Meteorological Features. 129 



The fluctuation of the barometer is very small at Bulawayo (Lat. 

 20° 9'). The mean of the extreme ranges for eight years gives only 

 .222 of an inch. The difference between two consecutive days in the 

 two years under consideration was nearly always under .1, the highest 

 was .158. 



The correspondence in even this summary handling of the figures, 

 between barometer and wind changes, points out the importance of 

 relatively small pressure variations in these latitudes. 



The air temperature results show on the whole the truth of the 

 statement that a low temperature corresponds to East winds ; there 

 are more inversions, however, than in the pressure figures, but the 

 Black Bulb tem.peratures show a remarkable correlation. Out of 70 

 periods of daily veering winds which occurred from April, 1904, to 

 November 9th, 1905, during which time the Black Bulb readings 

 were taken, 54 show a higher temperature than in the East Winds that 

 preceded or followed. The differences are sometimes very large, 

 especially in the rainy season. Clouds covering the sky in the middle 

 of the day may partly account for this great difference, but in the 

 rainy months clouds appear after 10 a.m. nearly every day, so that 

 the chances may be said to be equally distributed. But the same 

 sequence of high and low temperatures, though with smaller 

 differences, is observed in the clearer months, for instance in July and 

 August, when the cloudiness comes down to i.i. 



The variations of the Relative Humidity are also very interesting. 

 Even in the rainy season, with a large amount of rain in the low 

 barometer periods, there is a marked lower Relative Humidity than on 

 high barometer and East wind periods. The temperature variations 

 partly account for that, but not completely, I think. The East Wind 

 must be more saturated with moisture, although a large amount of it 

 has often been deposited on the high lands of the Eastern coast. To 

 settle this point satisfactorily, the dew point and absolute humiditv 

 figures would be required. It might be said also that the greater 

 relative humidity corresponding then to the East winds may be 

 considered as the effect of the rains that fell in the preceding days, 

 especially as the rains setting in from some other direction with 

 thunderstorms, often continue as slow rains with winds ranging from 

 E. to S. But the same sequence of high relative humidities with 

 easterly winds and low ones with other winds is prevailing with much 

 more marked differences in the dry season when no rain falls. The 

 Relative Humidity curves show a peculiarity worth mentioning. 

 During East Winds the amplitude is very great, ranging often from 

 10 per cent, or lower to 90 per cent, or over, whilst during the other 

 periods the dailv curve is verv contracted round the mean of the day, 

 the maximum remaining considerably lower than the maximum during 

 the East Winds. 



Special mention ought to be made of the periods in which the 

 wind passes from E.S.E. or E. to N.E. or N. in the middle of the 

 day and back, usually some time in the afternoon before sunset. This 

 might correspond to the law which Dr. Sprung* gives in his 



* Lehrbuch der Meteorologie. 1885 p. 345. 



