Photometric Observations of the Sun and Sky. 



277 



Table Gr. Showing Chemical Action of the Sun and of the whole 

 Sky, resolved on the Horizontal Plane, for various Altitudes of the 

 Sun (the Sky being perfectly clear from Cloud and Haze). 



The present paper contains my Dacca experiments and numbers 

 ived at by calculation therefrom. I have been for a year making 

 ilar experiments in England whenever the sky by its clearness 

 ffered any chance of a gcod observation ; but I have not been able 

 get any observation such that I should attempt to correct the 

 acca Table B thereby. I, therefore, am satisfied to publish the 

 iresent paper in its present form, leaving to others its extension by 

 .he help of further observations under a perfectly clear sky. 

 38. Postscript, \5th October, 1890. I have within the last few days 

 ade a number of observations with the octant actinometer, and have 

 also, by making a few sunstrips at different altitudes, compared the 

 times for the candle unit with those of the Dacca tables. These 

 bservations, though giving no numerically valuable results, strongly 

 confirm the views I have expressed in this paper, and I append a 

 statement of them. 



On the 10th October the sky was seemingly clear; but, the values 

 btained for [V] = [W] being much too high, I did not continue the 

 nervations. 



On the llth October I took a sunstrip at 12 h 8 m , the Sun's altitude 

 ing 31 30' ; comparing this afterwards with a candlestrip, I found 

 e time for the candle unit to be 8'5 seconds. Referring to the 

 acca table, I found the time for the same altitude, 31 30', to be 

 >'9 seconds. I therefore used this snnstrip for the observations in 

 he preceding table. I infer that, at least at 12 h 8 m , the sky on the 

 1th October was really clear. Some of the values in this table are 

 igher than those obtained by computation for i a . 



