.">:'>4 F. W. Very — Note on, Atmospheric Radiation. 



Near the earth's surface, the absorption of terrestrial radia- 

 tion replaces that of the sun's rays to a great extent, because 

 the absorbable part of the latter has already been removed by 

 the upper air, except as the dust of the lower air absorbs radia- 

 tion of every wave-length. The terrestrial radiation is chiefly 

 effective in warming a shallow layer of air (1) near the ground, 

 and its absorbable rays are soon sifted out in passing through 

 the lower humid layers; but it is also efficient at any level 

 where there is cloud and where the regions of absorption in 

 the spectrum of terrestrial radiation are much broader. 

 Emphasizing this importance of heat from absorption of ter- 

 restrial radiation by aqueous vapor, it is placed first on the list 

 in the enumeration of heat sources for the superficial layers. 



IJ, = /i t + /i c + /i v + h„ + h t + h e ± //„. 



The heat thus acquired may be removed by evaporation of 

 precipitated water particles ( — h e \ by atmospheric radiation 

 (—A,), by convection (— h c .) and by penetration ( — A,,.). If 

 there is thermal equilibrium, 



at level (3), h s + h, + h p ± /> q - (h, + h ]tl ) = 0, 

 « « (2), H 2 - (A e + h t + /*,, + h,,) = 0, 

 « " (1), H, - (/*. + h r + // c , + / V ) = 0. 



Except in the upper air, the distance through which atmos- 

 pheric radiation can proceed before it is reabsorbed by the air, 

 is so small that convection and penetration might be expected 

 to supersede radiation as available modes of thermal transfer- 

 ence from one body of air to another. We are at last able to 

 apply a critical test to this supposition . 



The study of the vertical distribution of thermal losses in 

 the earth's atmosphere which Professor Bigelow has made,* 

 permits for the first time a comparison of atmospheric radia- 

 tion, transferred from layer to layer in the free air, with that 

 computed from laboratory measures. 



The radiation from a layer of pure dry air, 1 meter in depth, 

 and having an excess of temperature of 10° C, may be taken 

 as equivalent to a transference of 0*00006 gram-water-degree- 

 Centigrade units of heat per second through each square cen- 

 timeter of surface.f Bigelow divides the atmosphere into 

 layers 1000 m. deep. The difference of temperature at the top 

 and bottom of each layer is somewhat less than 10°, varying in 

 fact between 5° and 7°C. throughout a considerable part of the 

 first 10,000 meters. If radiation (R) from layer to layer is 



* Frank H. Bigelow — " The Thermodynamics of the Earth's Non-adiabatic 

 Atmosphere." this Journal, xxxiv, 515-532. 



f Frank W.Very — "Atmospheric Radiation." Bulletin G, U. S. Weather 

 Bureau, p. 112, 1900. 



