512 BELL SYSTEM TECHNICAL JOURNAL 



usually yields zero or slightly positive values. What experimental 

 data there are indicate small positive temperature coefficients for 

 atomic polarizations. 



One of the principal achievements of the Debye theory of dipole 

 polarizations has been the manner in which it explains the large 

 negative temperature coefficients of polarization of many liquids. 

 Debye showed that the variation of polarization with temperature 

 could be expressed by the relation P = A -{■ {BIT), in which the 

 constant ^ is a measure of the instantaneous polarizations which are 

 independent of temperature and 5 is a measure of the dipole polariza- 

 tions. In a liquid or gas the molecules are continuously undergoing 

 both translational and rotational motion, and the result of this thermal 

 motion is to maintain a random orientation of molecules. The action 

 of the electric field in aligning the dipoles is opposed by the thermal 

 motion which acts as an influence tending to keep them oriented at 

 random. As the temperature decreases, the thermal energy becomes 

 smaller and the dipole polarization becomes larger, resulting in a 

 negative temperature coefficient of dielectric constant. 



The effect of temperature upon interfacial polarizations has not 

 been experimentally investigated to an extent at all comparable with 

 that of dipole polarizations. However, interest in the interfacial or 

 ionic type of polarization has increased considerably in the past few 

 years, and it has applications of some importance. Among these is 

 diathermy which is becoming of considerable importance as a thera- 

 peutic agency. 



The foregoing qualitative description of the behavior of the di- 

 electric constant and the type of information regarding molecular 

 structure which has been derived from it will be followed in the next 

 section by the derivation of some of the quantitative relationships 

 which are common to all polarizations of the absorptive type. 



