2 RADIO REFRACTIVE INDEX OF AIR 



molecule being one with a strong permanent dipole moment. He derives 

 the same result from both classical and quantum mechanical methods; 

 i.e., the polarizability is composed of two effects: one due to the distortion 

 of all of the molecules by the impressed field and the second arising from 

 an orientation effect exerted upon polar molecules. The polarization, P, 

 of a polar liquid under the influence of a high-frequency radio field is 

 given by 



P{o:) 



6 - 1 M 



£ + 2 p 



47riV 



ao + 



1 



3/cr 1 + iojrj 



(1.1) 



where : e is the dielectric constant, 



M is the molecular weight, 



p is the density of the liquid, 



A^ is Avogadro's number, 



ao is the average polarizability of the molecules in the liquid, 

 assuming no interaction between molecules, 



M is the permanent dipole moment, 



k is Boltzmann's constant, 



T is the absolute temperature, 



T is the relaxation time required for external field-induced orien- 

 tations of the molecules to return to random distribution 

 after the field is removed, 



CO = 2'wf where / is the frequency of the external field. 



One concludes from Debye's analysis that for external fields with fre- 

 quencies less than 100 Gc/s, wr « 1 with the result that (1.1) is written^ 



(1.2) 



The dispersive effect of the 22.5 Gc/s water-vapor absorption line is not 

 expected to be important below 30 Gc/s although, as shall be seen, experi- 

 mental evidence indicates some dispersion due to the 60 Gc/s absorption 



^ The effect of the relaxation time upon interpretation of measurements of dielectric 

 constant has been discussed by Saxton [1]; he has also given a description of measure- 

 ment techniques involved in the determination of dielectric constant during the war 

 years [3]. 



