37 6 



Note 10.- disruptive discharge 



uniformly, as it does between two infinite planes, then the resultant electro- 



y 

 motive intensity is R = . 



If, on the other hand, we suppose that the variation of the potential near 

 the surface of the disks is affected by unknown causes, we would get a better 

 estimate of the intensity by taking 



R- dV 

 R ~d^' 



V dV 

 Both and -^ diminish as the distance increases, approximating to the 



limit 66-940. 



This corresponds to a surface-density of 5-327 units of electricity per square 

 centimetre, and to a tension of 178-3 dynes per square centimetre. As the 

 ordinary pressure of the atmosphere is about a million dynes per square centi- 

 metre, the pressure with which the electricity tends to break through the air 



is only about -^ of the pressure of the atmosphere. 



If the electrodes are convex surfaces, whose radii of curvature, a and b, 

 are large compared with the least distance c between the surfaces, then if 



the greatest electric force at the surface whose radius is a will be equal to that 

 at either of two parallel plane surfaces at the same potentials whose distance 

 is s. 



