CHAPTER III 



SPARKING POTENTIAL IN A UNIFORM ELECTRIC FIELD 



20. Description of phenomena accompanying discharges ; 

 sparking potential. 



The various phenomena relating to the discharge 

 of electricity through gases at low pressures have been 

 investigated experimentally by many physicists, and the 

 principal facts in connection with them have been well 

 established. With regard to the sparking potential, 

 it will be seen that the researches which have been 

 carried out on the effects of collisions, suggest an 

 obvious method 1 of obtaining a simple theory of the 

 sparking potentials for parallel plates in a gas at 

 different pressures and also a consistent explanation of 

 the large difference that exists between the sparking 

 potential and the potential required to maintain the 

 discharge at the higher pressures. 



The principal features of the phenomena which are to 

 be considered may be briefly stated as follows : When 

 a potential difference is established between two elec- 

 trodes in a gas, the gas behaves as an insulator unless 

 the potential exceeds a certain definite value, which is 

 called the sparking potential. The sparking potential 

 is very sharply denned, and it has been found that the 



1 See papers by the author in Electrician, April 3, 1903, and 

 Philosophical Magazine, November, 1903, and March, 1905. 



E 2 



