ON THE FLOW OF FORCE. 



in equilibrium, has everywhere the same potential, this expression, 

 which implicitly contains masses relative to induced electricity, is also 





zero on the ground. The value of V A is then reduced to ^ . 



In general, then, to express the potential V at any point of the 

 field, we have 



(6) 



^-<m 



47- 



Thus, the potential at a point is equal to the sum of the quotients 

 obtained by dividing each of the acting masses by its distance from 

 the given point. 



28. ON THE FLOW OF FORCE. Let A (Fig. 3) be an equi- 

 potential surface, and </A an element of this surface at the point P. 

 Through the contour of this element let lines of force be drawn 



Fig. 3- 



which cut all the successive equipotential surfaces at right angles. 

 An orthogonal canal thus bounded by lines of force is called a tube 

 of force. 



The elementary tube of force, bounded by the contour of the 

 element */A, cuts from any surface S passing through the point P 

 an element of surface d. 



In P the electrical force F is perpendicular to dK; let F n be the 

 component of this force parallel to the perpendicular to the surface S ; 

 the angle of the two forces being equal to that of the two elements 

 of surface, we have 



whence 



