32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



Similar charts for other intensities show that in general the northern 

 centers of action are farther north with increased intensity of solar 

 action and farther south with decreased intensity at all seasons. These 

 charts show, as did the preceding charts, that with increase of solar 

 radiation the pressure falls in those regions where the vapor pressure 

 and the temperature are abnormally high for the latitudes in which 

 they are found, whereas increases of pressure are found where the 

 vapor pressure and temperature are l^elow the normals for the latitude. 



PROGRESSIVELY MOVING WEATHER WAVES 



Numerous examples have been given in preceding papers of this 

 series and in other publications of the progressive wavelike move- 

 ments of weather areas in different parts of the world. These pro- 

 gressive movements can probably be explained in large part, at least, 

 as due to the movements of the centers of action in the atmosphere 

 with varying intensity of solar radiation. During each cycle of change 

 in solar radiation the centers of excess pressure move from high lati- 

 tudes to low latitudes and back again. These changes in position can 

 be interpreted as waves that progress with a velocity inversely pro- 

 portional to the length of the period of oscillation. In the shorter 

 waves the west to east drift of the atmosphere in middle latitudes also 

 plays an important part in the progressive motion. 



SUMMARY 



I. There is something in common in the weather in widely separated 

 parts of the earth, even in countries on op^Dosite sides of the earth, 

 as for example the central United States and Australia. Changes 

 in rainfall in central North America .show a similarity to changes 

 in central South America. Changes in pressure in the Indian Ocean 

 show similarities to changes of temperature on the coast of Chile. 

 Annual pressure means in San Diego vary in the same way as in 

 Buenos Aires, and pressures in Ceylon vary inversely to those in 

 Santiago, Chile. Many such relationships have been shown by other 

 investigators. 



It is suggested that these common features are brought about by 

 changes in the intensity of the circulation of the earth's atmosphere. 

 In confirmation of this view it is shown that there are periods lasting 

 for several years when the pressure gradient between the equatorial 

 region and the colder regions in high latitudes become greater than 

 normal, and succeeding years when it becomes less than normal. This 

 simultaneous change in the pressure gradient north and south of the 



