74 



CLIMATIC CYCLES AND TREE GROWTH 



Abbot, who is unquestionably the highest authority on solar radiation, 

 has made cycle analysis of his monthly values using an instrument of his 

 own invention, the periodometer. This instrument is especially good at 

 cycle summation and subtraction. His cycle lengths are first estimated by 

 eye from the original curve. 1 By this form of integration he can test esti- 



Weak cycle Good cycle 



Norma I cycle — Very good cycle — 



6 7 8 9 10 II 12 13 14- 15 16 17 18 19 20 21 22 



1750 

 1760 

 1770 

 1780 

 1790 

 1800 

 1810 

 1820 

 1830 

 1840 

 1850 

 I860 

 1870 

 1880 

 1890 

 1900 

 1910 

 1920 

 1930 



5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 21 22 



Months 

 d 

 Fig. 31 — d. Chrono-periodogram of same. 



1 The periodometer has the data set up on a right-hand drum and integrates it by 

 a system of fractioned additions {i.e. it finds the sum of each occurrence divided by 

 number of occurrences). This produces on left drum a continuous repetition of equal 

 integrations. Then the integrated values on left drum are caused to subtract them- 

 selves from the originals on the right drum. Smoothing may be performed also. (See 

 Bibliography, 1932 3 and 1935.) 



