4:66 M. 1. Pupin-^ Electrical discharges through poor 



of the static capacity at that point. Diminishing gradually 

 the e. m. f., the luminosity of the discharge diminished with it 

 and then stopped suddenly as if a critical point had been 

 suddenly reached. Reducing the e. m. f. gradually to zero 



and then gradually increasing it again, it was found that the 

 discharge would cease at a point much lower than the point 

 at which it would start again, the difference between the 

 two points diminishing considerably with the rapidity with 

 which these variations were made. The discharge will start 

 at a much, lower e. m. f. if solicited, that is to say if the long 

 tube is touched at one or more points. A wire bent in the 

 shape of a Leyden jar discharger does very good service as a 

 discharge "solicitor." 



The discharge was similarly affected by varying the capacity. 

 Performing the last experiment, but with the small vacuum 

 jar c cl given in fig. 7, it was found that with a given potential 

 (just above the critical point) the discharge did not start until 

 the bulbs c d had reached a certain depth and then it started 

 suddenly. Raising the bulbs gradually, and therefore dimin- 

 ishing the capacity, the discharge became fainter and fainter,, 

 but it did not cease until the bulbs were entirely lifted out of 

 the water. On immersing again, the discharge did not start 

 until a certain depth was reached. The depth at which the dis- 



