no. 9 



AREQUIPA PYRHELIOMETRY ABBOT 



19 



We now give in Table 2 mean monthly values of the intensity 

 of solar radiation (e 1 , 2 ) at air mass 1. 2, the transmission coefficient 

 a 2 , the pressure of aqueous vapor p, and the empirical solar constant 

 values e , of which more is said below. The table gives also the 

 number of days on which radiation was observed. This considerably 

 exceeds the number of days on which the atmospheric transmission 

 could be determined. Monthly means based on very meager data 

 are indicated by parentheses. 



Fig. 1. 



General mean: Of £ 1-2 = 1.496; of a 2 = .86o; of p = S-97- 

 Examination of the foregoing table fails to indicate any notable 

 abnormalities covering considerable periods. In other words nothing 

 appears to lead us to suppose that these were not normal years for 

 Arequipa (unless as regards the number of clear days, on which 

 we say nothing) . This is especially interesting, for in the northern 

 hemisphere the year 191 2 was notable for the great decrease in 

 direct solar radiation received at the earth's surface, and of atmos- 

 pheric transparency, which speedily followed the volcanic eruption 

 of Mt. Katmai in June of that year. Remnants of this volcanic 



