NO. 8 HARMONIC PERIODS IN PRECIPITATION — 'ABBOT 1 3 



both curves show four major episodes. They are 1922 to 1928; 1928 

 to 1940; 1940 to 1949; and 1949 to 1954. Curve (C) is rigidly con- 

 ditioned by observation. But curve (D), on the other hand, depends 

 on forecasting, based on all the monthly observations, 1884 through 

 1956. 



It shows in D, however, the same four great trends in precipitation 



Table 3. — Harmonic Periods in Solar Constant Exact Fractions of 

 273 Months, Category 2 Only 



as those actually observed to be real in (C). If the forecasts making 

 up curve (D) were not sound, there is not one chance in a thousand 

 that the two curves would be so similar. Moreover, the curve (D) 

 has a smaller average departure from curve (B) than curve (C) has 

 from curve (A), and curve (D) is far smoother than curve (C). 



Now we turn to Nashville in figure 8, with its four curves of the 

 same letters as Rochester. Obviously the same remarks hold almost 

 in toto. 



