CHAPTER XXXXIV.
Depressing Columns of Air known to the Egyptians.
Section 239. THE Existence of depressing Columns of Air was well known to a People more ancient than either Romans or Greeks.
240. The sultry Climate of Egypt, whose Situation is that of an extensive Meadow watered by a broad River, and enclosed by Mountains to the East and West; consequently not subject to general horizontal Currents of Air, except along the Line of its Meridian,—is the Country, wherein Columns of cool Air descending on the Water, woud be soon observed.
And they, in Fact, were almost the only People who applied the Observation to common Life: having, according to Herodotus, as well as later Writers, built lofty Structures open at the top. By which Means the cool Air rushing downwards greatly refreshed the Inhabitants.
The ancient Pantheon, at present called All Saints Church, now standing at Rome; built in the lowest Situation of a Street named the Piazza di Navona is on this Construction: and the Hint probably taken from an Egyptian Model.
241. In all inland Countries, whose Lakes are frequently surrounded by Mountains, as Bala-Pool in North-Wales; those of Westmoreland and Cumberland; the Lake of Geneva in Swisserland;—the Air rushes forcibly on the Surface of the Water in descending Torrents: this the Writer has frequently observed.[59]
(In other Languages, the Words applicable to Wind on a Lake, or the Ocean, signify Descent: as, Καταβαινω, and Επικειμαι· also the Northerly or descending Wind corresponded to the Εκνὲφιας while the Southerly or ascending Wind answered to the Απογη.)
All this, which may be allowed to take Place in bad Weather, may perhaps be excepted to, in fine, and still more so, in the finest Weather.
As the slightest Change is first observable on the Surface of Water, whether on Lakes or the Ocean, the Descent of Air in the finest Weather is familiar to Mariners by the Appellation of light airs, playing in Eddies: and particularly in the variable Latitudes; i. e. between 32 and 42: to these the Writer can also witness: as well as on small and large inland Lakes, by partial Dimplings and Rufflings of the Surface.