REPORT OF THE SECRETARY. 



65 



Computations from the Mount Whitney results confirm Yntema's conclusion 

 that the great increase of brightness toward the horizon can not be clue to any 

 arrangement of starlight, but must be caused by some terrestrial source of 

 light, perhaps a continuous faint aurora. 



Bolometric measurements were made on Mount Whituey to determine the 

 relative radiation of the sky by day in all directions, as compared with the 



sun. These measurements were numerous aud seem to have been successful. 

 but are not yet reduced. 



The sun's energy spectrum.— A summary has been prepared showing the mean 

 result of determinations of the distribution of the sun's energy in the spectrum. 

 as.it would be found outside the atmosphere. The measurements on which it 

 is based include Washington, Mount Wilson, aud Mount Whitney work of 1903 



