588 ELECTRICAL UNITS. 



607. ELECTROSTATIC SYSTEM. Quantity of Electricity [q\. 

 Coulomb's law gives, for the repulsion f exerted between two equal 

 masses q at the distance */, 



or 



-djf. 



From which is deduced, for the dimensions of the unit of 

 electricity, 



Surface density. Electrical displacement [a-]. The density is 

 the quantity of electricity for unit surface (18) ; the displacement 

 is the quantity which has traversed unit surface (126); we shall 

 have then, 



Electrical force. Strength of the field \H\. This is the force 

 which acts on unit mass at the point in question, which gives 

 for the dimensions of the unit, 



they are the same as that -of density, as could be foreseen from 

 Coulomb's theorem (35). 



The j##w of electrical force is the product of electrical force into a 



3 1 



surface; its dimensions are [L 2 M 2 T~ 1 ]. 



Specific inductive capacity []. The specific inductive capacity 

 is a number in the electrostatic system. 



Electromotive force or electrostatic potential \e\ The potential 

 of an electrical mass at a distance d, is the quotient of the mass 

 by this distance ; we have then 



Electrostatic capacity \c\. The capacity of a condenser is the 

 quotient of its charge by the difference of potential of the armatures, 

 and we have 



c- 9 -, or , = L. 



