NO. 3 RADIATION OF THE ATMOSPHERE — ANGSTROM 49 



complete and rather qualitative than quantitative, at least as regards 

 water vapor. I have reason to believe that the careful observations 

 of Fowle, of the Astrophysical Observatory of the Smithsonian 

 Institution, will in the near future fill this gap. 



From analogy with the absorbing qualities of water vapor, I think 

 one may conclude that an extrapolation of the radiation curve (fig. 5) 

 down to zero is liable to give an approximately correct result. The 

 extrapolation for the radiation of a perfectly dry atmosphere at 20° C. 

 gives a value of 0.281, which corresponds to a nocturnal radiation 

 of 0.283 at the same temperature. At o° C. the same quantities are 

 0.212 and 0.213 cal. and at —8° they have the values 0.190 and 0.191, 

 respectively. The latter value comes near the figure 0.201, obtained 

 by Pernter on the top of Sonnblick at —8° C. temperature. 



These considerations have given a value of the radiation from a 

 perfectly dry atmosphere, and at the same time they lead to an ap- 

 proximate estimate of the radiation of the upper atmosphere, which 

 is probably chiefly due to carbon dioxide and a variable amount of 

 ozone. The observations indicate a relatively high value for the 

 radiation of the upper layers — almost 50 per cent of the radiation 

 of a black body at the prevailing temperature of the place of observa- 

 tion. Hence the importance of the upper atmosphere for the heat- 

 economy of the earth is obvious. The effect at places near the earth's 

 surface is of an indirect character, as only a small fraction of the 

 radiation from the upper strata reaches the earth's surface. But the 

 importance of the upper layers for the protecting of the lower water- 

 vapor atmosphere — the troposphere — against loss of heat, is entirely 

 similar to the importance of the latter for the surface conditions of 

 the earth. If we could suddenly make the upper atmosphere dis- 

 appear, the effect would scarcely be appreciable at the earth's surface 

 for the first moment. But the change would very soon make itself 

 felt through a considerable increase in the temperature gradient. 

 At places situated a few kilometers above the earth's surface, as, for 

 instance, the summits of high mountains, the temperature would fall 

 to very low values. As a consequence the conduction and convection 

 of heat from the earth's surface would be considerably increased. 

 Keeping these conditions in view, and in consideration of the high 

 value of the radiation of the upper atmosphere — the stratosphere — 

 indicated by the observations, I think it very probable that relatively 

 small changes in the amount of carbon dioxide or ozone in the atmos- 

 phere, may have considerable effect on the temperature conditions 

 of the earth. This hypothesis was first advanced by Arrhenius, that 



