40$ Polarization of Dielectrics in a Steady Field of Force. 



tljie radium. The experiment was repeated with the con- 

 ditions varied in several ways with always the same result. 



It would appear from this that the electrical movement in 

 a dielectric when isolated in the field is entirely confined to 

 the molecule, and is therefore neither metallic nor electrolytic 

 in type, but is the continued displacement of the atomic 

 charges to a greater degree of separation than has been 

 hitherto recognized. 



It may be remarked here that the high values of the 

 dielectric constants obtained in the paper are confirmed by 

 measurements on electric cables. Ashton * found that an 

 ozokeritized rubber cable charged at 206*5 volts for 7200 

 seconds, absorbed 13'8 X 10 " 5 coulomb. From the given 

 dimensions the dielectric constant corresponding to this is 

 13*1. In this case also the slow polarization was elastic in 

 type, as shown by the fact that the quantity discharged on 

 short circuit was just twice that absorbed at constant 

 potential. 



It was early suggested by Mossotti that the behaviour of a 

 dielectric can be explained on the assumption that it is made 

 up of isolated conducting spheres. On any of the present 

 electronic theories of matter the separation of charge under 

 the influence of the field gives an arrangement similar to 

 this. 



It is now suggested that the first stage of polarization pro- 

 duces such a charged system, but that it differs from a system 

 of conductors in that the charges undergo further separation 

 automatically by reason of the attraction and quasi-elastic 

 approach of opposite charges on adjacent molecules. The 

 limit of the first stage of rapid polarization is that of the 

 re-arrangement of atomic charge within the molecule, that 

 of later stages the establishment of electrical strain throughout 

 the mass under new conditions of internal stress set up by the 

 first polarization. 



The range of the dielectric constant in the first stage may 

 be taken as the intercept on the vertical axis in fig. 2. 

 Writing this K , it is of interest to compare it with the 

 values found for the same substances in alternating fields t, 

 as in Table III. The influence of frequency may from this 

 be anticipated. For those substances in which the ratio is 

 nearly unity it will be at low frequencies small, but for 

 the first few in the list a greater change may be expected 



* A, \V. Ashton, Phil. Mag, no. 62, 1901, p. 501, " On the Resistance 

 of Dielectrics." 



t Vide Roy. Soc. Proc. A. vol. lxxxii. p. 422 et seq. 



