l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



CONCLUSION 



I feel that I may now justly claim to have made with my associates 

 three discoveries of merit: 



1. The sun's radiation varies far beyond accidental errors of 

 observation, in numerous harmonic periods exactly related to 273 

 months. 



2. Harmonic periods of these identical lengths exist, and with 

 much greater percentage amplitude, in long records of the precipita- 

 tion at scores of stations in all parts of the world. 



3. Useful forecasts for many future years may be made when 

 amplitudes and forms of these harmonic periods are determined from 

 official records of precipitation for many past years. 



It is shown that such forecasts are as close to observation at inter- 

 vals when wide departures from the normal occur, as when the 

 precipitation is nearly normal. (See Smithsonian Publication 4471, 

 page 6, 1961.) 



It would be interesting if some expert in mathematics should dis- 

 cover why terrestrial precipitation reacts so strongly to small per- 

 centage changes in the solar constant. I suggest a possible explana- 

 tion in Smithsonian Publication 4135, page 3. 



Mathematics may even be necessary in order to trace effects of cer- 

 tain human actions which may make records of the past inaccurate for 

 future forecasts. Such may be super-powerful nuclear bombs, com- 

 bustion of long train-loads of oil to propel spacecraft, and means 

 used to effect changes in weather to improve it, as now proposed. All 

 these may change atmospheric circulation and make past records use- 

 less for forecasting in the future. 



LITERATURE CITED 



Solar variation, a leading weather element, by C. G. Abbot. Smithsonian 

 Miscellaneous Collections, vol. 122, No. 4. 1953. (Smithsonian Publica- 

 tion 4135.) 



A long-range forecast of United States precipitation, by C. G. Abbot. Smith- 

 sonian Miscellaneous Collections, vol. 139, No. 9. 1960. (Smithsonian 

 Publication 4390.) 



A long-range temperature forecast, by C. G. Abbot. Smithsonian Miscellaneous 

 Collections, vol. 143, No. 5. 1961. (Smithsonian Publication 4471.) 



Solar variation and weather, by C. G. Abbot. Smithsonian Miscellaneous Col- 

 lections, vol. 146, No. 3, 1963. (Smithsonian Publication 4545.) 



