the Occurrence of Enhanced Lines in the Arc. 863 



one of their characteristic features in the capacity spark. 

 There is, however, a further striking similarity between 

 the spectra given by the capacity spark and the first phase 

 of a water arc — namely, the character of the hydrogen lines 

 is the same. In both sources the lines of the Balmer series 

 are considerably broadened. As is well known, these lines 

 are narrow and sharp with slow discharges under low 

 potential gradients, such as the ordinary coil discharge 

 through a vacuum tube or the self-induction spark through 

 hydrogen at atmospheric pressure *. 



With regard to the role played by the liquid films, the 

 results of our experiments with electrolytes have shown 

 clearly that they do not act as dielectrics. It seems to us 

 more probable that they merely serve to retard the formation 

 of the arc flash and in this way allow the electric field, which 

 becomes momentarily established between the electrodes, to 

 attain values comparable to those obtained in a capacity 

 spark. 



Thus, not only the particular state of the electrical con- 

 ditions arising from our special experimental arrangement, 

 but abo the observed character of both hydrogen and metal 

 lines point to the existence of strong electric fields during 

 the first phase of a water arc. This conclusion seems to be 

 strongly supported by our observations of the decomposition 

 of the He line by the electric field, as recorded in § 7. The 

 value of the electric field as derived from the amount of dis- 

 placement of the outer components was found to be in good 

 agreement with that obtained by direct calculation, so that 

 the existence of strong electric fields during the initial stages 

 of an arc flash appears to be highly probable. A further 

 fact in support, of this contention seems to be provided by 

 the peculiar behaviour of the lines of the Rydberg series of 

 magnesium. These lines are strongly broadened towards 

 the red during the early stages of a water arc, but they 

 appear without wings in a stable arc in nitrogen with an 



electric field of only about 150 ^-A Now, as Messrs. Taka- 



cm. 



mine and Kokubu have shown |, these lines are precisely 

 displaced towards the red in a strong electric field. As we 

 have further shown, the spark line X4481, which is symme- 

 trically broadened during the first phase of a water arc with 

 a strong electric field, appears as a very narrow line in the 



* Hernsalech, Comptes Rendus de V Academic des Sciences, t. cxxix. 

 p. 288 (1899). 



t Takamine and Kokubu, Memoirs of the College of Science 

 (Kyoto Imperial University), vol. iii. p. 178 (1918). 



