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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 71 



OBSERVATIONS AT DUSK 



Two sets of observations have been taken to show the decrease 

 of sky light at sunset. The first set was taken February 23, 1918, 

 at Hump Mountain. Here an artificial sunset, so to speak, took 

 place; for the mountain rose considerably above the observatory in 

 the west, and the sun disappeared at an altitude of about +12°. 

 The second set was taken December 10, 1918, at Calama, where the 

 sun disappeared at an altitude of about —30 minutes. In both cases 

 the whole sky was observed, with the sun shaded off and the glass 

 screen on. Observations were begun sometime before sunset and 

 were continued with some intervals until the galvanometer deflec- 

 tions were too small to read. 



Results were as follows : 



Hump Mountain, February 22, 1918 



Sky cloudless, little haze, little wind. 



Sun disappeared behind the hill 4" : 30" 



Time of sunset 5'':3i" 



30' H. A. 



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