NO. 5 



SOLAR VARIABILITY ABBOT, FOWLE, ALDRICH 



if the solar radiation fluctuates from year to year. Greater values 

 of solar radiation prevailed in 1907 ' and 1914 than those prevailing 

 in 1913. Hence it is not surprising to find that the contrast of 

 brightness was greater in both the years 1907 and 1914 than it was 



0.0 02 0.4 0.6 0.8 .1.0 ao 0-2 0.4 oe aa i 



X 



Fig. 4. — Variability of distribution of sun's brightness from year to year 



in the year 191 3. Third, there seems to be a correlation of change 

 of contrast with change of wave length. This relation does not 

 appear clearly from the results of 1907, but figure 4 shows that these 

 results are subject to large experimental error compared with the 



^ This statement regarding 1907 is based on the dependence between solar- 

 constant values and sun-spot numbers indicated by figure 16 of Vol. 3 of our 

 Annals. Few solar-constant determinations were made in 1907. 



