NO. 3 RADIATION OF THE ATMOSPHERE ANGSTROM 35 



dent that there must be a very close relationship between the two 

 functions. In the figures the humidity values are plotted in the 

 opposite direction to the radiation values. Plotting in this way we 

 find that the maxima in the one curve correspond to the maxima in 

 the other and minima to minima, which shows that low humidity and 

 high effective radiation correspond and vice versa. 



The observations of table I are now arranged in table II in such 

 a way that all the radiation values that correspond to a water-vapor 

 pressure falling between two given limits, are combined with one 

 another in a special column. The mean values of humidity and 

 radiation are calculated and plotted in a curve aa, figure 3, which 

 gives the probable relation between water-vapor pressure and radia- 

 tion. Tables I and II show that the temperature of the air, and con- 

 sequently also that of the radiating surface, were almost constant 

 for the different series and ought not, therefore, to have had any 

 influence upon the form of the curve. 



The smooth curve of figure 3 gives the relation between effective 

 radiation and humidity. If we wish to know instead the relation 

 between what we have defined as the radiation of the atmosphere 

 and the humidity, we must subtract the value of the effective radia- 

 tion from that of the radiation of a black body at a temperature of 

 20 . The curve indicates the fact, that an increase in the water con- 

 tent of the atmosphere increases its radiation and that this increase 

 zvill be slozver with increasing vapor pressure. It has been pointed 

 out in the theoretical part that this is to be expected from the condi- 

 tions of the atmosphere and from the laws of radiation. The relation 

 between effective radiation and humidity can further be expressed 

 by an exponential formula of the form : 



R = 0.109 + 0.1 34 • e-°- 1Qp 

 or 



i? = 0.109 + 0.134- io^ - 957 " 1 ' • 



For the radiation of the atmosphere we get 



^ = 0.453-0.134 -(TO- 10 " 



That the radiation of the atmosphere, as a function of the water- 

 vapor pressure, can be given in this simple form is naturally due 

 to the fact that several of the radiation terms given through the 

 general expression (3), chapter III, have already reached their limit- 

 ing values for relatively low values of the water- vapor density. These 

 terms, therefore, appear practically as constants and are in the 

 empirical expression included "in the constant term. 



