io TRAVELS IN 
funnel of a pair of bellows, or under a water-spout. On the 
Cape side of the mountains tlie thermometer rarely descends 
below 40°; but on the elevated Karroo plains, within the 
mountains, it is generally, in the winter months, below the 
freezing point by night, and from 70 to 80 in the middle of 
the da}''. 
I think this intense cold of the Karroo plains, beyond what 
might be expected from their parallel of latitude or elevation, 
may satisfactorily be accounted for from the ingenious experi- 
ments of Mr. Von Humboldt, on the chemical decomposition 
of the atmospherical air. He proves that fat and ciayej'^ earths 
are strongly disposed to attract the oxj'^gen from the atmo- 
sphere, by which the azotic gas is let loose; and this gas, en- 
tering again into combination with the fresh oxygen of the 
superincumbent stratum, in an increased proportion, forms 
nitric acid, from which saltpetre is^enerated. That saltpetre 
is abundantly formed on those plains is an indisputable fact, 
as I have fully shewn in the first chapter of the first volume; 
and the consequence of such formation must necessarily be a 
great diminution of temperature in those places whej-e the 
operation is most powerfully carrying on. Hence perhaps 
may be explained those columns of cold air through which 
one frequently passes upon the Karroo plains. 
The north-west winds of winter have a moist and cold feel 
even in Cape Town, where, though the thermometer seldom de- 
scends below 40°, and then only about an hour before sun- 
Ti>se, all the English inhabitants were glad to keep constant 
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