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VI. On the Reflection of Light in the Atmosphere. 

 By Professor R. Clausius. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



I NOTICE in the Proceedings of the Royal Society for Feb- 

 ruary an interesting communication by Messrs. Roscoe 

 and Baxendell "On the Relative Chemical Intensities of direct 

 'Sunlight and diffused Daylight at different Altitudes of the Sun/* 

 in which my theoretical investigations on the dispersion of light 

 in the atmosphere are mentioned. May I be permitted to com- 

 municate a few observations to which this paper have led me ? 



From calculations made partly by themselves and partly by 

 M. Wolkoff in Heidelberg, the authors have deduced the ratio 

 between the chemical intensities of direct sunlight and of diffused 

 daylight. The values thus obtained they have collated in the 

 following Table, with the results of a calculation which I made 

 under the supposition that the reflection of light in the atmo- 

 sphere is occasioned by vesicles of water*. 









Experiments 





Sun's 

 altitude. 



Calculated 

 (Clausius). 









Heidelberg. 



Cheetham 

 Hill. 



Owens 



College. 







20 



491 



0*35 



019 



010 



25 



0-896 



0-48 



0-20 



Oil 



30 



1-320 



0-65 



0-23 





35 



1-690 



0-82 



0-26 





40 



2032 



100 







50 



2-634 



1-37 







60 



3129 



1-60 







As the numbers in the column "calculated" do not agree 

 with the numbers deduced from experiments f, they conclude 

 hence " that the effect of the atmosphere upon the highly refran- 

 gible and chemically active solar rays is regulated by totally dif- 

 ferent laws from those founded upon the hypothesis of the 

 reflection by means of hollow vesicles of water." 



* Crelle's Journal, vols, xxxiv. and xxxvi. ; Poggendorff's Annalen, 

 vol. lxxii. p. 294. 



t I must here remark that an error occurs in this Table. I have deter- 

 mined the position of the sun by giving its zenith-distance ; and in the 

 Table the numbers which refer to the zenith-distances 80°, 7-5°, 70°, &c, 

 are given as if they referred to the sun's heights 20°, 25°, 30°, &c, instead of 

 to the heights 10°, 15°, 20°, &c. If this confusion had not arisen, the dif- 

 ferences between the calculated and observed values would have been 

 greater than the Table shows. 



