The Barometer in South Africa. 



75 



zone is about io° N. Lat. We might expect that the single annual 

 component would be replaced by a double variation due to the double 

 passage of the Sun through the zenith, — this is not so, however, the 

 double term becomes greater, but it is not larger than the first term 

 except in Senegal. 



The amplitude of the first term, so far as it is due to Sun-power 

 should vary as some function of the height of the barometer and the 

 difference between the highest and lowest temperatures, but in 

 addition to these two factors, there is a third depending on the amount 

 of aqueous vapour present. The temperature difference is greatest 

 over continental areas whilst the amount of aqueous vapour has the 

 most influence at marine stations. 



The accompanying maps show the amplitude and phase of the 

 first term over South Africa. 



Mr. V. A. Lowinger has assisted me in the compilation and 

 computations of this section. 



Fig. 2.— Amplitude of First Term. 



