SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 66 



by removing the glass screen K it may be used for nocturnal radiation. 

 We have not as yet employed the instrument much for the measure- 

 ment of nocturnal radiation nor have we as yet compared its readings 

 under that arrangement with the radiation of enclosures at different 

 temperatures. We hope to make such experiments in future. We 

 have made numerous comparisons between the instrument as arranged 

 for day observations and the pyrheliometer. A series of observations 

 of this kind, interspersed by readings on the whole sky, is shown in 

 table I. A close agreement with the results of Pvrheliometer A. P. 



Table I. — Summary of Results of March 31, igi6 

 North Tower, Smithsonian Institution 



Sec. Z 



Pyranometer A. P. O. No. 6 



Sky alone 

 Glass on 

 (Calories) 



Sun and 



sky 



Glass on 



(Calories) 



Sun alone Sun alone* 

 Glass on No glass on 

 (Calories) j (Calories) 

 (x Sec. Z) I (x Sec. z'l 



Pyrheli- 

 ometer 

 A. P. O. 



No. 9 

 (Calories) 



Pyrheli- 

 ometer 

 A. P. O. 



No. 9. 



Pyranome- 

 ter A. P.O. 



No. 6. 



1.340 (A. M.) 

 1.330 (A. M.) 

 1.235 (P. M.). 



1.383 •• 



1 . 400 



1.420 



1-435 



1-485 •■ 



1 . 502 . 



1-545 ■ • 



1 . 564 



1.665 



1.689 



1-730 



1.768 



1.802. 



1.874 



1.897 



2.050 



2 . 097 



2 . 280 . 



2.338 



2.415 



2.480 



2.567. 



2.943 



3.055 



3-280 



3420 



3.760 



3.90 



4.05 



4-45 



.1783 



,1978 

 1703 

 1757 



1463 

 1500 



1359 

 1359 



.0851 



• 0945 



1. 150 



.635 

 .640 



.404 

 .388 



.2471 



(1.200) 



1. 013 



-995 



• 949 



•975 



(•830) 



(•875) 



.780 

 .798 



(.660) 

 (.648) 



.668 

 .702 

 .608 

 .633 



(.'6i3) 



1.232 



I.084t 



1. 000 



1. 019 



.947 

 •956 



,504 



218 

 193 

 190) 



.990 



.983 

 •987 

 .993 



1.020 



.964 

 .967 



•775 

 .770 



• 6825 

 .680 

 .6325 

 •6493 



.5220 



General mean 



Omitting observations Nos. 2 and 18. 



lot 



991) 



984 



995 



035 



on 



993 



001 



018 



01 



994 

 966 



02 

 969 

 040 

 024 



930) 

 034 



006 

 005 



* Constant of instrument different from preceding column, allowance being made for the 

 removal of the glass. 



t Ammeter probably stuck. 

 () Result on sun obtained by subtracting sky from sun and sky combined. 



