424 



Mr. J. Buchanan. 



[May 27, 



with V. Let us denote by ( C ^\ the value of ^= when V=0; then 



VctV/o ftV 



according to the view adopted in this paper, (jjj^ is a quantity 



which has a value characteristic of each material, and may be 

 regarded as a property of each material in the same sense as, for 

 instance, the index of refraction. 



Let now the specific inductive capacity of the dielectric be increased 

 by £K. Thus the tendency is for the dielectric to become electrified 

 with a quantity of electricity — 



\dVjo 



This tendency being equal in all directions there is no resultant 

 electrification. If, however, another dielectric is put into close con- 

 tact with the first, dissymmetry is introduced. Denoting by the 

 suffixes ( 1 ) and ( 2 ) the quantities relating to the two dielectrics, and 

 by AE the electrification, we have initially, 



f ; (8.) 



2 \dVjo \dVjoJ 



These two equations express my view of the mode in which electri- 

 fication begins when two dielectrics are put into contact and their 

 specific inductive capacities are altered. The change of specific 

 inductive capacity may take place either by pressure or by friction — 

 with liquids it is probable that only the heating effect of friction can 

 influence the results. 



According to what law the electrification goes on increasing when 

 once started is a point still to be cleared up, the value for any 

 material of the quantity tt having still to be worked out experi- 

 mentally. 



Before discussing (8) it is convenient here to notice that when two 

 bodies are in very close contact, the capacity of the system that con- 

 sists of the two opposed surfaces and the extremely small distance 

 between them, must be very great indeed. If then at any moment 

 Q be the charge on either of these opposed surfaces and C denote the 

 capacity of the system, then (6) becomes — 



\dV ' dKj 



dir , 



7? nearly ' 



