40 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. y'J 



The similarity of the relations disclosed by examining the various 

 classes of solar heat variation, from those occupying a few days to 

 those occupying many years is striking. That such relations also 

 held through the long cycles of climatic changes disclosed by geology 

 and human history is probable, although concrete evidence is still 

 lacking. The great similarity of the meteorological events which 

 accompanied the glacial and interglacial epochs, to the changes which 

 take place during high and low solar heat variations of comparatively 

 short period, are convincing evidence that solar heat changes played 



Fig. 34. — Correlation between solar radiation and daily maximum temperature. 



an important part in causing those great changes which brought such 

 tragic results to the animal and plant life of the world. The marked 

 fall of temperature in winter which occurs in high latitudes with an 

 increase of only i or 2 per cent in solar heat output, shows that a 

 permanent change of that amount or more would produce a serious 

 change in terrestrial climates, and might pile up permanent ice fields 

 like those of Greenland, in middle latitudes where moisture is 

 abundant, and produce an arid cold in continental interiors where 

 moisture is deficient. 



It is evident from the foregoing investigations that, owing to the 

 large north and south movements of the belts of pressure and tem- 



