CHAPTEK IV 



THEORY OF ELECTRIC DISCHARGES IN FIELDS OF FORCE 

 WHICH ARE NOT UNIFORM 



25. Description of phenomena to be investigated. 



The theory may also be applied to discharges 

 between electrodes in gases in which the electric force 

 varies from point to point along the path of the current ; 

 but in these cases the investigations cannot be carried 

 out so completely as those which deal with the sparking 

 potential in a uniform field between two parallel plates. 

 Thus the potential required to produce a point discharge 

 cannot be expressed in a form that admits of being 

 compared with experimental results; but it can be 

 shown from the theory that the potential is smaller 

 when the point is negative than when the point is 

 positive throughout the range of forces and pressures 

 for which a and j3 have been determined. Another case 

 which is of interest is the potential required to maintain 

 a current between two parallel plates. When the 

 current is small the uniformity of the field is not 

 appreciably disturbed by the charge in the gas, so that 

 the potential required to maintain the current is the 

 same as the sparking potential. But when the current 

 increases the charge in the gas increases the force near 

 the negative electrode, and under these circumstances it 

 can be shown that the potential between the electrodes 

 which would maintain the current is less than the 



