356 On the Phosphorescent Glow in Gases. 



lias shown that there is an emanation of gaseous particles 

 from the cathode for a long time after the discharge has 

 passed. It seems probable that the emanation of particles 

 from the cathode for so long a time may be connected with 

 the observation I have described. 



It is difficult to say whether this phenomenon is one of 

 fluorescence of the glass or of a layer of gas on the glass round 

 the cathode. The effect appears to be instantaneous, and to 

 accompany the ring-discharge ; but it occurs only when the 

 pressure in the gas is so low that the phosphorescent glow 

 appears round the cathode c when the discharge is sent 

 between c d. 



Meissner and also De la Rue and Hugo Miiller have shown 

 that when a discharge passes through a gas there is a sudden 

 change of pressure, in some instances amounting to 30 per 

 cent. They have shown that this is not due to heating. 



The experiments of Hertz (Wied. Ann* xix. p. 78, 1883) 

 also show that the discharge is an explosive effect, and that 

 this is more vigorous at the anode than at the cathode. For 

 instance, a tube with a narrow mouth had the cathode close 

 to the open end and the anode at the bottom, and the whole 

 was in the interior of a bell jar. When a discharge was sent 

 between the electrodes from a leyden-jar, a glow was pro- 

 duced which was blown out of the tube to some distance from 

 the open end. 



This would explain the fluorescence round the cathode e 

 (fig. 3), since the explosive effects of the ring-discharge would 

 be to compress the gas round the electrode e. That the phos- 

 phorescence does not last long may be compensated for by the 

 fact that it is extremely brilliant, and the phosphorescence is 

 always a time-integral. 



The explosive effect of the ring-discharge would also account 

 for the curious fact that the after-glow in one of the long tubes 

 at pressures of about yV mm., when the glow is at its best, 

 appeared to start at the end farthest from the bulb as well 

 as in the bulb, the two moving in opposite directions until they 

 met, when it became uniform throughout the tube. This 

 was doubtless again due to compression at the end of the 

 tube. 



[To be continued.] 



