ANALYSIS OF TERRESTRIAL RECORDS 



103 



In these 130 curves, covering the age of the sequoias, a recurrence cycle 

 of about 270 years seems to be a common character, as shown in this prelimi- 

 nary study. A cycle about 100 years long is common to them all and some- 

 thing near 220 years is seen occasionally. Ordinary cycles of all these values 

 are mentioned by Turner. Something near 300 years is discussed by Clough. 

 Dr. Alter mentions 250 years for possible recurrence. The double value near 

 560 years probably exists in our data, and it is possible that it will prove im- 

 portant. In order to visualize the possibilities, a 275-year length is taken 

 as a workable solution for the time being. A provisional pattern based on 

 this 275-year recurrence is shown in figure 45. This diagram shows the 

 sequence of different short cycles in the 275-year pattern derived from 2000 



Fig. 45 — Average cycle recurrence in Grant Park sequoias in 2100 years. 



years of the Grant Park sequoias and is a very promising sign at the present 

 time. In it we find that the persistence of the Hellmann cycle since 1750 

 agrees with previous recurrences of that cycle. If the various cycles con- 

 tinue as they have done, we have some reason to expect that through the 

 next 70 years this Hellmann relation should be less conspicuous or absent, 

 with a probability of replacement by a 23-year cycle or the same divided 

 into five equal parts. 



This pattern therefore encourages us to hope that from the giant sequoias, 

 checked by historical material, we shall obtain in some form of cycle sequence 

 a real step forward toward a theory of climatic change and long-range pre- 

 diction. This is the thought that inspires our attack upon the cycles in 

 the long chronologies. 



