8 64 Mr. G, A. Hemsalech and the Gomte de G-ramont 



on 



nitrogen arc with a feeble electric field. We therefore 

 venture to suggest that the symmetrical broadening of the 

 spark line A, 4481 and the red wings of the lines of the Rydberg 

 series observed during the first phase of a ivater arc are a 

 manifestation of the Stark effect. 



Since both the emission and the character of the spark lines 

 are independent of the nature of the liquid used, we have no 

 hesitation in assuming that the explanation which we have 

 given for their origin in the water arc holds equally good for 

 arcs with paraffin oil, alcohol, glycerin, etc. Further, as we 

 have already shown in § 6, the emission of spark lines at the 

 instant of striking an arc in a gaseous medium without 

 the intervention of a liquid film may be most satisfactorily 

 explained by assuming the transitory existence between the 

 poles of a rarefied space caused by the rapid recession of 

 the upper electrode. By temporarily preventing chemical 

 reactions between the metal vapour and the gases of the 

 medium this rarefied space would, like the liquid films, retard 

 the formation of the arc and thus permit the momentary 

 establishment of high potential gradients along the path of 

 the discharge. 



We now proceed -to consider the course of events during 

 the second phase of an 80 volt water arc. This phase begins 

 at the instant of destruction of the water film, and the distance 

 between the electrodes is then 0*10 mm. Thus the intensity 



of the applied electric field at this moment is only 8000 ^L_L. 



As the arc gap further increases the electric field diminishes 

 and the spark line \448i is observed to grow narrow very 

 rapidly until, at a pole distance of 1*51 mm., there occurs an 

 abrupt and considerable drop in its intensity. At this point 



the value of the applied electric field is down at 528 ^^. 



. cm - 



After this event the spark line shows only very feebly, dying 



out gradually; the arc flash, however, continues and comes 

 to an end when the tip of the movable electrode has reached 

 a distance of 4' 76 mm. from the stationary one, corresponding 

 to an applied fioldof only 168 — -. In order to see whether 

 there is any connexion between the acting electric field and 

 the emission of spark lines during the second phase, it is 

 necessary to compare the values of the applied fields at the 

 moment of the abrupt cessation of the intense emission of 

 these lines under various electrical and other conditions. 

 For, if the emission of spark lines is really governed by 

 electric forces, it seems plausible to assume that such an 

 important event as the sudden stopping of their radiations 



