Electrostatic Capacity of a Conductor. 1 1 3 



It is known that specific inductive capacity bears the 

 same relation to flow of force'- as conductivity does to a flow 

 of electricity^ Consider, therefore, the problem in current 

 electricity corresponding to the above electrostatical one. 

 An anode A is placed in a conducting medium in which are 

 placed several kathodes B, C, etc. Then in the phraseology 

 generally used for capacity, the conductivity of the anode 

 A would be spoken of, and it would be said that the 

 conductivity of A depended neither on the nature nor 

 the mass of A, B, C, etc., but only on their external 

 shape and their relative positions. Finally it would be 

 said that if the medium between A, B, C, etc., was not 

 a certain one, the result obtained by calculation from 

 this method of considering the phenomena would have to be 

 multiplied by a certain number, fixed for the medium in 

 question. Such a mode of viewing the facts is evidently 

 irrational, and tends to withdraw the attention from the 

 real principle, namely, that the conductivity under con- 

 sideration is that of the medium, and that the function of 

 the electrodes is simply to bound the portion of the medium 

 which is traversed by the current. Adapting this mode of 

 description to electrical capacity, tJie so-called capacity of 

 the conductor is the capacity of that portion of the dielectric 

 bounded by the conductors and traversed by the lines of 



specific inductive capacity of the medium, but it is not easy to see, from the 

 above assumptions, why this should be, or in other words, if only the quantity 

 of electricity on the suface of the sphere need be considered, why the 

 potential at the centre of the sphere due to a quantity of electricity on its 

 surface should depend on the nature of the medium outside the sphere. The 

 advantage of the method now advocated is that the medium between the 

 <:harged body and the corresponding induced charge is always kept in view. 

 " Flow of force along an air tube of force = F^fS where ^S is the perpendicu- 

 lar section of the tube and 

 F the mean value of the 

 force on that section. 

 -/i^-7rdq where dq is the quantity of 

 electricity at the commence- 

 » We have Q = C(Vi - V.J ment of the tube, 



or 4crQ = 4'77C(V, -\\) 

 or Flow of force = 4^0 x diff. of pot. 



