34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



either plus or minus, and then suddenly the relationship reversed in 

 sign. Cycles have been found in the weather and have excited hope for 

 a while that a key to weather changes had been discovered, but only 

 to lead to disappointment by disappearing or by changing in phase. 

 Wavelike movements in the atmosphere have been disclosed which 

 continued for a short time and disappeared. A reason for these changes 

 is now offered for the first time in the systematic changes of position 

 in the centers of action in the atmosphere, under the influence of 

 changing solar activity. With the removal of this outstanding diffi- 

 culty, meteorology should show a marked advance, both in theory and 

 in practical weather forecasting, more especially in forecasting for 

 long periods in advance. 



5. The changes in intensity and position of the centers of action in 

 the atmosphere are intimately related to changes in solar activity, more 

 especially to changes in solar heat radiation. The annual means of 

 pressure in these centers of activity, when smoothed, follow in a 

 general way the changes in annual values of sun spots, but there is 

 no relation evident between the two in the changes of short period. 

 Monthly and even shorter periods of change in the intensity of solar 

 radiation show, however, an unmistakable relation to weather changes. 



6. The picture presented in this paper is that of an atmosphere in 

 which the regions of high vapor content in the tropical regions of the 

 earth are strongly affected by changes of solar radiation (presumably 

 by the absorption of the incoming heat rays by the water vapor in 

 the air). The air therein becomes warmer, increases in volume per 

 unit mass, and its pressure falls, attended by an increase in rainfall. 

 Simultaneously, there are centers of action in high latitudes where op- 

 posite relationships are evident. These centers of action all sway back 

 and forth under the influence of changing intensity of solar radiation 

 and changing position of the sun with the season. 



7. When solar radiation increases, the centers of action in high 

 latitudes move farther north and increase in intensity. That is, the 

 pressure over cold regions in these latitudes becomes abnormally high 

 and the temperature falls, while simultaneously the belts of low pres- 

 sure in equatorial regions widen and develop centers of low pressure 

 in middle latitudes. These changes in pressure are attended by winds 

 which markedly influence the temperatures in high latitudes. 



