SPARKING POTENTIAL IN A UNIFORM ELECTRIC FIELD 59 



TABLE XXI. 

 HELIUM (before purification with liquid air). 1 Sparking Potentials, 



The sparking potentials in volts are also given in 

 the following curves, figure 11, the abscissae being the 

 product of the pressure and the distance between the 

 plates. 



The accuracy of the theory is thus established over a 

 range of pressures extending from the critical pressure 

 to a pressure twelve times as great for any distance 

 between the plates. The theory has not been tested for 

 pressures below the critical pressure, as the values of 

 a and ft were not determined for the lower pressures for 

 the reasons already explained. 



It may readily be seen from the theory that the 

 potential SX is a function of >S only, and con- 

 sequently that Paschen's law is satisfied. For if v 

 denotes the theoretical sparking potential SX and m 

 the product pS which is proportional to the quantity 



of gas between the electrodes, then a=pj(]=pj(}, 



1 The sparking potentials for pure helium are much lower; 

 the minimum does not exceed 200 yolts, 



