Climate of South Africa. 251 
showers which the Karroo plains receive are due to such partial 
storms. Shepherds, who depasture their flocks at certain sea- 
sons on those plains, watch for the appearance of lightning, 
and migrate towards the quarter where it has been seen. 
On the other hand, the western districts of the Cape, lying 
between the mountains,and the sea, within the limits to which 
the western monsoon extends northward, enjoy abundant rain 
in the winter months. The north-west wind arrives from the 
sea, surcharged with vapour, and parts with moisture as it 
passes over land cooled in winter below the temperature of 
the sea, and is further sifted of its humidity as it approaches 
mountains still colder. 
Rain descends copiously, but it is only for a short season; 
and frequently too short. Autumnal showers often fail, and the 
harvest of wheat is deficient accordingly. Other sorts of corn, 
sown earlier and reaped sooner, are less apt to disappoint the 
busbandman. 
Concerning the precise quantity of rain which falls in com- 
mon years, and at divers seasons, as ascertained for any oné 
station in South Africa, information is wanting. No observa- 
tions appear to have been yet made to determine this interest- 
ing point of meteorology. Pluviometers, kept at various sta- 
tions, below the mountains and upon them, on the inland side 
of the great chain, and on the sea-side, upon the western coast 
and on the southern, would afford instructive results, con- 
nected with practical questions, no less than with views of 
seience. 
In regard to barometric pressure, this appears from the 
meteorological diaries, to which reference has been made while 
speaking of temperature, to be greatest in winter, and least in 
summer, and the extremes occur in July and January (or Fe- 
bruary), respectively ; that is, in the coldest and hottest seasons. 
The difference between the mean elevation of the mercury in 
the barometer at those seasons, amounts to fifteen hundredths, 
comparing quarter with quarter, and approaches to two-tenths, 
contrasting the coldest with the hottest month. The extreme 
difference between the greatest elevation in winter, and least in 
