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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



pressure decreases. This fact is also made very apparent by com- 

 paring the individual periods in sun spots with pressure from 1870 

 to 1920. It is also evident that the amplitude Oi of the ii-year period 

 is not dominant as in the sun-spot period ; but as in the case of solar 

 radiation the suljhannonic terms Go, az, and a^, are almost as large as 

 the primary Ci. 



In order to compare the harmonic terms of the ii-|:-year period in 

 pressure in equatorial regions with those in other latitudes, the mean 

 pressure was obtained for each 10° of latitude in the northern hemis- 

 phere for each year from 1890 to 1913. A period of 23 years was 

 taken because from Hale's observations of magnetism in sun spots 

 the complete period of the sun spots is about 22.6, so that 11.3 

 years becomes the second harmonic of this period. From the data 

 thus obtained harmonic terms were computed for each zone of lati- 

 tude and are given in table 9. The phases of the periods varied for 



Table 9. — Amplitudes of the Harmonics of a 22.6-year Period in Pressure 



Note. — In computing the harmonics in Table 9 the means of three or of four periods 

 were used in each case except the case of 02 where two periods were used. The observed 

 values from which oo were computed covered the entire interval of 22.6 years, while the 

 values from which (V72 were computed covered only one twenty-fourth of this interval. 



each latitude as it was evident they must do from the preceding inves- 

 tigation of wave movement. The striking facts brought out are: 

 (i) The amplitudes of the periods increase greatly in high latitudes 

 where they are much greater than in low latitudes and, (2) the 

 amplitudes of the smaller subharmonics in high latitudes are much 

 greater than that of the period of 11.3 years. 



This last finding is of the utmost importance to meteorology, 

 because it shows that the shorter periods are of much more impor- 

 tance in the meteorology of high latitudes than the longer periods of 

 II years or more. These meteorological and solar periods are all 

 believed to be harmonics of longer solar periods. 



Clough found solar periods of 300, 11.3, 7, and 2.5 years, and an 

 analysis of the sun-spot data by Schuster disclosed a number of other 



J 



