Pressure and Temperature Results for the Great Plateau. 247 
altogether carry conviction, so far as can be seen at present, to the 
child of science who had seen meteorology at Kimberley. 
It is to be regretted that the very important question of the 
moisture, or humidity, of the atmosphere of the two places does not 
admit of Gomparison, for its importance is not second to that of 
temperature and pressure. In Table 25, however, additional columns 
are inserted giving the amount of cloud month by month at Durban 
and Kimberley from one observation per diem at both places; also 
the moisture at Durban from observation at IX. and XY., and the 
humidity at Kimberley from observations at VIII. The Kimberley 
results for cloud and humidity are extracted from the annual reports 
of the Meteorological Commission, monthly numbers only being 
available: they must be regarded as very rough, although the 
deduced hygrometric state of the air is nearer to the truth than that 
obtained by the Lee wet bulb. The Natal reports give the tem- 
peratures at IX. and XV., and the mean moisture of the same two hours 
expressed in grains per cubic foot ; but the wet bulb, dew-point, and 
humidity are omitted: the want of the first making the exact deter- 
mination of the two latter a task of extreme difficulty and labour— 
almost an impossibility. It will be seen that the greatest cloudiness 
of the sky at Durban occurs during the five months Oct.—Feb., 
jumping at once to its maximum in October, and gradually falling off 
through the season, whereas the moisture of the lower air attains its 
maximum in the four months, Dec.-March. It is during these 
last months, it will be remembered, that N.E. winds prevail over 
Kimberley.* At Kimberley, on the other hand, there is an abortive 
increase in the cloudiness of the sky in October, the maximum not 
definitely establishing itself until the first quarter of the year. Some 
consequences of these changes will be seen when we come to the 
variations in the range of temperature later on. 
The shape of the temperature curves in Fig. 1 obviously suggests 
that their irregularities may be best smoothed out by means of some 
simple sine curves. As a first approximation the equation— 
y=esinatT i 
* See ‘‘ The Winds of Kimberley ” (Z'rans. of the Phil. Soc. of S. Africa, vol. xi. 
pp. 75-112). 
+ ‘‘ Playfair, following the steps of Kirwan, ... endeavoured to create a 
formula which should enable him to approximate to the mean temperature of any 
day: This formula is the following ;— 
y = T+ Fsin (A-30) 
in which T denotes the mean temperature of the given place, F a constant coefficient 
