NO. 7 THE ATMOSPHERE AND THE SUN CLAYTON 33 



dominating period in weather changes. Such a relation has not been 

 found and the reason appears to be that weather changes follow 

 changes in solar radiation more closely than they do sun-spot num- 

 bers, and solar radiation is more variable and shows a more complex 

 periodicity than do sun spots. 



When the ii-year period 1917 to 1928 is analysed harmonically 

 for sun spots and solar radiation, the results in table 7 are obtained. 



Table 7. — Harmonic Terms for ii^-Vear Period in Sun Spots and Solar 



Radiation 



These results show that in a general way the oscillation in the num- 

 ber of sun spots and in the intensity of solar radiation are in the 

 same phase — that is, when one increases the other increases ; but the 

 amplitudes of the changes are very different. The amplitude of the 

 primary oscillation, Oj, in the sun spots (the ii:^-year period) is 

 decidedly predominant while in the solar radiations the amplitudes 

 of the harmonics of ^, j, and ^ of 11.3 years, a^, a^, and a^ are almost 

 as large as the primary Oi. The pressure data for tropical stations for 

 the II years 1917 to 1928 are not available at present, so that a com- 

 putation of pressure changes was made by going back two periods of 

 II J years to January, 1890, and computing the harmonic terms from 

 the mean pressure of nine equatorial stations extending from Quix- 

 eramobim in Brazil eastward across Africa and the Indian Ocean to 

 Maiden Island in the Pacific. The data covered two 11 -year periods, 

 1890-1913, and the epochs were taken at 1895.0=1917.5. 



Table 8. — Harmonic Terms for 11%-Vear Period in Pressure, iSgo-igis 



Mean Pressure of 9 Equatorial Stations 



Epoch 1895.0 = 1917.5 



Ai = 325° Oi = o.36mb. 



A2 = 29° 02 = 0.32 mb. 



As = 265° Oa =^ 0.25 mb. 



A4=:i5o° 04 = 0.35 mb. 



This comparison indicates that in the ii^^-year period in pres- 

 sure in the Tropics, the phase is in general terms opposite to that 

 of sun spots and solar radiation, and hence when these increase the 



