NO. 5 



SOLAR VARIABILITY ABBOT, FOWLE, ALDRICH 



Table 4. — Auxiliary standard reduction values of 1913 



Table 5. — Standard distribution of radiation along radius of solar disk, 1913 



CHANGES OF DISTRIBUTION FROM YEAR TO YEAR 



We have compared the distribution for 1907 with that for 1913. 

 It was at once apparent that a change of distribution had occurred. 

 Inasmuch as the year 1913 was a year of absolute minimum of sun 

 :spots such as has not been equaled for almost a century, it seemed 

 well to use the distribution obtained in 191 3 as a standard of refer- 

 ence. 



Imagine tables to be formed for other years, similar to that which 

 -we have just given for 1913. Imagine, further, that we divide each 

 number of the table for another year by the corresponding number 

 of the table for 191 3. There results, for each wave length, a series 

 of values. Having adjusted the values so that smooth curves to 

 represent them would give zero departures at the center of the sun's 

 disk, the actual values, starting near unity at the center of the 

 sun's disk, run to numbers slightly smaller or larger than unity as we 

 approach the edge of the disk, according as the distribution in the 

 given year shows a greater or a less contrast of brightness between 

 the center and the edge than that which prevailed in the standard 

 year 1913. 



In the following table (6) are given the results of such comparisons 

 ior the years 1907 and 1914. It was necessary to reduce the observa- 



