SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 60 



VARIOUS A. P.O. INSTRUMENTS. 



0.5118 



0.4776 

 0.5072 

 0.5ISO 



0.3760 

 0.3786 

 0.3631 



to. 902 ) 



Jo. 858 !' 

 Jo. 848 



0.3805 

 0.3683 



Mount Wilson, Cal. 



Washington, D. C. 



Mount Wilson, Cal. 



O) U. S. Weather Bureau; (2) Mt. Wilson. 



Washington and Mt. Wilson. 



Do. 

 Washington, Mt. Wilson, Mt. Whitney and Algeria. 



* These values are the factors by which the corrected temperature rise in 100 seconds is to 

 be multiplied to reduce the readings to calories (i5°C.) per square centimeter per minute. 



t These oldest values were obtained from a round-about series of comparisons of several 

 years standing, which now proves to have been erroneous. 



t For 60-second exposures. From Annals Vol. II and later publications. 



Note : On the relation between the Angstrom scale and that of the 

 Smithsonian Institution. — Observations made at the United States 

 Weather Bureau, at Potsdam, and at Pawlowsk have been kindly 

 communicated to the Smithsonian Institution, and we select from 

 them the results of direct comparisons between the best instruments. 

 From these we find the following ratios between readings on the 

 Smithsonian (1913) and Angstrom scales of pyrheliometry : 



Mean 1-039 



