NO. 7 



THE ATMOSPHERE AND THE SUN CLAYTON 



43 



of pressure, when it rises in one part of the world, there is an equiva- 

 lent fall in other parts. These centers of rise and fall are not fixed 

 in position, but shift their position tO' some extent as illustrated in 

 the case of a 25-month period in a preceding paper of this series.' 



The variations in intensity and phase of solar and meteorological 

 cycles makes the investigations of the separate cycles difficult. The 

 use of the Fourier series and of the Schuster periodogram are not 

 well adapted to such work. In order to meet these difficulties I 

 devised the correlation periodogram ' which is to a considerable 

 extent independent of variations in intensity of the periods ; but 

 does not overcome the difficulty of shifting of phase. The best 



Fig. 30. — 72-year sun-spot cycle. Means of 3 cycles, showing apparent inversion. 



method appears to be to use trial periods of successively greater and 

 greater length and harmonic analysis for each individual oscilla- 

 tion ^ ; then to combine the results for each period into groups of 

 3, 5, 10 or more. By this method the curve in figure 28 was 

 obtained. This method of research, using groups of 10, has made it 

 f>ossible to analyze and to follow the changes of a great number of 

 meteorological periods and to recombine them by synthesis for a 

 trial in practical forecasting. Such analyses of more than 100 cycles 

 have convinced me that these cycles follow solar cycles of the same 

 length and that they are, mostly at least, harmonics of long solar 

 cycles. 



^ Smithsonian Misc. Coll., Vol. 78, No. 4, p. 48, 1926. 



^ Smithsonian Misc. Coll., Vol. 71, No. 3, p. 15, 1920. 



'Clayton, H. H., World Weather, p. 376, New York, Macniillan & Co., 1923. 



