ELECTRICAL ABSORPTION. 95 



is discharged, the disposable electricity which disappears in the 

 discharge is sometimes far below the whole of that which it 

 possesses ; it is known moreover that we can successively obtain a 

 greater or less number of discharges of decreasing intensity. 



It appears difficult in the present state of science to account for 

 this phenomenon. Everything seems to point to its being due to a 

 progressive change in the structure of the dielectric, to a particular 

 deformation under the influence of causes which produce polarization; 

 a deformation which becomes permanent as in an imperfectly elastic 

 body, and after which the body does not immediately revert to its 

 original state when the cause has ceased to act. 



This view of the matter is confirmed by the facts that all the 

 circumstances which, in the case of a mechanical deformation, 

 favour the return of a body to the normal state such as blows, 

 rapid variations of temperature, and the like, appear also to accele- 

 rate the disappearance of the residual charge, and its return to the 

 neutral state. 



110. POLARIZATION OF THE DIELECTRIC. Although Faraday's 

 experiment is incompetent to settle the question of actions at a 

 distance, it shows unequivocally the part played by the medium in 

 electrical phenomena. We are thereby led to assume that, in 

 electrical induction, the medium acquires a state of polarization 

 analogous to that observed in soft iron when under the influence 

 of a magnet. 



In order to explain magnetism, Poisson made a hypothesis which 

 was transferred to the study of electrical phenomena by Mossotti, 

 and then adopted by Faraday. This hypothesis consists in assuming 

 that the magnetic medium, or the dielectric, is made up of particles, 

 which may be spherical for instance, which are absolute conductors, 

 and are disseminated in a non-conducting medium. 



" If the space round a charged globe were filled with a mixture 

 of an insulating dielectric, as oil of turpentine or air, and small 

 globular conductors as shot, 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 polarized again upon the recharging of the globe." 

 (Faraday, Experimental Researches , Series xiv., 1679.) 



Sir W. Thomson has shown that, without making any hypothesis 

 as to the constitution of the medium, it is sufficient to assume that 



