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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



or a complete reversal in phase. Figure 29 shows what appears to be 

 a reversal in phase in the sun-spot cycle. The average length of this 

 cycle is about 11 years, so that two cycles occur in 22.5 years. If the 

 cycles are plotted in 22-year periods as in figure 29 it is seen that in 

 the period 1770 to 1792 the cycle is nearly inverted in phase to the 

 cycles occurring 22 years earlier and 22 years later. It is, however, 

 quite possible that this result is due either to interference of periods 

 of different lengths, or tO' lack of accuracy in the early observations. 

 No such apparent inversion has occurred since 1800. 



Fig. 29. — ii-year sun-spot cycle, showing apparent inversion of phase. 



In figure 30 is given what appears to be a reversal of phase in the 

 7^-year period. This cycle was in one phase from 1848 to 1870, 

 as shown by the broken curve in figure 30, but appears to have been 

 in an opposite phase from 1825 to 1847, as will be seen by the con- 

 tinuous curve in figure 30. This type of change is found in every solar 

 and meteorological period. Brooks and Clough seem to think that 

 shif tings of phase are gradual ; but my own researches lead me to 

 the opinion of Professor H. H. Turner that the changes are sudden 

 and of the nature of discontinuities. 



The change of phase in meteorological cycles is not brought about 

 entirely by changes in phase of solar cycles; but is in part, at least, 

 due to shifting of centers of action in the atmosphere. In the case 



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