102 Cacly and Vinal — Electric Arc. 



rapid and powerful when the discharge takes place in a mix- 

 ture of hydrogen and acetone vapor. 



III. Strong evidence in favor of the glow-arc hypothesis is 

 derived from the measurement of the maximum potential dif- 

 ference assumed by the discharge during each cycle. By 

 means of -a calibrated spark-gap it was found that this maximum 

 does not rise above that characteristic of a glow discharge. A 

 new method was employed for keeping the gas in the neigh- 

 borhood of the spark-gap in a state of ionization. 



Scott Laboratory of Physics, 

 Wesleyan University, 

 June 3, 1909. 



[To be continued.] 



