12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



low solar activity. The opposite conditions are here found ; the pres- 

 sure is higher in the tropics and near the pole, and lower in middle 

 latitudes than the normal pressure. 



Another fact to be noted is that the maximum of pressure between 

 30° and 40° latitude and the minimum of pressure between 60° and 

 70° latitude are nearer the pole when solar activity is high than when 

 solar activity is low. This same condition prevails in both the north- 

 ern and southern hemispheres. 



The changes of pressure due to a change from low to high solar 

 activity are shown in figure 7. where the changes for each 20° of 

 longitude and 10° of latitude are plotted on a chart of the northern 

 hemisphere with a polar projection. This map shows a decreased pres- 

 sure all around the world in latitudes of 0° to 30° with increased solar 

 activity. It shows increased pressure between latitudes 40° to 60° 

 and diminished pressure in the polar basin. But there is evidently 

 a longitude efifect also. The excess of pressure in latitudes 40" to 

 70° is greatest over the Eurasian continent and least over the Pacific 

 Ocean. 



If the values in tables 3 and 4 are corrected for latitude efifect by 

 subtracting the mean values in the last column of the tables, there 

 is seen to be a distinct tendency for the pressure in all latitudes to 

 be low over the Pacific and high over Eurasia, witl» increased solar 

 activity. Subtracting the yearly means in table 4 from those in table 3 

 and correcting for the latitude effect, the data were obtained from 

 which figure 8 was drawn. The tabulated results are shown in 

 table 5. 



Table 5. — Longitude Differences. Differences in Millibars betiveen the Yearly 

 Means in Tables .? and 4 Corrected for Latitude 



Figure 8 brings out clearly an excess of pressure over the Eura- 

 sian continent with increased solar activity, the maximum being in 

 latitude 50° to 80° N.; while a defect is evident over the Pacific 

 Ocean and North America, the greatest depression being in high lati- 



