SECT, xxvm.] ELECTRICAL INTENSITY. 315 



bodies. Since electricity can only be in equilibrio from the 

 mutual repulsion of its particles, which, according to these 

 experiments, varies inversely as the square of the distances, 

 its distribution in different bodies depends upon the laws of 

 mechanics, and therefore becomes a subject of analysis and 

 calculation. Although the distribution of the electric fluid 

 has employed the eminent analytical talents of M. Poisson 

 and Mr. Ivory, and though many of their computed pheno- 

 mena have been confirmed by observation, yet recent experi- 

 ments show that the subject is still involved in much difficulty. 

 Electricity is entirely confined to the surface of bodies ; or, if 

 it does penetrate their substance, the depth is inappreciable; 

 so that the quantity bodies are capable of receiving does not 

 follow the proportion of their bulk, but depends principally 

 upon the form and extent of surface over which it is spread: 

 thus the exterior may be positively or negatively electric, 

 while the interior is in a state of perfect neutrality. 



It appears, from the experiments of Mr. Snow Harris, that 

 a given quantity of electricity, divided between two perfectly 

 equal and similar bodies, exerts upon external bodies only 

 one-fourth of the attractive force -apparent when disposed 

 upon one of them ; and, if it be distributed among three equal 

 and similar bodies, the force is one-ninth of that apparent 

 when it is disposed on one of them. Hence, if the quantity 

 of electricity be the same, the force varies inversely as the 

 square of the surface over which it is disposed ; and, if the 

 surface be the same, the force varies directly as the square 

 of the quantity of the electric fluid. These laws, however, do 

 not hold when the form of the surface is changed. A given 

 quantity of electricity disposed on a given surface has the 

 greatest intensity when the surface has a circular form, and 

 the least intensity when the surface is expanded into an inde- 

 finite right line. The decrease of intensity seems to arise 

 from some peculiar arrangement of the electricity depending 

 on the extension of the surface, and has been considered by 

 Volta to consist in the removal of the electrical particles 



