8 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 66 



new fallen snow. In comparisons with the pyrheliometer it gave very 

 nearly equal results when corrected to vertical incidence. The reflect- 

 ing power of snow for combined sun and sky rays was found to be 

 70 per cent. 



Some of the results found from the measurements with Pyra- 

 nometer A. P. O. 5 are given in table II. We draw attention to the 

 results on cloudy and partly cloudy days, which indicate that the 

 sky light as a whole, on days when it is cloudy but not thick enough 

 to rain, is of the order of two or three times the intensity of the sky 

 light excluding the direct sun on clear days. 



The pyranometer is a very handsome instrument as constructed by 

 Mr. Kramer. It may be used readily by anyone equipped with the 



Table II. — Suviiiiary of Readings of February. 1916. North Tozver, 

 Smithsonian Institution, Pyranometer A. P. O. 5 



* Values in this column obtained by interpolating for " sky alone," subtracting interpolated 

 values from "sky and sun " and multiplying by secant Z. 



t Values in this column obtained by plotting logarithmically seven readings of pyrheliome- 

 ter A. P. O. 9 made at various times during the afternoon and interpolating from this plot 

 values to correspond with values of secant Z. 



