554 E. HUNTINGTOX SOLAK HYPOTHESIS OF CLIMATIC CHANGES 



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Then in succeeding cycles the maxima 

 become mo&'e and more pfronounced 

 until, in 1778, the number was 154.4, 

 or nearly twice as much as in 1750. 

 Thereafter there is a decline to only 

 45.8 in 1816. An increase again fol- 

 lows, and from 1837 to 1870 we have 

 four maxima, all of which are above 

 95. Then the number of spots falls off 

 once more. If we look at the dotted 

 line joining the minima we see that it 

 rises and falls in the same way as the 

 line joining the maxima, although not 

 nearly as much. In 1810 there were 

 no sun-sj)ots. An equally inactive state 

 of the sun was not again attained until 

 1913. The low state of both the max- 

 ima and minima at these two dates in- 

 dicates a cycle whose length is some- 

 where near a century. The interval 

 from one main maximum to the next 

 happens in this case to be somewhat 

 different from the interval between the 

 chief minima. The first great maxi- 

 mum comes in 1778. Then comes an- 

 other period of maxima with two main 

 crests, one in 1837 and one in 1870. 

 In figure 18 two heavy lines have been 

 drawn at a height of 95 in order to 

 bring out the periods of many sun-spots 

 as compared with the periods of few. 

 It is remarkable that not only does the 

 height of the maxima vary at different 

 periods, but the length of the individual 

 cycles varies in the same way. Appar- 

 ently at the end of a period of abundant 

 solar activity the active force, whatever 

 it may have been, becomes dormant 

 and we have a long interval before an- 

 other and much smaller maximum ap- 

 pears. For instance, the interval from 



