The Barometer in South Africa. 



77 



Fisc. 5. — Phase of Second Term. 



Movement of Atmospheric Disturbances across South 

 Africa. 



The annual variation of tlie barometer and the mean distribution 

 of pres.sure from montli to month control the more constant climatic 

 features. A low mean barometer does not necessarily mean rain. It 

 is true the season of the mean low barometer over the greater part of 

 South Africa coincides with the Summer wet season, but this is not 

 so over the region of the Cape Peninsula, — if so, the Summer with its 

 low barometer should be wet and Winter with its high barometer 

 dry, whereas, as a matter of fact, the Peninsula Summer is dry, the 

 Winter wet. Rainfall is not associated with a mean low barometer 

 but generally wdth a barometer below the mean of the season, fine 

 weather with a barometer above the mean of the season. The steady 

 maich of the barometer is continually disturbed by the passage of 

 depressions which bring disturbed weather. If we can find out the 

 presence of a depression and in what direction it is moving, it becomes 

 possible to predict the weather in its neighbourhood and path. If, 

 on the contrary, there are no indications of anv depression, it is safe 

 to predict fine weather. Depressions usuallv travel from W to E* and 

 generally move away from the equator. If a depression is travelling 



