244 Mr. Colebrooke on the 
the plain is mitigated by a cool wind descending from the 
mountain’s side, and the coldness of the blast is tempered by 
the reflected heat of the earth’s surface. Hence a moderate 
temperature, where the wind has free passage, is the result, 
even in summer, at the Cape. The prevalence of clear sun- 
shine, with the consequent heat of the ground, is at the same 
time sufficient for ripening the productions of warm climates ; 
while the winter, which is likewise moderate, is, in a similar 
degree, suited to the summer produce of cooler regions. 
Concerning the hygrometric condition of the atmosphere, I 
have to adduce none but desultory observations made by my- 
self, during a few months. They were summer months; and 
the observations have supplied some facts, which I have used, 
and shall further employ, in course of touching upon topics 
on which they bear. 
I use, by way of hygrometer, a common thermometer, of 
which the scale is detached from the bulb. Upon wetting the 
bulb with water, and exposing it wet to the air, the consequent 
evaporation of moisture from its surface lowers the temperature 
more or less, according to the dryness of the air. 
For a common measure to serve for comparison, the degrees 
of dryness are reduced to the centesimals of the air’s capacity 
for moisture, at the observed temperature. 
The following is a summary of observations with this very 
simple instrument, during summer months (December to March), 
at Cape-Town, near Table-Bay; and at Hottentots’ Holland, 
near False-Bay. 
Dryness, in the morning before sunrise, is ordinarily from 
6° to 7°, the utmost 12°, the least 3°; which, fora mean tem- 
perature of 77°, answer to about .17 to .20 centesimals .30, 
and .09, respectively. The atmospheric dryness usually aug- 
ments as the day advances; for, while the temperature rises 
towards noon, the point at which the hygrometric thermometer 
becomes stationary, remains more nearly uniform. The maxi- 
mum at noon was 26°, (viz., 92° — 66°). The utmost range of 
difference of dryness within the day amounted to 35°, viz., hy- 
