510 BELL SYSTEM TECHNICAL JOURNAL 



are purely arbitrary. Anomalous dispersion due to dipole polariza- 

 tions has been observed at power frequencies while that due to inter- 

 facial polarizations has been observed at radio frequencies. The two 

 types of polarizations may in fact give rise to anomalous dispersion 

 in the same frequency range in a given dielectric. 



Proceeding to still higher frequencies in Fig. 1 other regions of 

 dispersion appear in the infra-red and visible spectrum. These 

 regions show a combination of normal optical dispersion, in which the 

 dielectric constant, or better now the refractive index, increases with 

 frequency, and anomalous dispersion in which it decreases. The 

 dispersion in the visible range of frequencies is predominantly normal 

 (anomalous dispersion being confined to relatively narrow frequency 

 bands) whereas in the electrical range the reverse is true, normal 

 dispersion not being observed ; the infra-red represents an intermediate 

 region. Dipole and interfacial polarizations are not represented in 

 the dispersion in the optical range, the dielectric constant (or refractive 

 index) in the visible being due to electronic polarizations and in the 

 infra-red to electronic and atomic polarizations. 



The curves plotted in Fig. 1 are merely schematic and the relative 

 magnitudes of the different contributions to the dielectric constant 

 are therefore arbitrary. However, experimental results indicate that 

 the contribution eg of the electronic polarization to the dielectric 

 constant is limited to values between 2 and 4 except for certain in- 

 organic materials, since very few organic solids or liquids are known 

 which have refractive indices in the visible spectrum which are greater 

 than 2 or less than 1.4. The contribution e^ of atomic polarizations 

 to the dielectric constant is in general small and is usually negligible, 

 as has been indicated on the curve, although the possibility exists of 

 special cases occurring in which the infra-red refractive indices are 

 very high. The contributions tp and «/ of dipole and interfacial 

 polarizations to the dielectric constant may vary greatly from one 

 material to another, depending upon the symmetry of the molecule 

 and the physical structure of the dielectric. From the above men- 

 tioned limitations on the contribution to the dielectric constant which 

 can be expected from electronic and atomic polarizations, it is apparent 

 that the explanation of values of e higher than 3 to 4, at least in organic 

 materials, requires the existence of some absorptive polarization such 

 as arises from dipoles or interfacial effects. Thus all of the liquids 

 which have high dielectric constants such as H2O (78), alcohol (24), 

 nitrobenzene (34) have been shown to contain polar molecules. 



The lower part of Fig. 1 shows a maximum in the absorption for 

 each type of dielectric polarization. The absorption, at least in the 



