air that is cool and dense will force the warm and rarefied Air into a continual Stream upwards, where it must spread itself to preserve the Equilibrium; fo that the upper Courfe or Current of the Air fhall be contrary to the under Current; for the upper Air must move from thofe Parts where the greatest Heat is, and fo by a Kind of Circulation the N. E. Trade Wind below will be attended with a S. W. above, and a S. E. below with a N. W. above: And this is confirmed by the Experience of Seamen, who, as foon as they get out of the Trade Winds, immediately find a Wind blowing from the oppofite Quarter.

In the Atlantic Ocean, near the Coafts of Africa, at about 100% Leagues from Shore between the Latitudes of 28° and 10° North, Seamen conftantly meet with a fresh Gale of Wind blowing from the N. E.

Thofe bound to the Caribbee Iflands across the Atlantic, find, as they approach the American Side, that the faid N. E. Wind becomes Eafterly, or feldom blows more than a Point from the East either to the Northward or Southward.

Thefe Trade Winds on the American Side are extended to 30°, 31°, or even to 32° of North Latitude; which is about 4° farther than what they extend to on the African Side; alfo to the Southward of the Equator, the Trade Winds extend 3 or 4 Degrees farther towards the Coaft of Brazil on the American Side, than they do near the Cape of Good Hope on the African Side.

Between the Latitudes of 4 Degrees North, and 4 South, the Wind always blows between the South and Eaft: On the African Side the Winds are neareft the South, and on the American Side neareft the Eaft. In thefe Seas Dr. Halley obferved, that when the Wind was Eastward, the Weather was gloomy, dark, and rainy, with hard Gales of Wind; but when the Wind veered to the Southward, the Weather generally became ferene, with gentle Breezes next to a Calms

These Winds are fomewhat changed by the Seasons of the Year; for when the Sun is far Northward, the Brazil S. E. Wind gets to. the South, and the N. E. Wind to the Eaft; and when the Sun is far South. the S. E. Wind gets to the Eaft, and the N. E. Wind on this Side of the Equator veers more to the North.

Along the Coaft of Guinea, from Sierra Leona to the Ifland of St. Thomas under the Equator, which is above 500 Leagues, the Southerly and South-weft Winds blow perpetually; for the S. E. Trade. Wind having paffed the Equator, and approaching the Guinea Coaft, within 80 or roo Legues, inclines towards the Shore, and becomes S. S. E. then South, and by Degrees, as it comes near the Land, it veers about to S. S. W. and in with the Land it is S. W. and fometimes W. S. W. This Track is troubled with frequent

Calms, and violent fudden Gufts of Wind, called Tornadoes, blowing from all Points of the Horizon.

The Reafon of the Wind fetting in Weft on the Coaft of Guinea, is, in all Probability, owing to the Nature of the Coaft, which being greatly heated by the Sun, rarefies the Air exceedingly, and confequently the cool Air, from off the Sea, will keep rufhing in to reftore the Equilibrium.

Between the 4th and 10th Degrees of North Latitude, and between the Longitudes of Cape Verd and the Eaftermoft of the Cape Verd Islands there is a Track of Sea which feems to be condemned to perpetual Calms, attended with terrible Thunder' and Lightnings, and fuch frequent Rains, that this Part of the Sea is called The Rains. Ships in failing thefe 6 Degrees have been fometimes detained whole Months, as it is reported.

The Caufe of this feems to be, that the Wefterly Winds fetting in on this Coaft, and meeting the general Eafterly Winds in this Track, balance each other, and fo caufe the Calms, and the Vapours; carried thither by each Wind, meeting and condenfing, occafion the almost conftant Rains.

The lait three Obfervations fhew the Reafon of the two following, which Mariners experience in failing from Europe to India, and in the Guinea Trade. The Difficulty which Ships in going to the Southward, efpecially in the Months of July and Auguft, find in paffing between the Coafts of Guinea and Brazil, notwithstanding the Width of this Sea is more than 500 Leagues: This happens because the S. E. Winds at that Time of the Year commonly extend fome Degrees beyond the ordinary Limits of 4° N. Latitude; and befides, coming fo much Southerly, as to be fometimes South, fometimes a Point or two to the Weft; it then only remains to ply to Windward. And if on the one Side they steer W. S. W. they get a Wind more and more Easterly; but then there is Danger of falling in with the Brazilian Coaft, or Shoals; and if they fteer E. S. E, they fall into the Neighbourhood of the Coast of Guinea, from whence they cannot depart without running Easterly as far as the Ifland of St. Thomas, and this is the conftant Practice of all the Guinea Ships.

All Ships departing from Guinea for Europe, their direct Courfe is Northward; but on this Course they cannot go, because the Coast bending nearly East and Weft, the Land is to the Northward; therefore as the Winds on this Coaft are generally between the S. and W. S. W. they are obliged to fteer S. S. E. or South, and with these Courses they run off the Shore; but in fo doing they always find the Wind more and more contrary, fo that when near the Shore they can lie South; at a great Distance they can make no better than S. E. and afterwards E. S. E. with which Courfes they generally fetch the Island of St. Thomas, and Cape Lopez, where finding the Winds to the Eastward of the South, they fail Wefterly with it, till coming to the Latitude of four Degrees South, where they find the S. E. Wind blowing perpetually,

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On Account of thefe general Winds all those that use the West India Trade, even those bound to Virginia, reckon it their best Course to get as foon as they can to the Southward, that fo they may be certain of a fair and fresh Gale to run before it to the Weftward; and for the fame Reason those homeward bound from America endeavour to gain the Latitude of 30°, where they firft find the Wind begin to be variable, though the moft ordinary Winds in the North Atlantic Ocean come between the South and Weft.

Between the Southern Lats. of 10 and 30° in the Indian Ocean, the general Trade Wind about S. E. by S. is found to blow all the Year round in the fame Manner as in the like Lats. in the Ethiopic Ocean, and during the fix Months, from May to December, thefe Winds reach to within 2° of the Equator; but during the other fix Months, from November to June, a N. W. Wind blows in the Track lying between the 3d and 10th Degrees of Southern Lat. in the Meridian of the North End of Madagascar; and between the 2d and 12th Degrees of South Lat, near the Long. of Sumatra and Java.

In the Track between Sumatra and the African Coaft, and from 3° of S. Lat. quite Northward to the Afiatic Coafts, including the Arabian Sea and the Gulf of Bengal, the Monfoons blow from September to April on the N. E. and from March to October on the S. W. In the former Half-year the Wind is more steady and gentle, and the Weather clearer than in the latter fix Months; and the Wind is more ftrong and steady in the Arabian Sea than in the Gulf of Bengal.

Between the Ifland of Madagascar and the Coaft of Africa, and thence Northward as far as the Equator, there is a Track wherein, from April to October, there is a conftant fresh S. S. W. Wind, which, to the Northward, changes into the W. S. W. Wind blowing at that Time in the Arabian Sea.

To the Eastward of Sumatra and Malacca, on the North of the Equator, and along the Coafts of Cambodia and China quite through the Philippines as far as Japan, the Monfoons blow Northerly and Southerly; the Northern fetting in about October or November, and the Southern about May. Thefe Winds are not quite fo certain as those in the Arabian Sea.

Between Sumatra and Java to the Weft, and New Guinea to the Eaft, the fame Northerly and Southerly Winds are obferved; but the first Half-year the Monfoons incline to the N. W. and the latter to the S. F. Thefe Winds begin a Month or fix Weeks after those in the Chinese Seas fet in, and are quite as variable.

Thefe contrary Winds do not shift from one Point to its oppofite all at once; in fome Places the Time of the Change is attended with Calms, in others by variable Winds; and it often happens on the Shores of Coromandel and China, towards the End of the Monsoon, that there are moft violent Storms, greatly refembling the Hurricanes in the Weft Indies, wherein the Wind is fo vaftly strong, that hardly. any Thing can refift its Force.

All Navigation in the Indian Ocean must neceffarily be regulated by thefe Winds; for if Mariners fhould delay their Voyages till the contrary Monfoon begins, they muft either fail back, or go into Harbour, and wait for the changing of the Trade Winds.

Vapours rifing from the Sea, and by the Wind carried over low Lands to the Ridges of Mountains, and compelled to mount up with the Stream of the Air to the Tops, where the Water prefently precipitates gleeting down by the Chinks and Cliffs of the Stones, and Part of the Water entering into the Caverns of Hills, and gathering into Bafons, which being once filled begin to run over, and form fubterraneous Paffages through the Earth, breaking out in Springs by the Sides of Hills; feveral of thofe meeting together form Rivulets; several of these Rivulets meeting together make a River. This, together with what is incorporated into Vegetables, renders it impoffible for all the Water evaporated from the Sea to return to it again.

Hence the Evaporations arifing from the Mediterranean are fuch, that notwithstanding there are 9 capital Rivers, which empty themfelves into it, befides fmaller ones, there is a conftant Current running through the Straits of Gibraltar from the Atlantic Ocean, to make up the Deficiency. R. Mead, M. D. and F. R. S. obferves, 1. That some Diseases are properly the Effects of the Influence of the heavenly Bodies. 2. That the moft windy Seafons of the Year are about the vernal and autumnal Equinoxes. 3. All the Changes we have enumerated in the Atmosphere do fall out at the fame Times when thofe happen in the Ocean, and, as both the Waters of the Sea and the Air of our Earth or Fluids, are fubject in a great Measure to the fame Laws of Motion, fo that natural Effects of the fame Kind are owing to the fame Caufes. 4. The Alteration made by the Sun and Moon in the Atmosphere must thereby have Influence on the Animal Body. 5. The Elafticity of the Air is of great Moment, and it is reciprocally as the Preffure, fo that the incumbent Weight beng diminished by the Attraction, the Air underneath will be much expanded; thefe, and fuch like Caufes, will make the Tides in the Air to be much greater than thofe of the Ocean; and there is no doubt to be made, but that the fame infinite wife Being, who contrived the Flux and Reflux of the Seas, to fecure that vaft Collection of Waters from Stagnation and Corruption, has ordered this Ebb and Flood of the Air of our Atmosphere with the like good Defign; that is, to preserve it sweet, and a brifk Temper of this Fluid fo neceflary to Life, by a continual Circulation. 6. Two contrary Winds blowing towards the fame Place, may accumulate the Air there, fo as to increase the Height and the Weight of the incumbent Cylinder; in like Manner the Direction of two Winds may be fuch, as meeting at certain Angles, may keep the Gravity of the Airi n a middle State; but if the Winds blow different Ways from the fame Place (which may be occafioned by Thunder and Lightning) the Height and Weight of the Air may be much decreafed. 7. The Changes in our Atmosphere at High Water, New and Full Moon, the Equinoxes, &c. muft occafion Alterations in all Animal Bodies, for all living

Creatures require Air of a determined Gravity to perform Refpiration eafily; for it is by its Weight that this Fluid infinuates itself into the Cavity of the Breaft and Lungs: By a flow Circulation the Secretion of the Spirits is diminished; and, by the Want of the Force of Elafticity and Gravity, the Juices begin to ferment, change the Union of their Parts, break their Canals, and Difeafes follow.

Befides the above Caufes, the Atmosphere may be put in Motion by the elaftic Vapours forced from the Bowels of the Earth by fubterraneous Heats, and condenfed by whatever Causes in the Atmosphere. A Mixture of Effluvia of different Qualities in the Air may, by Rarefaction, Fermentation, &c. produce Winds and other Effects like those resulting from the Combination of fome chymical Liquors; and that fuch Things happen, we are affured from the Nature of Thunder, Lightning, and Meteors. From the Eruptions of Volcanoes and Earthquakes in diftant Places, Winds may be propagated to remoter Countries. The divided or united Forces of the other Planets, and of the Comets, may variously disturb the Influence of the Sun and Moon, &c. We know that there happen violent Tempests in the upper Regions of the Air, when we below enjoy a Calm, and how many Ridges of Mountains there are on our Globe which interrupt and check the Propagation of the Winds, fo that it is no Wonder that the Phænomena we have afcribed to the Ac-` tion of the Sun and Moon are not always conftant and uniform, and that every Effect does not hereupon follow: which, were there no other Powers in Nature able to alter the Influence of, this might in a very regular and uniform Manner be expected from it.

That the rarefied Air afcends is fufficiently demonstrated by the Aeroftatic Globe, or Air Balloon, lately invented; this is a Globe made of Silk, or other light Stuff, made Air tight with Gum; which being filled with inflammable, or rarefied Air, will, when let loose, afcend until it comes to that Part of the Atmosphere that is nearly as light as the Air within it, where it will continue fome Time.

Some of thefe Globes have been made fo large as to carry up Men with them, as have frequently been seen in Britain, France, and other Parts.

NOTE. The Swiftnefs of Wind in a great Storm is not more than 50 or 60 Miles in an Hour, and a common brik Gale is about 15 Hour.

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