14 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



Figure 12 shows the annual means of sun spots and solar radiation 

 during two sun-spot periods. The continuous curve is plotted from 

 the relative sun-spot numbers and the dotted curve from the mean 

 values of solar radiation. During the period 1912-23 the long period 

 oscillation of radiation is the same as that of the sun spots, but 

 during the period 1923-33 this relation is not apparent. 



At times the month to month variations of solar radiation and of 

 atmospheric pressure are strikingly similar. In figure 13 the continu- 

 ous curves are plotted from the departures from the lo-year averages 

 of the monthlv means of solar radiation observed in the same month 



Stmspota 



Solar radiation 



1923 19E7 1931 1934 



-calories 



Fig. 12. — Sun spots and solar radiation annual means. 



of succeeding years. The broken curves are plotted in the same way 

 from monthly departures of atmospheric pressure in the centers of 

 action in the atmosphere. The values of solar radiation are taken 

 from table 45 of the Annals of the Astrophysical Observatory of 

 the Smithsonian Institution, vol. V, p. 278, and the pressures are taken 

 from World Weather Records, 1921-1930, Smithsonian Miscellaneous 

 Collections, vol. 90. 



It is seen in figure 13 that in the high-pressure center ofT the coast 

 of Lower California in winter the solar radiation during the decade 

 192 1 -1930 varied in a; general way in the same sense as the pressure, 

 whereas in the Tropics during the interval from April to September 

 it varied in an opposite way — that is, the pressure fell when the solar 



