64 CLIMATIC CYCLES AND TREE GROWTH 



This application of our analytical method makes use of tree-ring and meteoro- 

 logical records. The second application will be in examination of the rela- 

 tion between climatic or other terrestrial changes and changes in the sun. A 

 third, equally important application, is the recurrence of discontinuous 

 periods during long time intervals of the earth's history. This makes use of 

 very long records in tree rings and varves. 



The fourth and perhaps most general application of the discontinuous 

 period is its quantity production from wide but homogeneous sources and its 

 grouping into frequency periodograms. Such periodograms can equally 

 well be secured from dated or undated material provided the counting is 

 accurate and therefore they can bring together evidence from modern trees, 

 fossil trees, varves, and other sediments. It offers an exceedingly wide 

 opportunity for stating certain general facts about climatic variations. 



The fifth and last application of the discontinuous period in this brief list 

 is in climatic prediction problems. Whether climatic cycles are permanent 

 or not, whether they come from the sun or not, they become applicable to 

 climatic forecasting in their function as natural units of greater length than 

 the year. On the basis of the difference between the year and these longer 

 natural units we can improve our probabilities of successful prediction and 

 lessen our errors without settling beforehand the complete physical source 

 of these variations. The fact that now and then one of a group changes or 

 even disappears does not overcome the value of using the cycle complex that 

 is actually in operation. As we find more and more their physical source 

 and the rules of their behavior, the value of prediction will increase toward 

 the desired accuracy. If these longer natural units admittedly emanate 

 from the sun, then observations of the sun containing valuable advance in- 

 formation will become of great importance. 



