the Occurrence of Enhanced Lines in the Arc. 295 



the liquid film. It is during this phase — namely, within the 

 liquid film — that the spark lines are brought out and attain 

 a relative development comparable to 'that observed in 

 condenser discharges. After the destruction of the film a 

 short-lived arc flash is formed between the fixed and the 

 upward moving electrode, resulting in the establishment of 

 the second phase. During this phase both flame and arc 

 lines are well developed, whereas the spark lines show only 

 feebly, and sometimes stop quite abruptly in the middle of 

 the arc flash, as though some sudden change in the structure 

 of the radiating centre had taken place. According to our 

 estimates the first phase during which the spark lines are 

 strongly emitted lasts from about 0*0001 to 0'0005 second ; 

 the second phase may last up to 0*007 second or even longer. 

 The description of the observed phenomena just given 

 applies to various kinds of liquid films, both insulators and 

 conductors. When the liquid is an electrolyte the electrodes 

 need not be metals. Thus the spark line \ 4481 or mag- 

 nesium is brought out in a film of magnesium sulphate 

 solution placed between graphite electrodes. In addition to 

 the spectrum of the metal vapour the hydrogen lines A, 4862 

 and X65G3 are emitted with all these liquids. Their 

 behaviour is very significant — namely, they are considerably 

 broadened at the beginning of the first phase and grow 

 narrower as the distance between the electrodes increases. 



§ 6. Effects of various gases. 



Since our principal object was to ascertain more precisely 

 at which stage of development of the arc phenomenon 

 various types of lines are emitted, it was essential to draw 

 the arc out by rapidly displacing one of the electrodes in the 

 manner described in the preceding paragraph. In order to 

 accomplish this in a small enclosed space filled with the gas 

 under examination the following method was employed (fig. 3) . 

 A cylindrical glass vessel of two inches diameter and five 

 inches height was closed at the bottom with a stopper which 

 carried the fixed electrode. The top of the glass vessel was 

 cov3red with an elastic rubber membrane through which 

 passed the movable pole. The latter could be brought into 

 contact with and withdrawn vertically from the fixed 

 electrode by means of a mechanical device. The gases 

 employed — namely, hydrogen, nitrogen, oxygen, and coal 

 gas — were passed through this vessel in a constant stream 

 at a little more than atmospheric pressure. 



Without entering into details it will suffice here to state 



