246 Prof. S. Arrhenius on the Influence of Carbonic Acid 



a rearrangement of the figures in greater groups, with con- 

 sequent recalculation. 



A circumstance that argues very greatly in favour of the 

 opinion that the absorption- coefficient given in Table II. 

 cannot contain great errors, is that so very few logarithms 

 have a positive value. If the observations of Langley had 

 been wholly insufficient, one would have expected to find 

 nearly as many positive as negative logarithms. Now there 

 are only three such cases, viz., for carbonic acid at an angle 

 of 40°, and for water-vapour at the angles 36 c, 45 and 

 36°*15. The observations for 40° are not very accurate, 

 because they were of little interest to Langley, the corre- 

 sponding rays not belonging to the moon's spectrum but only 

 to the diffused sunlight from the moon. As these rays also 

 do not occur to any sensible degree in the heat from a body 

 of 15° C, this non-agreement is without importance for our 

 problem. The two positive values for the logarithms belong- 

 ing to aqueous vapour are quite insignificant. They correspond 

 only to errors of 02 and 1*5 per cent, for the absorption of 

 the quantity W = l, and fall wholly in the range of experi- 

 mental errors. 



It is certainly not devoid of interest to compare these 

 absorption-coefficients with the results of the direct observa- 

 tions by Pascben and Angstrom*. In making this com- 

 parison, we must bear in mind that an exact agreement 

 cannot be expected, for the signification of the above co- 

 efficients is rather unlike that of the coefficients that are or 

 may be calculated from the observations of these two authors. 

 The above coefficients give the rate of absorption of a ray 

 that has traversed quantities of carbonic acid (K = l*l) and 

 water-vapour (W -03); whilst the coefficients of Paschen and 

 Angstrom represent the absorption experienced by a ray on 

 the passage through the first layers of these gases. In 

 some cases we may expect a great difference between these 

 two quantities, so that only a general agreement can be 

 looked for. 



According to Paschen's figures there seems to exist no 

 sensible emission or absorption by the aqueous vapour at 

 wave-lengths between 09/a and 1*2 /j, (corresponding to the 

 angle of deviation 40°). On the other hand, the representa- 

 tion of the sun's spectrum by Langley shows a great many 



* Paschen, Wied. Ann. 1. p. 409, 1893 ; li. p. 1, lii. p. 2C9, and liii. 

 p. 334, 1894, especially vol. l. tab. ix. tig. 5, curve 1 for carbonic acid, 

 curve 2 for aqueous vapour. Angstrom, Bihang till K. Vet.-Ak. Hand- 

 lings, Bd. xv. Afd. 1, No. 9, p. 15, 1889; Ofversigt af K. Vet.-Ak 

 lorhandl. 1889, No. 9, p. 553, 



