r8 EGONOEONY OE CaNnTol, On Earth's cold boſfom, as the Sun retires,
-
Confine with folds of air the lingering fires;
ne wiib folds 0f air. 1. 176."Ihe air, like all other bad
condudtors of ele&ricity, 18 known to be a bad condudor of heat; and thence prevents the heat acquired from the ſun's rays by the earth's furface from being(0 ſoon diflipated, in the ſame manner as a blanket, which may be conſidered as a fponge filled with air, prevents the eſcape ot heat from the perſon wrapped in it. Ihis ſeems to be one caufe of the great degree of cold on the tops of mountains, where the SI of the air is greater, and it therefore becomes a better condudor both of heat and elec- tricity. vee note on Barometz, Vol. II. of this work.
"There is however another cauſe to which the great coldneſs of
hi mountains and of the higher regions of the atmoſphere is more (cri< by Dr. Darwin in the
Philoſ. Tranſ. Vol. LXXVIIL who has there proved by ex-
immediately to be aſcribed, explain
+] en zul Inn es zie,.- 1 7. periments with the air-gun and air-pump, that when any por- tion of the atmoſphere becomes mechanically expanded, it ab-
1
ſorbs heat from the bodies in its vici And as the air which
creeps along the plains, ls itſelf by a part of the preſſure being taken off when it aſcends the ſides of mountains; it at the EIG time attraCs heat from the fummits of thoſe mountains, or other bodies AE happen to be immerſed in it, and thus pro-
duces cold. Hence he concludes that the hot air at the bottom of the Andes becomes temperate by its own rarefaßtion when it aſcends to the city of Quito; and by its further rarefadtion be-
mes Cooled to the freezing point when it aſcends to the ſnowy
regions on ths ad of thoſe m ains» Po this alfo he at-
=
O a
:
tributes the great degree of cold experienced by the aeronauts in their balloons; and which produces hail in ſummer at the beight of only two or thiee miles in the atmoſphere.
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