168 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



Looking at the weather on a world-wide scale, Clayton has found 

 that pressures oscillate from one region to another in some way which 

 appears to depend upon the intensity of solar activity. He finds 

 there is an opposite trend over the continents and oceans in summer as 

 compared with winter, and that the trend is different in the equatorial 

 regions from that in the extratropical belts. In the equatorial regions 

 temperatures are distinctly lower at sunspot maximum and higher at 

 sunspot minimum. The same is true in the North and South Tem- 

 perate Zones, but in the arid regions bordering the Tropics the 

 temperature actually averages little higher around sunspot maximum 

 than at sunspot minimum. From his studies he concludes that while 

 the North Atlantic shows 10 to 20 percent more precipitation, the 

 eastern half of the United States is in the region where rainfall is 

 actually less during maximum activity on the sun. He concludes that 

 our weather is the result of certain progressive wavelike movements 

 of certain disturbed areas, originating in different parts of the world. 

 With each cycle of change in solar activity, the centers of high baro- 

 metric pressure move from high latitudes to low latitudes and back 

 again. The amplitude of their oscillations and the speed with which 

 these waves progress appears to be inversely proportional to the length 

 of the period of oscillation. 



In years of unusually high sunspot maxima as is the case at the 

 present time, areas of high pressure appear to be pushed farther north- 

 ward. The return of these highs to low latitudes with accompanying 

 colder and clearer weather may, he believes, be so retarded under 

 such instances as to invert the phase of a cycle which has persisted 

 for some time, when the amplitudes of these oscillations have been of 

 less magnitude. Thus there will be several years when the differences 

 in barometric pressure between the equatorial region and North 

 Temperate Zone become greater than normal, and then this period 

 will be followed by several years when the pressure differences become 

 less than normal. The shifting of these centers of action, he believes, 

 is definitely associated with sunspots. 



Mr. Clayton's conclusions are based on so large an amount of data 

 and upon such a wide experience in meteorology that no one interested 

 in weather or weather prediction can overlook the significance of these 

 contributions. One might venture to suggest that one of the most 

 important discoveries in the matter of weather prediction may come 

 as a byproduct of some of these investigations. 



Various attempts have been made to attribute climatic cycles to 

 changes in solar activity. Perhaps the most outstanding scientific 

 contribution in this direction has come from Prof. A. E. Douglass, of 

 the University of Arizona, who has spent a lifetime measuring varia- 

 tions in the tree growth, especially in the forests of the Southwest and 

 in California. Douglass noted that sequences in periods of rapid 



