238 frof. S. Arrhenius on the Influence of Carbonic Acid 



absorption " *. This view, which was founded on too 

 wide a use of Newton's law of cooling, must be abandoned, 

 as Langley himself in a later memoir showed that the full 

 moon, which certainly does not possess any sensible heat- 

 absorbing atmosphere, has a " mean effective temperature " 

 of about 45° C.t 



The air retains heat (light or dark) in two different 

 ways. On the one hand, the heat suffers a selective dif- 

 fusion on its passage through the air ; on the other hand, 

 some of the atmospheric gases absorb considerable quantities 

 of heat. These two actions are very different. The selective 

 diffusion is extraordinarily great for the ultra-violet rays, and 

 diminishes continuously with increasing wave-length of the 

 light, so that it is insensible for the rays that form the chief 

 part of the radiation from a body of the mean temperature of 

 the earth J. 



* Langley, l Professional Papers of the Signal Service,' No. 15. " Re- 

 searches on Solar Heat," p. 123 (Washington, 1884). 



t Langley, "The Temperature of the Moon." Mem. of the National 

 Academy of Sciences, vol. iv. 9th mem. p. 193 (1890). 



X Langley, ' Prof. Papers,' No. 15, p. 151 . I have tried to calculate a 

 formula for the value of the absorption due to the selective reflexion, as 

 determined by Langley. Among the different formulae examined, the 

 following agrees best with the experimental results : — 



log«=6(l/X)+ C (l/X) 3 . 



I have determined the coefficients of this formula by aid of the method 

 of least squares, and have found — 



b= -0-0463, 



-0-008204. 



a represents the strength of a ray of the wave-length X (expressed in 

 fi) after it has entered with the strength 1 and passed through the 

 air-mass 1. The close agreement with experiment will be seen from the 

 following table : — 



X. 



« 1/7 ' 6 (ob,). 



1/7-6. 

 a (calc). 



Prob. error 



O-358/i 



0-904 



0-911 





0-383 



0-920 



0-923 



0-0047 



0-416 



0935 



0-934 





0-440 



0942 



0-941 





0-468 



0-9.oO 



0-947 



0-0028 



0-550 



0960 



0960 





0615 



0968 



0-967 





0-781 



0-978 



0977 





0-870 



0-982 



0980 



00017 



1-01 



0-985 



0984 





1-20 



0-987 



0-937 





1-50 



0989 



0-990 



00011 



2-59 



0-990 



0993 



00018 



