J 6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



It is seen from this map that the latitude effect as pictured in figure 7 

 is increased twice a year when the sun crosses the Equator in March 

 and October. At that time the effect of high solar activity on the 

 pressure is accentuated. The decreased pressure at the Equator, the 

 increased pressure in middle latitudes and the decreased pressure at 

 the poles are greater than at other times of the year. 



Fig. 10. — Excess or defect of pressure at the Equinoxes (March and 

 September) with increased solar activity. 



On the other hand, when the sun is at the solstices in June and 

 December the latitude differences are diminished and eft"ects due to 

 contrasts between land and water are accentuated. The greatest 

 increase of pressure with increased solar activity is over the con- 

 tinents in winter and over the oceans in summer. This is an annual 

 change in contrast to the semi-annual period in latitude effects. The 

 annual effect is shown in figure ii. 



