WINDS.
The Winds, different from our Quarter of the World, in these Voyages are either peculiar to warm Latitudes; such are Trade-Winds, Land and Sea Breezes; or to the Coast, Tornadoes, and Air-Mattans.
Trade-Winds are easterly, blow fresh night and day, all the Year, and every where round the Globe; that Part of it I mean that we are upon, the Ocean, whether Atlantick, Indian, or American: for the Soil and Position of Lands, though the same Cause of them subsists more powerfully, gives uncertain and various Deflections. They will extend to 30°° of N. Latitude, when the Sun is on this side the Equator, and as far S. when on the other; deflecting where he is farthest off (here to the N. E. there to the S. E.) and always nearest to the E. Point on the Equinoctial, or where he is vertical.
The general Causes assigned by the Ingenious for these Phænomena, and with the greatest Probability of Truth, are;
First, the daily Rotation of the Earth Eastward upon its Axis, whereby the Air or Wind (the enforced Stream of it) by this means goes Westward in respect of the Superficies; and this is farther countenanced in that these Winds are found only in the largest Circles, where the diurnal Motion is swiftest; and also because they blow as strong in the Night as Day; home, on the Coast of Brasil, as near Guinea.
The second permanent Cause of this Effect, the ingenious Dr. Halley ascribes to the Action of the Sun-beams upon the Air and Water every day, considered together with the Nature of the Soil, and Situation of the adjoining Continents.
The Sun heats and rarefies the Air exceedingly, in all Latitudes within the Zodiack, (evident from the anhelous Condition it subjects most Animals to in Calms) and therefore the Air from Latitudes more without his Influence (as more ponderous) presses in, to restore the Equilibrium: and to follow the Sun, must come from the Eastward. The westerly Winds that restore this Balance, from Latitudes beyond the Tropicks, would, I fancy, be as constant, and keep a Circulation, were the whole a Globe of Waters: As it is, they are from 30 to 60°°, abundantly the most predominant, with a Deviation to N. or S. on various Accidents: blow with more force, because, among other Reasons, the Equilibrium is restored to a greater from a lesser Circle; and as it were to confirm this, are received into the Trade-wind, with a Deflection of N. E. or more northward at the Point of reception.
On the Coast of Guinea, North of the Equinoctial, the true Winds are westerly, keeping a Track with the Shore, where it trenches all eastward. From the River Gabon again, under the Line, the Land stretches to the Southward, and, exactly answerable thereto, the Winds wheel from S. E. to S. by E. to keep nigh a Parallel with it; in both, the Shore seems to deflect the true Trade, in the same manner Capes do Tides or Currents, and obliges it, like them, on that Point where they have the freest Passage. If at any particular Seasons (as in the Rains is remarked) the Winds become more southerly, and set full upon the Shore, they are weak; and as the Sun is at such time on this side the Equinoctial, it is probably to restore an Equilibrium to that Air at land, more rarefied from a stronger and more reflected Heat.