no. 3 



RADIATION OF THE ATMOSPHERE ANGSTROM 



85 



tive index for- the long - waves here considered to be 1.33, a value 

 that is based upon measurements by Rubens and myself. The 

 upper curve is taken from figure 12, curve IV. This same curve 

 corresponds to a water-vapor pressure of 5 mm. The ratio between 

 the areas is 0.937, i. e., the water surface radiates under the given 

 conditions 93.7 per cent of the radiation from a black body. A 

 change in the water-vapor pressure will affect this ratio only to a 

 small extent. 



I will now assume that a black horizontal surface radiates to space, 

 and that the vertical distribution of the water vapor over the surface 

 satisfies the conditions for which our radiation formula holds (Chap- 

 ter III (2) ). Then the radiation can be computed provided the tern- 



Temperature. 



Fig. 16. 



perature is known. If the black surface is replaced by a water sur- 

 face the radiation will be only 94 per cent of its former value. The 

 latter radiation is given as a function of the temperature by figure 

 16, where I have applied the considerations made above to the in- 

 terval between — io° C. and +20 C. From the figure may be seen 

 how the radiation is kept almost constant through the increase with 

 rising temperature of the water-vapor content of the atmosphere. 

 There is only a slight decrease in the radiation with rising tern- 

 perature. 



The ideal conditions here imagined are probably more or less in- 

 consistent with the actual state of things. In the first place, the air 

 immediately above, the ocean is generally not saturated with water 

 vapor, the relative humidity being rarely more than about 90 per cent. 

 In the second place, it is not quite correct to assume that the average 

 distribution of the water vapor over the ocean is the same as the 





