NO. 7 ASTROPHYSICAL OBSERVATORY, I904-I953 — ABBOT 5 



Mount Wilson, 1905-1920) it was not then possible to be assured of 

 the correlation between solar constant and diametral distribution. But 

 when the family of harmonic variations in the solar constant values 

 became known about 1940, the solar constant value was back-casted 

 from 1920 to 1913, and such correlation seemed indicated. See fig- 

 ures 50 and 51, Pub. 4545.^ Solar contrast observations were dis- 

 continued in 1920, and solar constant determinations have never been 

 made anywhere in the world since 1955. So this correlation cannot 

 now be fully proved. 



PRINCIPAL RESEARCHES 



Leading Operations of the Smithsonian Astrophysical Observatory, 

 1895 to 1955^ (Smithsonian Pub. 4222) gives brief summaries of 

 82 researches, with bibliographic references to the original publica- 

 tions of them. I select here for notice a few of the most important 

 researches which occupied the years 1904 to 1953. 



1. Inventions of pyrheliometers, vacuum bolometer, pyranometer, 



honeycomb pyranometer, two-mirror coelostat, highly sensi- 

 tive radiometer, and solar heat collector. 



2. Absolute measurement in heat units to 1 percent of the solar 



constant, with probable error of a day's measurement at one 

 station ^ of 1 percent relative to other day's measures. 



3. Fixing the limits of sun's radiating temperature as between 



5800° and 7000° C. Abs. Four methods used. 



4. Measurement of atmospheric spectral transmission in 40 wave- 



lengths at 10 stations located between sea level and 14,500 

 feet elevation. 



5. Determining the distribution and intensity of radiation in the 



solar spectrum at 10 stations, and outside the earth's atmos- 

 phere. 



6. Short method for the solar constant, and also automatic balloon 



determination. 



7. Discovery of solar variation between limits of 2.0 percent in 



amplitude. 



8. Discovery of a 27-day period in "solar constant" variation. 



9. Discovery of a numerous harmonic family of exact periods in 



solar variation with a master period of exactly 273 months. 



3 Leading operations of the Smithsonian Astrophysical Observatory, 1895 to 

 1955, by C. G. Abbot. Smithsonian Miscellaneous Collections, vol. 131, No. 1. 

 1955. 



