118 Trans. Acad. Sci. of St. Louis. 



original system. Here, however, we meet with complica- 

 tions. The electrified surface must break up into separate 

 closed sheets, surrounding the various bodies of the system. 

 Some of these surfaces may surround bodies which were orig- 

 inally positively charged, and others bodies which were nega- 

 tively charged. The charge on the collapsing surface is, 

 however, all of one sign. It is like a case where equal terms 

 of unlike sign in an equation have destroyed each other dur- 

 ing an operation. They will not replace themselves when 

 the operation is sought to be reversed. If, however, we 

 intelligently restore the charges to the separating sheets 

 of the collapsing surface until we have reproduced 

 the original electrification, then the energy which 

 we have applied to the surface is the energy of the 

 system. But all of this leaves untouched the question 

 concerning the nature of the force against which we have 

 been working. There is reason to believe that it is not 

 mutual repulsions between the elements of the electrification. 

 There is reason to believe that it is a reaction between the 

 electrification and a stressed condition which is impressed 

 upon each element of the medium, as soon as it becomes 

 external to the surface. 



The electrical system is in fact produced by forcing the 

 charges upon the surfaces of the cavities in the medium 

 which the bodies occupy, and the condition of stress is 

 propagated outwards and is maintained in some manner at 

 present unknown. 



It is evident that the evaluation of the volume integrals 

 involved in determining perviance, resolves itself into a deter- 

 mination of electrostatic capacity. This is capable of direct 

 determination by discharges through a ballistic galvanometer. 

 As the same integrals are involved in determining magnetic 

 permeance, it seems feasible to apply this method to a 

 study of many cases of leakage from magnetic circuits. 

 It would only be necessary to construct wooden or other 

 models having conducting surfaces, and having the forms to 

 be investigated. 



For resistance to electric induction or the reciprocal of 



