APPENDIX 7 



REPOKT ON THE ASTROPHYSICAL OBSERVATORY 



Sir : I have the honor to submit the following report on the activi- 

 ties of the Astrophysical Observatory for the fiscal year ended 

 June 30, 1937: 



WORK AT WASHINGTON 

 REVISION OF SOLAR-CONSTANT VALUES 



At the beginning of the fiscal year preparations were being made 

 to publish a table of best values of the solar constant of radiation 

 since 1930. This table involved the comparison of results from three 

 field stations, searching for errors of reduction, and examining the 

 records of each individual day for evidences of imperfect observation 

 or unfavorable sky conditions. 



But in considering certain discrepancies it suddenly occurred to the 

 Director that a flaw had been overlooked when he devised the so- 

 called short method of reduction in 1923. It will be recalled that in 

 the years 1903 to 1919 all observations of the solar constant had been 

 made by the fundamental or long method. This involved measure- 

 ments of the intensity of sun rays from early morning until mid- 

 forenoon, and about 2 days of computing to yield one value of 

 the solar constant of radiation. Moreover, if the sky gradually be- 

 came cleaier or more hazy during the several hours of observation, 

 the value obtained would be too high or too low, without any means 

 of recognizing this error. 



To save work, to avoid error, and to multiply results, the short 

 method was introduced in 1919. Two solar-constant values could be 

 obtained from observations of only 10 minutes' duration for each, by 

 computations requiring only 1 day for both. In 1923, however, a 

 method occurred to the Director whereby the computing could be 

 almost eliminated, through the use of tables computed once for all. 

 All through the years which have since elapsed this method has been 

 used. Usually, five values were obtained without undue labor for 

 each day observed. 



But some months ago, as above stated, the Director perceived that 

 this brief method has a fatal flaw. Without going into technicalities, 

 the defect consists in this : that if the results of two equally clear days 

 are to be compared, on one of which the sun actually emits 1 percent 



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