141-143] 



Molecular Theory 



127 



" The particles of an insulating dielectric whilst under induction may be 

 compared... to a series of small insulated conductors. If the space round 

 a charged globe were filled with a mixture of an insulating dielectric and 

 small globular conductors, the latter being at a little distance from each 

 other, so as to be insulated, then these would in their condition and action 

 exactly resemble what I consider to be the condition and action of the 

 particles of the insulating dielectric itself. If the globe were charged, these 

 little conductors would all be polar ; if the globe were discharged, they would 

 all return to their normal state, to be polarised again upon the recharging 

 of the globe...." 



As regards the question of what actually the particles are which undergo 

 this polarisation, Faraday says* : 



" An important inquiry regarding the electric polarity of the particles of 

 an insulating dielectric, is, whether it be the molecules of the particular 

 substance acted on, or the component or ultimate particles, which thus act 

 the part of insulated conducting polarising portions." 



" The conclusion I have arrived at is, that it is the molecules of the 

 substance which polarise as wholes; and that however complicated the 

 composition of a body may be, all those particles or atoms which are held 

 together by chemical affinity to form one molecule of the resulting body act 

 as one conducting mass or particle when inductive phenomena and polari- 

 sation are produced in the substance of which it is a part." 



143. A mathematical discussion of the action of a dielectric constructed 

 as imagined by Faraday, has been given by Mossotti, who utilised a mathe- 

 matical method which had been developed by Poisson for the examination of 

 a similar question in magnetism. For this discussion the molecules are 

 represented provisionally as conductors of electricity. 



To obtain a first idea of the effect of an electric field on a dielectric of 

 the kind pictured by Faraday, let us consider a parallel plate condenser, 



I- + 



FIG. 46. 



* Experimental Researches, 1699, 1700. 



