232 ELEMENTARY LESSONS ON [CHAP. iv. 



capacity of condensers of all ordinary forms, in electro- 

 static units : 



Sphere: (radius = r. See Art. 247). 



c";4>. 



Two Concentric Spheres: (radii r and r', specific 

 inductive capacity of the dielectric K). 



r -r 

 Cylinder : (length = /, radius = r). 



Two Concentric Cylinders : (length = /, specific in- 

 ductive capacity of dielectric = /, internal radius 

 = r, external radius = r'. 



2 log* L 



r 

 Circular Disc : (radius = r, thickness negligible). 



Two Circular Discs: (like air condenser, Art. 48, 

 radii = r, surface = S, thickness of dielectric = , 

 its specific inductive capacity = k). 



or C = k. 



4?T0 



(The latter formula applies to any two parallel discs 

 of surface S, whether circular or otherwise, provided they 

 are large as compared with the distance b between 

 them.) 



278. Energy of Discharge of Leyden Jar or 

 Condenser. It follows from the definition of potential, 

 given in Art. 237, that in bringing up one + unit of 



