of Guinea, and the Easterly Trade-winds, blowing to the Westwards thereof, the tendency of the Air here, is indifferent to either, and so stands in Æquilibrio between both; and the weight of the incumbent Atmosphere being diminished by the continual contrary Winds blowing from hence, is the reason that the Air here holds not the copious Vapour it receives, but lets it fall into frequent Rains.
But as the cool and dense Air, by reason of its greater Gravity, presses upon the hot and rarified, 'tis demonstrative that this latter must ascend in a continued Stream as fast it rarifies; and that being ascended, it must disperse it self to preserve the Æquilibrium: that is, by a contrary Current, the upper Air must move from those Parts where the greatest Heat is: So by a kind of Circulation,
the North-East Trade-Wind below, will be attended with a South-Westerly above, and the South-Easterly with a North-West Wind above; that this is more than a bare Conjecture, the almost instantaneous Change of the Wind to the opposite Point, which is frequently found in passing the limits of the Trade-winds, seems to assure us; but that which above all confirms this Hypothesis is the Phænomenon of the Monsoons, by this means most easily solved, and without it hardly explicable.
Supposing therefore such a Circulation, as above, 'tis to be considered that to the Northward of the Indian Ocean there is every where Land within the usual limit of the Latitude of 30, viz. Arabia , Persia , India , &c. which for the same reason as the Mediterranean Parts of Africa , are subject to unsufferable Heats when the Sun is to the North, passing nearly Vertical; but yet are temperate enough when the Sun is removed towards the other Tropick ; because of a ridge of Mountains at some distance within the Land, said to be frequently in Winter cover'd with Snow, over which the Air, as it passes, must needs be much chill'd. Hence it comes