294 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. JO 



The barometric fluctuations of the North Atlantic high-pressure 

 region (the Azores) coincide as a rule with similar fluctuations in 

 the South American high-pressure region (probably also in that of 

 the South Pacific and the South Atlantic) and to some extent also 

 with the fluctuations in Siberia. 



It has to be considered that the distribution of pressure, and the 

 situation of maximum and minimum are subject to great alterations 

 summer and winter in Asia as well as in the tropical regions of the 

 Indian Ocean and the Indo-Malayan region; which is not the case 

 in the Atlantic, in the Pacific, and also in the southern Indian Ocean. 

 Hence we cannot expect the twelve-month means of the former 

 regions to give full agreement with those of the latter regions. 



The curves of figures 107 and 108 demonstrate clearly that the 

 pressure changes are much smaller in the tropical regions than in 

 higher latitudes of the northern hemisphere.^ This may to some 

 extent be due to the fact that the tropical low-pressure belt has more 

 regular conditions and a much greater area than the pressure 

 maxima and pressure minima of the northern hemisphere. 



In the high-pressure belt of the southern hemisphere, the baro- 

 metric changes at the South American stations (fig. 107, VI, VII, 

 VIII) are greater than the fluctuations shown by the tropical curves 

 (IV and V), but not as great as the fluctuations shown by the 

 curves III and II for the pressure maximum (Ponta Delgada), and 

 pressure minimum (Stykkisholm) of the North Atlantic. The ex- 

 planation may be, on the one hand, that the high-pressure belt of 

 the southern hemisphere is not as extensive as the low-pressure 

 belt of the tropical regions, but on the other hand, the barometric 

 conditions are more uniform in the southern hemisphere than they 

 are in the northern hemisphere, where there is less ocean. 



According to our earlier investigations we might expect that an 

 increased solar activity would cause an increased circulation of the 

 terrestrial atmosphere, raising the barometric maxima and lowering 

 the minima, at least in some regions. We have found this to be 

 the case for the short periods of some few days, and also for those 

 of about two weeks and of four weeks. We have also found it to 

 hold good for the eleven-year suti spot period, if the fluctuations in 

 the relative number of sun spots or in the daily variations of mag- 

 netic declination may be taken as measures for the fluctuations in 

 solar activitv. 



* It should be noted that the vertical scale (in mm.) for curves I and II is 

 reduced to half the size of the scale of curves III-IX. 



