by a Charged Condenser moving through Space. 165 



Now there are two distinct classes of action which will 

 explain the existence of the quantity K. We may consider 

 that the electric force causes a separation of positive and 

 negative electricity in each atom or molecule, giving rise to 

 something equivalent to a doublet, or we may imagine the 

 doublets to exist even in the absence of the electric force, in 

 which case they will be orientated at any instant in all sorts 

 of directions, the effect of the electric force being to give 

 them a preference towards an orientation of their axes in 

 one particular direction. We shall first proceed to develop 

 the consequences of the former hypothesis. 



Considering the two condenser plates referred to above, 

 with the slab of dielectric between them, we are to look upon 

 the electric force as causing an electrical separation, giving 

 rise to a series of doublets, arranged in the manner shown 

 (fig. 5). Now the tubes of force from C do not pass con- 

 tinuously through the dielectric, most of them, or possibly all, 



Fisr. •">. 



+ 



/' 



,: c> 



end on some or other of the negative charges on the doublets 

 on the surface of A, and just as many tubes emanating from the 

 positive elements of these doublets are so to speak freed, 

 thus being at liberty to carry on the flux in the direction 

 from A to B. If we were to cut a cylindrical hole in the 

 •dielectric with its axis perpendicular to A, and of length 

 small compared with its cross-section, and if we were to 

 measure the electric intensity in this hole, we should get 

 Aire 2 times the ordinarily denned polarization or number of 

 tubes of force per square centimetre *, we should get the 



* The polarizatiou is here in electromagnetic units. 



