Note 67 — Chapter XXXXV
Reading edition
Phil. Trans. for 1777
, Page 470. Thibet in Lat. 31,
cold
with Snow and Frost.
See Ullòa’s Voyage to South-America, Book 6, Chapter 7; where he describes the snowy Mountains, under the Equator.
As the Weather, near the Equinoctial, is more regular, its Changes closely following those of the Moon; and also the Winds and Hurricanes more violent; the Truth of the foregoing Theory will receive the strongest Confirmation by tracing the Effects of depressing torrents of air, in the Island of Jamaica, extracted from the Author already mentioned.
“The cool Vapour rushes from the Mountains towards the hot dry Air, which hovers over the Savannahs or Vallies.
The Rain falls heaviest in the Mountains. Vol. 3, Page 600.
The Land-Wind after Rain, proceeds from that Quarter whence the Rain has fallen heaviest; and seems to rush from above.
In Spain and North-America, the Wind rushes down. Page 601.
When the Land is most heated, the Sea-Breeze blows almost all Night. Page 602.
The Barometer subsides from 1 Inch to 11⁄2 at the full Moon, or just after it.
Wind blows from the Mountains all round the Island: and still a Sea-Breeze over the Mountains: to the Low-Lands, none, 604.
(In Jamaica likewise the Wind blows off the Island every way at once, so that no Ship can any where come in by Night, or go out but early in the Morning, before the Sea-Breeze sets in. See Abr. Phil. Tr. Vol. 3, P. 548.)
Mountain Air rushes down in a continual Current to every Part of the Coast, the Stream descending incessantly throu’ the Night: while heavy cold Air descends to the Mountain Tops, 604.
With a West Wind below there is an East Scud above, 605.
Mountains cloudy, low Lands sunny. 606.
In all the River-Courses of Jamaica, there is a sensible Current of Air. Rain never comes without some Wind: and the Showers almost invariably follow the very Meanders of the larger Rivers, 608.
Rain always cools: the Thermometer falling, after a Shower, from 6 to 8 Degrees, 610.
(And Iron rusts least in rainy Weather: [the Air being then driest,] descending from the upper Regions. Abr. Ph. Tr. V. 3, P. 546.)”
It is said also that “in Jamaica the Clouds gather, and shape according to the Mountains: so that old Seamen will tell you each Island towards Evening, by the Shape of the Cloud over it.”
The Sea-Breeze, being counterpoised by Descent of the etherial Air, produces a calm.
The same Author likewise says, that “the Clouds begin to gather about 2 or 3 o’Clock in the Afternoon at the Mountains, and do not embody first in the Air, and after settle there, but settle first and embody there: the rest of the Sky being clear till Sun-set. So that they do not pass near the Earth in a Body, and only stop where they meet with Parts of the Earth elevated above the rest; but precipitate from a very great Height, and in Particles of an exceeding rarified Nature; so as not to obscure the Air or Sky at all: that great Variety of beautiful Colours in the Canopy of Heaven being raised to a much greater Distance [he means Height] in Jamaica than it is here.” Abr. Ph. Tr. V. 3, P. 557.
(Prognostics of Weather, at certain Periods of the Moon, are mentioned by Captain Langford. Lowthorp’s Abr. Phil. Trans. Vol. 2, Page 105.)