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 11%-Year 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 dififerent. The amplitude of the 

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

 decidedly predominant while in the solar radiations the amplitudes 

 of the harmonics of ^, ^, and \ of 1 1.3 years, a-., a-^, and a^ are almost 

 as large as the primary a^. 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\ 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 ii-year periods, 

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



Table 8. — Harmonic Terms for iiy^-Year Period in Pressure, 1890-1913 



Mean Pressure of 9 Equatorial Stations 



Epoch 1895.0=1917.5 



Ai = 325° ai = o.36mb. 



A2 = 29° 02 = 0.32 mb. 



A3 = 265° Oi = 0.25 mb. 



A4=i5o° 04 = 0.35 mb. 



This comparison indicates that in the ii^j-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 



