r 342 ] 



XXX. On the Phosphorescent Glow in Gases. By John 

 B. B. Burke, M.A. [Dublin), B.A. (Res.) Cantab., Trinity 



run....- n-..~i.'j„-* 



College, Cambridge* '. 



Section I 



WHEN a leyden-jar is discharged through a coil o£ a 

 few turns of wire wound round a vacuum-bulb, it 

 has been shown by Prof. J. J. Thomson that at pressures less 

 than 1 cm. of mercury a bright ring-discharge is produced in 

 the gas by the rapid oscillatory currents which are thereby 

 set up. 



Between certain limits of pressure, which vary for different 

 gases, a brilliant phosphorescence follows the passage of the 

 ring-discharge, lasting usually for several seconds, and 

 sometimes for one or two minutes. It can be shown that 

 this phosphorescence is not a mere electrostatic effect on the 

 surface of the walls of the tube, but actually a volume effect 

 in the gas. There is generally, however, with the electrode- 

 less discharge, a faint luminosity which precedes the passage 

 of the spark, and extends throughout the greater portion of 

 the tube ; but this is merely a feeble discharge due to electri- 

 fication of the walls of the tube, and can be easily stopped 

 by putting the coil to earth, or by interposing a sheet of 

 blotting-paper moistened with dilute acid between the coil of 

 wire and the tube, thus screening the electrostatic, but not 

 interfering with the electromagnetic, effects of the discharge 

 through the tube. 



Fig. 1. 



O Oi 



The method of producing the electrodeless discharge was 

 one of the two originally adopted by J. J. Thomson. 



The inner coatings of two leyden-jars (see fig. 1) are 

 * Communicated by the late Professor G. F. FitzGerald, F.R.S. 



