SOUTHERN AFRICA, 33^ 
ward fide of the Table Mountain, and the former to leeward of 
it ; from whence, alfo, the rays of the meridian fun are thrown 
back upon the town, as from the furface of a concave mirror. 
The variation of climate, to which the Table Valley is fubjedt, 
led one of the Britifh officers to obferve that thofe who lived in it 
were either in an oven, or at the funnel of a pair of bellows, 
or under a water-fpout. On the Cape fide of the mountains the 
thermometer rarely defcends 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 day. 
I think this intenfe cold of the Karroo plains, beyond what 
might be expeded from their parallel of latitude or elevation, 
may fatisfadorlly be accounted for from the ingenious experi- 
ments of Mr. Von Humboldt, on the chemical decompofition of 
the atmofpherical air. He proves that fat and clayey earths are 
ftrongly difpofed to attract the oxygen from the atmofphere, 
by which the azotic gas is let loofe ; and this gas, entering again 
into combination with frefh oxygen, of the fuperincumbent 
ftratum, in an increafed proportion, forms nitric acid, from which 
faltpetre is generated. That faltpetre is abundantly formed on 
thofe plains is an indifputable fad, as I have fully ftiewn in the 
fecond chapter of the firfi: volume ; and the confequence of fuch 
formation muft neceffarily be a great diminution of temperature 
in thofe places where the operation is moft powerfully carrying 
on. Hence may be explained thofe columns of cold air through 
which one frequently palfes upon the Karroo plains. 
u u 2 ■ , The 
